Our Polychrome Past

The Maryland State House Dome as the British would have seen it entering the Chesapeake Bay in the War of 1812

How paint analysis can alter our understanding of a building’s history

a new series looks at how the evolution of paint analysis including fluorescence microscopy and protein staining can help us understand far more than what color our historic buildings were painted – while shinning light on a colorful past we often think of in chaste shades of gray .

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In studying an historic building to learn about its original form and the alterations, additions, and repairs that it has undergone, paint analysis can be a powerful tool to unlocking its secrets.

“Cratering” through paint colors on the dome to uncover the stratigraphy and unlock paint colors history

One of the earliest field methods for paint analysis was to sand a crater in the paint polishing to 600 grit with a little oil or mineral spirits. Visual examination of a paint chip can give some information. Use of a loupe at low power allows you to roughly estimate the number of layers and colors. A tiny chip of paint cast in a clear resin and polished as a cross section can be viewed under a regular light microscope for even more detail.

stratigraphy under uv light

With fluorescence microscopy you can not only determine the colors but distinguish each layer even when the same color has been applied multiple times and determine the type of coatings used (emulsion, oil, natural resin, latex etc.). Understanding the types and sequence of finishes can help in dating the coatings. SEM (scanning electron microscopy) and XRF (X-ray fluorescence) can help identify pigments which often will narrow the date range of use.

Failures after restoration a decade earlier

Knowing the composition of paint layers can also aid in diagnosing paint failure due to incompatibility. For the Maryland State House dome, incompatibility of modern latex paint over 17 layers of oil paints had caused much of the oil to fail and rapidly led to rotting of joints. Up close, it was hard to believe the dome had been “restored” only a decade earlier. What would become even harder to understand however, was how the dome continues to be rendered in white and gray.

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Recyclean rinses away layers of incompatible paint

Understanding the composition of the paints already in place allows for the use of selective paint strippers to remove some layers while leaving the rest intact. When incompatible coatings cause layers beneath to separate and cleave, the microscopy can identify this so that a penetrating resin can be applied that will re-adhere them.  For the dome, we used B72 to ensure the edges of original paint were well-adhered wherever adjoining paint had failed back to wood.

We will explore the paint microscopy process in upcoming postings. For now let’s look at one recently completed project: restoration of the State House Dome where we were able to retain the vast majority of the paint history in place. The Maryland State House dates to 1779 and the current dome was completed in 1792 after storm damage to several earlier versions. This is the oldest continuously operating state house in the country and the Old Senate Chamber of the Maryland State House was where George Washington resigned his military commission in 1783 and, the following spring, where the Treaty of Paris was ratified, officially ending the Revolutionary War. At that time, Maryland’s State House was also functioning as the national capital. More on this history is available on Wikipedia.

Balcony level view from the dome showing one of the copper balls that was installed to replace a missing unit

Although restored less than a decade earlier, signs of failure on the dome were quick to show, even as viewed from the ground. As we prepared to restore the dome – which would require expensive scaffold access – we had to first determine the main cause of failure and decide where our efforts would be focused. We did this by taking samples where the dome sat on the flat roof of the State House and at the balcony level which exits from inside the dome 2/3rd of the way up. We concluded the main issue was paint incompatibility.

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The thick layers of latex overburden (top) removed back to thin, stable oil layers (visible and fluorescence)

The paint failure was largely the result of very heavy layers of latex being applied over 17 layers of oil. Latex is a fantastic way to strip earlier paints. This is largely due to water moving through latex paints, causing them to expand and contract. This movement exploits weakened oil layers as it tugs at the surface. The installation of caulking was also trapping water in the wood shingles that had always been able to breathe, causing the shingles themselves to swell. . Our main focus would be to remove the latex and get back into sound layers of oil paint, while re-establishing the original breathability of the dome system.

What we found in the process of looking for the physical evidence was that it also added to our understanding of the archival record. The paint evidence both confirmed contemporaneous annotations and added to our understanding of the involvement of an important artist in the dome’s expression. What was particularly compelling about our look at the paint history was finding that much of the dome had originally been painted a peachy-flesh tone that was over-coated with a golden glaze. It appeared the intended effect had been a golden dome – on the cheap since resources right after the Revolution were limited. In fact, although the original glaze used might not have held up for long, the golden appearance had been maintained – although in a single coat application of paint – two more times before the color scheme changed. Could it really be correct that the demure gray and white everyone was accustomed to was inaccurate?

Clinking will send you to this image on the Maryland Archives website.

As we began considering the meaning of this golden glaze affect, we considered a sketch made by the nation’s first native-born artist of great note: Maryland’s own Charles Willson Peale. His drawing depicted the dome’s details and annotated the color scheme. It turns out his description of the color was “straw.”

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Shop mockup of the “straw” treatment with a peach base and golden glaze contrasted against the deep gray slate band of the dome

Even more interesting was that where the color of one band was not not annotated we would find during the project that they appeared to have been testing out color schemes back and forth and back and forth in rapid succession because the earliest paints showed no sign of dirt deposition or weathering. So was Peale on site while they were making these color decisions?? Peale’s involvement in recording the paint treatments seen on the dome makes the manner in which the “straw” was achieved far more interesting. Most colors of this period were built up out of several hues and the peach tint that was used as a base for the glaze is the shade used for all female elements in art of the era (the solidity of men was expressed in grayish stone hues). .

From peach to gold: How the early golden finish was achieved with a glaze

 

The white-painted dome of today

Now hidden beneath white-painted slate and cedar shingles with just a hint of naked slate remaining, the evidence remains to inform the future. Never should we assume the past was sepia-toned as the earliest photographs of our ancestors have caused us to believe. Rather than think of them as an artist’s flight of fancy, the works of period artists can often help us to understand the interior and exterior palettes of the era. We hope this blend of archival and physical evidence informing our past has been a good introduction into what paint microscopy can tell us about our more colorful past.

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There is a tendency on preservation projects to sample historic finishes and then obliterate them. To hope that having recorded this information will somehow inform the future is pure fantasy. Most organizations can not find a ten-year old report, let alone anything older. And most of the time they would not even think to search those earlier documents.  We must maintain the evidence in place if it is to inform the future – especially as our ability to analyze the remaining information expands with new means of analysis nearly every decade.

 

Rendering by Malcolm Dax

The paint evidence on this project is fascinating for the curious, so it is unfortunate the  polychrome history was not revealed or re-established for public interpretation. In upcoming posts we will show the results that came from projects that allowed full interpretation of the evidence, making seemingly “dumpy” little buildings that contractors might have felt they were “stuck with” into icons that everyone could appreciate. Far from a simple color analysis tool, in the next few posts we will look further at how fluorescence microscopy can confirm or deny our suspicions, while providing great insight into the past. It can provide important information that helps design and guide the treatment process.

View from the harbor. Renderings of the early paint scheme by Malcolm Dax.

Conservation Process: The ‘Drop’

How to effectively preserve buildings while eliminating the uncertainties, risk and change-orders that plague most preservation projects

 

In any profession, success requires knowledge, tools, and techniques used in the right sequence and at the right time. The preservation of an object – whether a musical instrument or a building – shares creative aspects with the process used to design and create the object, but also has its own set of specialized skills that must be adapted to the project at hand. Anyone trying to shoehorn preservation into a construction mold will not even understand what is possible.

Only through an investigative mockup with all parties involved can the potential of the project be unveiled and the team dynamics and ballet of interrelated skills be choreographed to produce the desired goal. There is a process to conservation that sets it apart from new construction. Failure to recognize the need for this process or to put it into practice wastes time and money, but also can destroy rather than save our heritage as the object is cut to fit a design conceived without an adequate understanding of the challenges ahead.

Contractors have said to me that preservation is so expensive and time consuming, and that they could tear down and rebuild the structure from scratch quicker and cheaper than restoring it. I’ve heard this many times. Of course they couldn’t build the same building. They really have no idea how it was put together. That’s usually where the exchange ends: they go back to their linear world of new construction and I back to mine. 

While their statement bothers me, it does have something interesting behind it: we know more about a building that is yet to be constructed than the building standing in front of us. How can that be? A new building is drawn out in detail, plan views, sections through. Every aspect is already designed, it’s cost known when construction starts. The old building we are standing in front of is not what it seems to our senses. We only see surfaces. Surfaces on top of what?

Watching most preservation projects lurch from crisis to standoff while wracking up astronomical change orders justified under the “unknowns” of a preservation project reminds me of using Google Maps with the wrong filter. It would be like getting in your car and keying the directions to your meeting in an hour only to be shown a 17-hour trip. If you were alert, you might recognize you had your route set on walking mode instead of directions by car. Instead, the common wisdom in preservation these days apparently is to continue on a tortured journey and claim the only way to work on historic buildings is to add at least a 30 to 50% allowance to the budget for “risk mitigation,” rather than question whether the charted route is awry.

But there is another way; one that does not use off-the-shelf products and new construction procedures. The right process creates a feedback loop where new information that is discovered while working on the building is able to be woven into the project in real time.

 

This 1880s building in Washington DC is a good example of a structure that continued to deteriorate for 40 years because each attempt to design a repair plan for it using the standard new-construction-based-restoration process exceeded a reasonable budget. Instead, the on-going leaks were addressed on the interior with regular plaster patching and repainting as water continued to drain in from failing gutters and through the masonry at the projecting bands.

Once the client allowed our conservation team to work with contractors in an evolutionary project design process (as a design-build project), we were able to address only those areas that needed repair but give them the best possible treatments. So how did we do it?

Based on our best understanding of the building at that point, we estimated how much we thought the client’s budget could reasonably accomplish. The chosen contractor agreed to scaffold as much of the building as we expected could be completed. The primary focus was areas of potential public life safety risk from bricks that were beginning to fall out of the projecting bands and building corners to the sidewalk. It was also agreed to scaffold the tower that had been badly shaken and showed new damage after the earthquake. We were unsure how much repair of the tower could be completed, but we thought the budget could at least cover emergency stabilization.

The selected contractor agreed to provide hourly rates for their tradesmen based on their best understanding of the work involved, but understanding they would be required to reprice after a month working with the conservators in late winter on a 25′-wide cornice-to-grade representative section of the building. We refer to this investigation and training panel as a “drop.”

flashing added to protect projecting masonry

For this month the contractor provided their supervisor for the project, a masonry foreman, two masons and two masonry helpers, and two roofer/metal mechanics to work with the conservators. The “drop” allowed all parties to fully inspect the conditions as they dismantled sections of the gutter and projecting bands to determine construction details, worked out repair protocols, and then developed the necessary tools and mortars to repair the brickwork.

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custom pointing tools

The masonry challenges on this project were particularly acute because the fattest joints might be 3/16-1/4″ but were generally 1/8″, complicating the issues of grouting to fill deep voids. The “drop” period also allowed us to do mockups of alterations to the existing design for the historic preservation office to review and approve.

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The bricks were masked (yellow coating around areas being pointed) to allow quick cleanup without using acid

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At the end of a month, everyone from the client to the contractor better understood the complexities of the job. At that point the contractor re-bid their labor and materials costs based on agreed-upon field conditions. This included the masons understanding how the work would be laid out for them.

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At 189 miles of pointing on the building, a 100% repoint was never going to be fundable and was not necessary. Deteriorated mortar was focused at the projecting bands with their unprotected skyward-facing joints and at building corners, especially those that had been damaged when downspouts built into the walls to drain the gutters had failed. In order to address only those joints that needed repointing, the conservators took a very hands-on approach to laying out the work for the masons.

As the A/E and conservator of record, our team went through and marked every inch of joint to be repointed and then totaled the joints with the contractor by building grid. When the grid sheets were completed and totals confirmed by all parties, repointing could begin. In this way only the joints that needed repair were addressed. The conservators worked just ahead of the contractor, determining whether damaged bricks and stone would be replaced or repaired by one of several different methods.

 

 

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Proceeding in this manner, the budget was stretched to complete about 1/3 more of the building than originally envisioned, including complete repairs to the tower, as well as stabilization of 80′ and 150′ retaining walls at sidewalk level that were also becoming unstable.

Let’s look at why this building-focused rather than design-focused project worked so well.

In a nutshell, this graphic describes the evolutionary nature of a process focused on the exact needs of a specific building by incorporating feedback loops that allow conditions to be addressed as they are uncovered during part of the project.

 

 

This stands in stark contrast to the design-driven process that uses the process of new construction and standard AIA documents. When approached that way, the entire project is guided by documents drafted in an office in the absence of enough information about on-site realities. Of course as soon as this type of project begins, new conditions are uncovered that cannot be accommodated by the design.

Here’s a way to look at the standard construction process as our historic resources are normally forced through.

 

The result of unknowns being uncovered in a restoration project using the new construction process is one of two results:

1. Either the change-order machine starts and everyone moves to their adversarial corners blaming everyone else for exceeding the budget, and/or
2. Repairs that are not necessary are carried out in some areas while areas that really need repair are neglected because they had not been addressed in the original design, either of which is a waste of money and leads to further damage to the historic artifact.

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Whenever we first suggest using a ‘drop’ process, we hear one of two things.

1. Architects misconstrue the ‘drop’ with the off-site isolated mockups they have contractors do to choose mortar colors and confirm their masons can do neat work. That sort of mockup overlooks the need to determine the needs of the building.
2. People assume that the ‘drop’ is an additional standalone procedure and therefore an extra expense of unknown value that is optional.

The fact is that doing a ‘drop’ completes actual work on the building and it ensures the budget is preserved along with the building.

 

One other drawback to having projects designed in an architectural office without the benefit of having conservators work through a ‘drop’ with the chosen contractor is that many in the construction world still fail to recognize that preserving requires different skills than making new things and the skills of preservation are not in the trades. In-kind replication of what existed is not the same as preservation. Why replace what already exists when the original is fully serviceable? Preservation is about saving our past, not trying to mimic it. We can only preserve the past when conservators with laboratory and hand skills are integrated into both project design and contractor training. That can only occur when a ‘drop’ is incorporated from the start.

Let’s take another more visual look at how the ‘drop’ can benefit a project by uncovering crucial information in the beginning. This project from the art world helped me to refine the process for the architectural world. In the 1990s, Marigene Butler, head of paintings conservation at the Philadelphia Museum of Art oversaw a project to clean the Landsdowne Room. Working with Ian Bristow and Morgan Phillips, one portion of the room was cleaned to work out the procedures. At the same time, this cleaned area allowed them to show funders what would be gained by the cleaning. Of course, when they started, they thought they were just cleaning fireplace soot and cigar smoke off so the room would not appear dingy. What they uncovered instead surprised everyone.

 

So much for our sepia-toned view of the past!

When Marigene was put in charge of the conservation of the Wyck House in Philadelphia a few years later, she encouraged us to take this same approach for repair of a representative section of the building facade. The result was powerful for fundraising purposes at this non-profit.

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But the benefit of the ‘drop’ is not restricted to helping non-profits who are developing a budget for a future project. It is equally beneficial to projects where a limited budget exists because it prioritizes the money to be spent where it will do the most good. In some ways, it is a further revision of value-engineering a project. Here, we eliminate wasted effort, make repairs that best match the needs of that exact building so they provide long-term repairs instead of short-term bandaids, and nothing important is missed.

There is a fuller description of the ‘drop’ process here on the preservationscience website as excerpted from my 1995 chapter in Architectural Conservation of the Wyck House: A Building as Museum Object.

 

 

 

The past wasn’t so long ago: how a WWI-era concrete building surprised us with its connection to the past

We were recently asked by a developer to look at a large open air shed they are turning into retail space below and offices above. Since the project sought to use historic tax credit funding, they had many preservation entities to satisfy.

The developer wanted to sheath the building in glass, but otherwise leave much of the structure exposed. They needed our help interpreting what is unique and important about the structure. Historic buildings are always trying to tell us a story. While concrete structures are now ubiquitous, what makes this one unique?

On our first visit, the interior was inaccessible, but we were drawn to the unique colorations on the mostly weathered paint surfaces. When we returned to look at the building again on a nice cloudy day, we could see the beautiful formwork with the wood grain clearly visible even 20 feet up on the ceilings.

This very unusual structure looked like Greene & Greene construction or a Japanesque post and beam structure, only this time it is constructed of concrete. Built in 1918 when concrete construction was still developing the procedures for large-scale construction, we are able to see how the forms were constructed. As in all architecture that preceded it, we had the evidence of materials, tool marks and joinery to tell us how the building was constructed.

Unlike today when modular formwork systems are bolted together and reused, every piece of this structure was built in place by carpenters.

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The real beauty here was that they used boards that had left the imprint of their grain in the concrete. There are both sash and circular saw marks visible.

  

Early black and white pictures were available to show conditions at the time of construction. We wondered what we might learn from them. In unison with looking back at the building itself, the answer was quite a lot. We know in the 19th century concrete was often poured at a rate of only a foot or two per day. But it is pretty clear from this site and how the forms are built, that they were doing continuous pours of the 16’ tall columns or entire floors all at once.

The pictures of the forms around the columns show a box made of boards with rangers (horizontal braces) to resist blowout from the extreme pressure on the forms (up to 600#/foot). Whereas by the 1930s the formwork would be made of ⅞” boards, these look to have been created of 1-¼” material. The column forms were reused and thus most of them have much less grain visible. Form building at the time was complicated and expensive. Every effort was made to allow wood to be reused, whether attic sheathing, sub-flooring, or diagonal sheathing.

The boards were rough sawn. In the 1910s it was common to plane a single side to establish a consistent board thickness. Occasionally we see where a board was reversed leaving visible planer marks.

It was also common in concrete structures at this time that if the ceilings were going to be exposed, painted or oiled canvas was put on the upper side of the boards so they would have a smooth ceiling once the formwork was removed. Since this was meant to be a utilitarian building, they did not bother with this step.

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The more we look, the more a building reveals how it was constructed.

We began to see two things: an imprint of every board used in the formwork and an early paint history. We had discovered basically three colors on the building and initially thought we would clean the surfaces, stabilize the original paints and then infill paint to match where missing. But we noticed that almost everywhere – to one degree or another – one of the paints seemed to predominate over the others and on some of the columns where we suspected forms had been reused, we noticed the surface was very sanded and that this color was blended around the sand grains. This suggested something other than paint applied after the fact.

It was common in the late 19th and early 20th century to oil boards as a release agent. By the 1930s trades books reference the inadvisability of oiling boards as it leaves a stained and mottled surface.  They comment that in the early days of concrete formwork when boards were oiled that crews often took the forms off too early. But at least the mid-1920s, most trades manuals had concluded that taking forms off early was inadvisable. Instead, since concrete shrinks,  just by waiting the forms would separate on their own when the concrete was cured enough to support itself.

We conducted an experiment by taking some boards with a pronounced grain, oiling them with linseed oil, and put mortar on the boards and let it set for about a week. Sure enough, the surface had a grayish tan coating on it once the mortar was removed. So what appeared to be paint appears to have been another remnant of the original construction process. The bases of the columns close to the perimeter were more yellow and faded out where the sunlight had hit them, but on the ceiling the color was more evenly gray. And on the top side of beams you are simply looking at gray concrete because it had never been in contact with formwork.

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After using a Recyclean to remove dirt and soot, we had  three main colors to consider.  In the end,  the tannish-gray (seen in the cleaned band) was selected for the entire space as it most represented the appearance of the oiled formwork. We opted to paint in matte casein so the wood grain would “read” accurately.

Coming back to interpretation, this is a perfect example of the technology of that time with what was a relatively new method of building. However if we were to interpret the wooden formwork as important to the buildings story, we were presented with the challenge of nearly a hundred years worth of indifferent patches and repairs to the concrete that completely obliterated the board patterns and graining. And the new configuration further complicated the plan by intending to partially enclose some of the upper openings to fit smaller windows using concrete block. Both of these were aesthetic problems to overcome.

   

Our initial thoughts were to use paint to faux bois the concrete so even damaged areas would “read” as grained boards. We also tried making silicone rubber molds so we could stamp graining on, but single dimensional lines would not work given the many angles of daylight hitting the walls throughout the day. We eventually concluded that we while we would use faux bois graining tools, they would be used to tool a cement slurry that we could sand or put aggregate into match that particular location that we were graining.

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The Matching Process

A week was spent grinding down concrete patches to the plane of the surrounding wall using a diamond cup grinder. Then we needed to recreate the joints between boards where missing. Finally we had every kind of grain from flat sawn to quartered with knots and every variation in between to figure out how to recreate mid-board to match what remained on either side. And then we had to figure out the timing of adding to this graining the necessary tool marks (circular saw and vertical sash saw marks, as well as planer marks).

   

It took some time to work out the timing, tooling, sequencing and sandedness of each surface – and I can’t say the results were always completely successful. But now every visitor to the space is once again aware of the wooden formwork in every office as opposed to being confronted by the tremendous numbers of patches that existed when we started.

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The Resulting Appearance and its Place in the Building’s Story

How do you interpret and protect uniqueness? There are several stories here.  Why preserve things? Why are things from the past important? How do you learn to read their story or listen to them? It has to be a multifaceted undertaking: you have to reach out to the building as it offers up its secrets. You have to make an effort.

Concrete is ubiquitous now, but was a new construction material in 1917. Concurrent with this project, we were working on another building constructed in the 1830s by one of Thomas Jefferson’s carpenters where solid timbers make up the post and beam structure. Here, just 80 years later (a single lifetime), is the same post and beam detail but the wood is no longer the structural material. It is now the form for a plastic material (concrete).

   

It took us trying to put what we saw into the context of history or people and building technology, asking why was it there. While reviewing archival sources, we considered what we have learned in the last 50 years of our own work (I remember oiled formwork still existed for certain applications when I first started in the trades). And each time we went back to look at the building, we saw some things a little more clearly and also saw something else we had missed previously.

An important tool in understanding buildings is the taking of minute samples for chemical and microscopic analysis. Too often in preservation, sampling is done just to check off a box. Instead, sampling must be part of a question.

The results of laboratory analysis can add to the story of what these things were, what has happened to them over their life, and to determine the cause of their current distress. We engaged and made friends with this structure so we could establish a meaningful story which would allow the building to be converted for modern use with an important story of its earlier life remaining for appreciation. If you don’t ask the questions beforehand, you usually lose most of the evidence.

The unique timbers of the this building’s construction are gone (and that caliber of timber largely unobtainable today) but they are telegraphed to the present in the concrete.

With the beams now exposed within a modern interior, we have an unexpected result: the hard concrete becomes the softening component and the tan-gray paint, created from reds and greens rather than blacks and whites, undulates in tone depending on daylight, shadow, and various temperatures of modern lighting to create a very pleasing appearance.

  

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For more information about casein paint on masonry, check out this post. 

The Conservators Point of View: How do we assess things that are out of reach?

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Best practices in terms of diagnosing building problems requires that you get up close and see everything, keeping in mind that most visible deterioration is a symptom of underlying causes.

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But accessing problem areas hasn’t always been an easy or inexpensive option. For example, at Christmas time 2003, we were called in for an emergency life safety assessment at the Department of Commerce Building (DOC) in DC. It took a week to organize the effort and thousands of dollars to rent three 120’ lifts that could place us at the right spot 80’ in the air.

Here we are driving down 14th St between Pennsylvania and Constitution Avenues to  determine the cause of large pieces of stone cornice crashing to the sidewalks below. While inspecting the gutter detailing, we found skyward facing joints and popped seams (the gutter had 75’ runs between expansion joints). Needless to say this inspection was extremely expensive and caused significant traffic disruptions.

   

At the Empire State Building constructed just a few years before DOC, our investigations had confirmed the use of ferrous fasteners. Corrosive expansion of these fasteners was jacking the stone apart, allowing rainwater to enter and freeze. By partial dismantling of one damaged section of DOC cornice we confirmed that the fasteners were bronze and stable. Water leaking into the cornice from the bad gutter design had finally undermined the structural integrity of seven stones that had vertical bedding planes.

Another way to inspect from above is to rappel down. This requires a lot of planning and safety harnesses. However, the risk of damage to the roof from this sort of work needs to be carefully weighed.

The value of high-end optics like a Leica spotting scope should not be ignored.  In fact from a 1/3 of a mile away we can see the joints and cracks of post-earthquake damage on the Washington Monument, as well as the see the construction crew building the scaffolding for repairs.

Click on any image for a larger view

Early inspections are important for prioritizing funds for projects by reducing the number unknowns going in and the more you know ahead of time, the fewer change orders later. If you want to see more about the benefits of taking the visual inspection through to an in-place mockup to reveal all of the conditions and streamline the process of repair to significantly reduce costs, take a look at this project summary.

Even more for smaller but important buildings without the benefit of large funding sources, it is important for us to find practical ways to get to the necessary information to diagnose problems. For example, how can we help the retired homeowner trying to care for their historic house on limited funds? Do we tell them that to inspect their chimney will require lifts (if accessible to the site) or $6,000 in scaffolding just to access the chimney, not knowing whether based on what we find they will even be able to afford the full repair while the scaffolding is up? Or do we find better alternatives to get at this information?

With all of the distressing news about drones from surveillance to delivery of packages both deadly and from Amazon, we’ve been thinking a lot about this technology. Despite reservations, it might be the ideal solution to determine roof condition, gutter function, whether chimneys are capped and the state of roof-to-chimney intersection flashing … as these are crucial in designing a project.

     

     click here to view a short video in action.

It was important for us to see how the roof on this 1753 house was fairing after several brutal storms and some earthquake damage. In fact within minutes we found missing ridge shingles and some loose flashing.

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Our first visit to a remote ruin:

We are in the early days of our experience with using a simple helo and high-quality video, but you can see here how effortlessly we were able to assess both the existing conditions of this house ruins and its surroundings.

click for video

We quickly learned that although the capitals are filled with concrete, it is cracked and taking on water which is deteriorating the cast iron further. (We also found these cement additions to be nicely signed and dated.) We were also able to discover original lime fluting hidden beneath the later cement wash. The brick columns cores, wherever exposed, proved to be in excellent shape.

Going forward, we can see many additional uses of this aerial platform. By the way it is controlled from the ground using GPS location and barometric sensors to stabilize the recordation and we are able to switch from high-frame rate video to high-definition stills in flight while viewing the progress from our iPad or iPhone.

Not unlike the lunar module collecting information on the moon, before long I’m sure we will have helos carrying instrument arrays for organic and inorganic sampling. For now I’m aiming to start having my little helo deposit gel sampling disks that indicate types of biological material and chemical components of staining.

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Carbon fiber masonry restraint goes big

Soon after the Menokin chimney, we had a project to repair an 1870s brick building. This era of construction meant ⅛” black mortar joints that had suffered deferred maintenance for at least the last 70 years. Nearly all mortar from the decorative projecting bands of masonry was gone where water had worked down through the skyward-facing joints. Failing internal drain leaders at the building corners had also caused major deterioration of mortar through the depth of the walls. Some of this drain failure appeared to be related to bad design that put dissimilar metals in contact with the anodic cast iron drains downstream of large copper (cathodic) gutters.

The dark decorative terra cotta band typifies skyward facing joints

Had the repointing project occurred two years earlier, it is likely the damage the building and tower suffered from the 2011 earthquake would not have been so severe. At the tower in particular, the shaking loosened bricks at the round windows and there was corner cracking as well. Some of this was no doubt increased by the shifting cantilevered balconies above. But these windows also span between the cast iron stair landings inside which meant they were moving freely between two hard points inside that were pushing on the building above and below during the earthquake. The metal band holding the polycarbonate window also created a hard point.

Rather than do a typical repair with a series of criss-crossing through-tower ties with ugly pattress plates on the exterior, we decided that carbon fiber buried in the joints would make a more elegant restraint to future outward thrust around these windows. We opted to wrap the tower in epoxy-impregnated folded CF tape plus filled the center of this “C” with epoxy to create a custom built-in-place rigid beam.

In addition to drawings, we did a simple mockup in the shop to 1) help us work out any bugs and 2) to help describe the process to the contractor so they could bid this uncommon repair. We were lucky that on the tower the joints were closer to 1/4″ high.

Brushing epoxy into CF weave

Screeding excess epoxy off surface

Opening the folded CF into a “C”

Injecting epoxy into the CF fold to form a “beam”

Peeling back the masking to reveal clean brick

The bricks were masked at each joint to be pointed on this project. Remnants of 1960s brick waterproofing turned white in contact with high pH materials, so we had to isolate the brick faces when repointing. Because this step eliminated staining of the brick faces, there was essentially no masonry cleaning required, except local brushing with a vinegar/water solution in a few spots.

Obviously when repointing with lime mortar which is slower to set than portland mortars, it is not an option to hose the entire building down with muriatic acid after the fact because the masonry work was done sloppily. This crew was pretty neat, but with the masking, they could actually afford to be messier with their pointing because the masking would remove any debris and stains. We were very appreciative to have this “Rubber Mask” from American Building Restoration to protect the waterproofed bricks from turning white, but it also took away the cleaning step which is such an integral (and pricey) part of most masonry project budgets. This means we also eliminated the efflorescence risk that comes from leftover acids and the risk of biological growth that plagues so many projects after cleaning due to residual surfactants that become food sources.

You’ll notice that because repairs on this building were handled on an as-needed basis inch by inch, the conservation team determined the areas needing repair and chalked them for the masons. In order to agree on what all these smaller repairs added up to, the conservator transferred the marks to the drawings and totaled the lineal inches in concert with the masonry crew so the amount of billable work was agreed upon in advance of repointing. You’ll note the CF annotation for the carbon fiber course. Although this meant more time for the conservators, it stretched the budget for repairs. In fact when this project started there was no expectation of being able to complete repairs to the tower or the “moats,” but because we only repaired joints that needed it, these projects were able to be completed for the same budget that originally was only intended for repairing the main building out at the public corner where falling bricks had become a life safety hazard.

In spite of the unique nature of the tower’s carbon fiber stabilization, we had a very agreeable masonry team from Atlantic Refinishing & Restoration that worked with us on this one-off installation. The tape was installed two courses above and two courses below the round windows, wrapping the exterior and then the ends overlapped for a foot before being turned up and locked around a brick above and below into the adjoining courses.

It took several guys to keep the tape uncoiling evenly into a C and not have it snag on the bricks. They quickly learned how to inject the bedding epoxy, press and fold the CF open into a “C” and keep it open with wood wedges. Then when it came time to inject the epoxy that would fill the “C” to make it rigid, this was a quick and seamless process. We inserted this carbon fiber tension “beam” recessed from the brick faces by 2” so that the front of the joint could be properly pointed afterwards. Superintendent JD Stinner (black shirt) and Masons Mike Manning (white suit) and Mike Barnett were the crew.

Wrapping the corners was the biggest challenge we faced.

In order to impregnate the tape as it went into the joint without wearing the epoxy, a board was hung over the scaffold rail and up to the wall that allowed the tape to be draped across it where epoxy was brushed on and the excess wiped off with a screed right before placing the CF in the joint.

When the entire perimeter CF was installed into its C formation at the appropriate depth, the crew came through with tubes of the epoxy to fill the center of the carbon fiber. This was then left to set overnight before the rest of the joint was pointed the next morning.

One of the other last-minute additions to the first phase of this project that became possible due to stretching the budget was repairs to two of the retaining walls that held back the earth around the basement light wells which were bowing. (These retaining walls were humorously referred to as “moats.”) These 10′ tall retaining walls were unbuttressed and stretched between 80’ and 150’ in length without internal restraint to counteract the thrust of the earth. Bracing inside the light well would have been unattractive and would have potentially hampered the movement of equipment in and out of the building. Likewise, digging out the earth behind them and installing proper buttressing was not an option since they were either under public sidewalks and entangled in electrical substations below the street or under the elaborate (and in daily use) childcare playground for the building’s occupants. We needed to find a way to resist the thrust of these light well walls from inside the “moat” that was relatively unobtrusive.

At the sidewalk moat where only the top few feet had bowed above where some earlier bracing had been installed, we opted to relay the top several courses of the wall and reset the stone cap, laying carbon fiber into the top few courses as it was relaid and ensuring the ends of the CF “beams” were pinned into the return walls.

In the 150’ long moat against the childcare area, we integrated a single continuous course of carbon fiber. This was aligned to bear against the back of star plates set over threaded rod that tied the wall back to concrete deadmen strategically located in the playground so that the holes could be dug, poured, and the padding relaid over a holiday weekend.

 

Carbon Fiber: From Woodwork to Masonry

This is part of larger series on carbon fiber (CF). If you are just joining this blog now, please take a moment to review the previous CF posts.  

For our regular readers, we will soon be switching topics to early 20^th century concrete formwork repair for a real change of pace that mixes 19^th century construction techniques and the imprint of the original timbers in early concrete construction to discuss how damaged areas can be repaired unobtrusively.

Examples of the available array of CF and kevlar

In our initial attempts to determine which CF cloths and resins to use, we reviewed a lot of technical literature. Too often though it was focused only on the how-to of layup for specific uses in industries such as boats or airplanes. Nowhere was it articulated why one type of weave or directional cloth was used in each part or function so that we could determine the best materials for the types of stresses we would be placing on our artifact supports.

As a designer, I needed the fundamental information on how the woven textile system works so that I could apply it to the particular problems we faced on this project. The best information – that which broke the logjam for us – was not listed as a technical book. Rather it was a coffee table book resulting from an exhibit at the Cooper Hewitt a few years earlier and that was edited and largely written by textiles department exhibitions curator Matilda McQuaid. I can’t recommend the book enough to anyone interested in learning to work with carbon fiber in non-standard ways.

Extreme Textiles: Designing for High Performance concisely explained why each material, weave, and directional choice is chosen for hundreds of uses across dozens of industries from machine parts to surgical implants, from lunar landing pods to buildings of woven structural elements.

“As composite reinforcements, textiles offer a high level of customization with regard to type and weight of fiber, use of combinations of fibers, and the use of different weaves to maximize the density of fibers in a given direction. Fiber strength is greatest along the length. The strength of composite materials derives from the intentional use of this directional nature. While glass fibers are the most commonly used for composites, for high-performance products the fiber used is often carbon or aramid, or a combination of their two, because of their superior strength and light weight.

One advantage of composite construction is the ability to make a complex form in one piece, called monocoque construction. A woven textile is hand-laid in a mold; the piece is wetted out with resin and cured in an autoclave. The textile can also be impregnanted with resin and cured without a wet stage. The same drape of hand that makes twill the preferred weave for most apparel is also desirable for creating the complex forms of boats, paddles, bicycle frames, and other sports equipment. The weft in a twill, rather than crossing under and over each consecutive warp, floats over more than one warp, creating the marked diagonal effect typical of twills.”

From the chapter Stronger in “Extreme Textiles” by Matilda McQuaid

For an architectural conservator, I also appreciated how this book put the use of textiles in the historical context of man’s earliest permanent dwellings with wattle and daub and then went on to cover the last hundred years from the early 20^th century attempts to design multilevel interwoven cities by the likes of Buckminster Fuller and right up through modern construction using lightweight, flexible armatures to support glass and and other cladding far heavier than the frame.

“While many [modern curtain wall structures] depend on highly advanced materials and technology, the principles have ancient roots using humble fabrics. Recent archaeological finds date the beginnings of permanent construction almost immediately after the last ice age, approximately seven thousand years ago, contemporary with tearless evidence of woven textiles. As the nomadic existence of the Paleolithic age gave way to the first settlements, and transportable tent like huts clad in animal skins were replaced by architecture designed to last for generations, the first building materials to emerge were not masonry, but woven. A meshwork of small, flexible branches formed the under layer of cladding and served to brace the larger structural members, stiffening the then-circular house….

Most traditional buildings engineered today use components of construction fabricated in a strict order…The order of construction is roughly parallel to a steady decrease in size of each element, and in the hierarchy of support. Each must carry the combined load of every subsequent element that is later added to it. The first stages of construction therefore form the immovable, stable base that supports everything that is to come. 

In a textile, the process is quite different. Every fiber has an integral role in maintaining structure, each as important as its neighbor. The fibers are long, usually spanning the entire length and width of the textile. The structural properties are evenly distributed throughout the fabric, as each thread connects to the others. Instead of fixed, rigid connections based on compression, textile structures use tension. The binding of one fiber to the next is achieved through the tension exerted by the immediately adjacent fibers. Rather than relying on support from the previous, stronger member, the system is circular, holding itself in balance…

[V]isionary Buckminster Fuller developed the concept of synergy, meaning the “behavior of whole systems unpredicated by the behavior of their parts taken separately.” During a career of pioneering work in engineering space-frame and tensegrity systems, Fuller explored complex interactions of structural elements that reinforce the whole. Using synergy, he described textiles as exemplary systems for architecture. A distribution of forces occurs as each thread joins a larger number of similar threads. The whole collection can tolerate extensive damage, spreading the risk throughout many elements. If one thread snaps, the proximity of identical components, and their flexibility, allows the system to adapt dynamically to the new condition.”  

– A Transformed Architecture chapter in “Extreme Textiles,” written by Philip Beesley and Sean Hanna

As stated in the introduction to carbon fiber I wrote for the Menokin project engineers, my decision to look into the use of reversible carbon fiber armatures had come from discussions with Chemist Richard Wolbers regarding my concerns about the lifespan of components such as epoxy resins normally used to impregnate the artifact and act as a consolidant.  We have long justified the use of epoxy consolidants when we would lose the artifact and all of its information if we did not use modern resins. But it seems to me that it is now time to move away from irreversible impregnation of artifacts wherever possible, especially given that the resins we have been using often have a shorter lifespan than the artifacts that we are purporting to save.

Following on this rationale, we realized that if the carbon fiber could act as a reversible support, then if the adhesive failed, the support could be removed without affecting the object. Our stress testing to failure had shown the weak spot was within the wood itself. The failure was never within the carbon fiber or in its  bond to the wood. In other words, the epoxies and the carbon fiber are far stronger than the wood. But the further we revised our designs, the more we realized that in many cases the CF prosthesis does not necessarily need to be bonded to the artifact. It just needs to be held in place. When bonding to the artifact was necessary, it could be adhered with an easily-reversible thermoplastic resin that a hair dryer could release.

In addition to the structural supports designed for the woodwork at Menokin, we also realized there might be uses for the infinite variety of weaves, ropes, composite fibers using Kevlar and aramids, etc. in the stabilization of the masonry as well. Our first use of carbon fiber on the building came on one of the main four-flue chimneys.

This chimney had a vertical crack running from the top down to just above the second floor mantle height. We knew gravity would pull more debris into the crack as the masonry swelled and shrank through seasonal movement. The debris from shattered mortar in a crack works its way down, essentially further jacking the crack open and restricting it from closing back up.

Aside from a few lost bricks, a sound chimney cap

Four sound flues with dividers to the top

The colony of pigeons vying for position on top of the chimneys wasn’t helping the situation, but in spite of the alarming appearance of the top of the chimney on two sides, all of the flue dividers were intact. Aside from the crack and the top few courses of brickwork that had received the most severe weathering, the original mortar in the chimney was quite sound in spite of 230 years of non-existent maintenance.

Straps around the chimney for interim support. Adding angle iron to the corners between straps further improves restraint.

We had banded the top of the chimney while excavation and stabilization had continued below. Now, after addressing the problems that had caused the original crack to start, we decided the best approach was to leave the chimney crack where it was, but to repoint along the line of the failed mortar at the crack.

Wedges of rolled lead were used to secure the carbon fiber in the joint until it could be pointed.

While the chimney masonry was not particularly out of alignment or beyond its tipping point, we decided to provide a bit of additional restraint by laying carbon fiber into several joints around the exterior. This included “stitching” every few courses across the crack as well as wrapping the full perimeter of the chimney at three locations.

One thing that is hard to see in these photographs is how we secured the ends during a full perimeter wrap of the chimney. The carbon fiber coming around at the end was lapped over itself in the joint about a foot before one end was turned up and the other was turned down and then wrapped back the alternate direction around bricks into the course above and below, essentially creating a lock.

A spool of CF rests on the re-mortared chimney top

Because the building is being interpreted as a ruin, we opted not to infill missing brick, but did mortar around loose brick at the top. Unsure what the working characteristics of the somewhat “sticky” carbon fibers would be against rough masonry, we tested both a 2” wide woven tape and a 3k-strand “rope” known as tow. The spooled tow was significantly easier to lay into the joint, but it did also tend to catch on the rough edges of the irregular masonry.

As we pointed over the CF, the chimney began to take on a new appearance. (Wet mortar appears brownish).

With the 2” tape, we folded it in half in the joint, using the lead wedges to hold it open in a C that we could pack with mortar. This was difficult to lay into place with a single person in the bucket lift, but may have created a more durable fit than the tow. Of course the goal here was not to “freeze” the chimney since it would still want to move seasonally. Rather we wanted a minimal restraint against any additional tendency to move outward.

Pigeon heaven video from the top of the chimney

To finish, the “C” fold of tape was pointed (Video)

For those who are interested, these videos show the conditions and work in progress.

The Virginia earthquake that followed our chimney repair two years later confirmed that this methodology was sound. With chimney failures throughout the region after that  shaking, many engineers ordered that chimneys and walls with limited damage be dismantled and rebuilt. But our stabilized Menokin chimney survived intact.

We were looking at lots of buildings in the region after the earthquake and an aside to this story is that most of the damage that occurred with historic masonry was directly related to where modern hard materials had been inserted as infill into flexible historic masonry. Remember that the main function of lime mortar is to cushion masonry units thereby distributing loads evenly. For example, where chimneys above the roofline were rebuilt in portland they hopped off onto the roof, at the National Building Museum, the historic masonry around every altered doorway cracked from the hard infill while the rest of this nearly city block square building was otherwise unscathed, and the project we were preparing to start nearby (the object of our next blog post) saw damage occur around the tower’s circular windows due in large part to extreme deferred maintenance.

Before we continue on to discuss our plans for creating through-wall bonding stabilization of the rubble walls at Menokin, in our next post we will deviate to another project where we used the folded carbon fiber tape in masonry joints on a larger scale than was required for the Menokin chimney.

We referred in this post to the masonry not being past its tipping point and therefore eligible for stabilization in place rather than realignment or relaying. For those who are interested in better understanding when masonry should be deemed unstable, check out this informative blog post.

Carbon Fiber Repair Options for Historic Buildings, Woodwork – Part 2

We were looking at every fragment of Menokin from the standpoint of being able to return it to the building. Over the last 40 years we had developed many consolidation and repair techniques, but as stated earlier, this was an opportunity to improve the art; to go where we hadn’t gone before; to go for more elegant and reversible solutions.

We were calculating the loads and stresses of the various intersections in the building and making prostheses to test what their size and dimensions would need to be to support these loads. In some places we could do invisible mending, but in many cases where there has been no solution before, we began to wonder whether a visible piece of carbon fiber tape support would be a reasonable response. It is honest and it highlights the original as is without compromising its integrity but while augmenting/supporting so that it can return to its place in the building. This way we would not have done anything to re-write history.

Menokin is a worst case, almost nightmarish situation, but in repairing it,  much like surgeons in a war zone, it functions as a laboratory to solve problems that could have applications in other arenas, adding to our skill and our toolbox of solutions. It certainly might make sense in many buildings to, for example,  support the basement side of a sagging floor joist rather than cut it and sister or put up lolly columns to carry the floors or completely replace the joist, cutting the walls to fit in the new. Now we might have more discreet repair options for many building challenges.

Continuing in my explanations to Tim Macfarlane in December of 2007, I wrote:

“Following on our earlier discussions with you about the paucity of statistics regarding strength of old timbers versus modern construction lumber and how to determine the remaining strength of weakened original timbers and joint intersections, we carried out some simple experiments to measure the force required to bend an unsupported dimensional piece of wood and then that same piece with one layer of CF bonded to a side.

The latter showed a large increase in stiffness.

These are 2″ x 2″ yellow pine segments adhered on one edge only of a strip of CF tape. You can see how flexible it is.

Yet when aligned horizontally so the blocks touch, it supports itself without deflection.

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Click here to see how it responds to pressure.

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Continuing my explanation to Tim: “If a piece of CF tape could strengthen a 2×2, why not a rafter? I calculated the loads on the joist ends for the second floor of the NE quadrant to see what we really need.

Working through typical timber intersections in the structural joinery of the Menokin framing, I focused on several problems: need to stiffen a weakened timber that might have missing areas where it crossed other timbers and fit into a mortise; weakened, eroded, or partially missing tenoned ends and mortises; and timbers with their cores eaten away by termites leaving strong exterior shells and often with large mortises and original tooling intact.”

Pounds per square inch was not great (I estimated around 100), but I realized each joist end was actually bearing on only 12 square inches of contact surface in the mortise so this put a lot of weight on the lower edge of a relatively short cross-section of the girder. What if we could increase the square inches supporting that weight, thus lessening the possibility of shear failure? This lead to the CF mortise insert (see drawing), with the idea being that the CF insert conforms to the faceted end of the tenon and pockets into the mortise in a strong bedding medium, maybe a silicone rubber or urethane. In this way the weight would be transferred to a larger area.

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Here I was trying to demonstrate the ease of recreating the volume of missing elements, but I was also working how would you create these repairs if you were scaling them (which always has to be part of the planning).

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In my mind while working out these techniques on the bench is how you would scale them up. It is one thing to cast in an 8” section of beam; another to do it in a beam 13’ long. Here I used saran wrap as the mold release. So it was just a little thing, but gave me important information towards scaling up to bigger timbers.

      

Remember those mittens you had as a kid that were attached with the string that ran through your coat so you couldn’t loose them? We’ve begun to imagine a joist with each end resting in a CF mortise with CF tape connecting the two ends adhered along the bottom of the joist or folded and set in a narrow groove.

Another structural solution that needed to be developed:

Where we have discontinuous elements, could we complete that missing section of timber to meet the glass envelope planned for Menokin?

 

In the shop I took an old pine timber and cut it on the bandsaw to replicate a typical eroded joist end. The idea was to make a casting of the end like your dentist does in capping your tooth. By creating an acrylic, glass or laminated composite that fit to the timber and had a structural tenon on the other end, we could bridge the gap.

   

Here’s how this would look in the house

      

Click on any image to enlarge

For those interested in seeing promotional videos and books developed by the conservation team with assistance from Malcolm Dax to explain their Menokin Glass House concept and specifically the methods to reintroduce damaged timbers back into the building can find that information here.

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We had mainly been dealing with timber elements, but now we started to think about how these techniques could be used to strengthen the masonry of the building…coming up in the next post.