Carbon Fiber Repair for Historic Buildings, Intro

The following is our 2007 introduction to timber and masonry strengthening approaches we were investigating for the Menokin ruin in Warsaw, VA, based on a retrospective of techniques available at that time but with an eye toward expanding the toolkit.

At the time we were just completing the first phases of extraction and cataloguing of fallen elements from the basements. We had just completed emergency stabilization to keep the one remaining relatively sound quadrant from buckling out into the field, so it was now even clearer how important it was to enclose the building to protect it from the elements. (An earlier shed roof had worsened conditions for the building, making clear the need to enclose the building at the existing walls.)

Menokin start in 2006: Emergency stabilization to keep the NE Quadrant from collapse when the cornerstone collapsed in freezing weather.

We had just made our pitch to renowned glass engineer Tim Macfarlane to join the team. He was immediately interested in working with us to design a means of enclosing the missing walls with glass.

But rather than just enclose the building with glass, we intended to return the original salvaged timbers to their former locations with glass providing an armature for reinstalling the original panelling, mantles, trim, and doors that had been put in storage decades earlier. Why view the building elements in a separate facility when we could put them back in the house? By reinstalling all the salvaged materials back in the house integrated with glass we could also provide an unusual educational context where visitors could see how everything went together by being able to see the backsides of trim and the actual structure of the timber framing sandwiched between glass floors.

Menokin Glass House as envisioned by the team of Charles A. Phillips, AIA; Engineer Tim Macfarlane, and John Greenwalt Lee, PA-AIC.

Tim Macfarlane had been involved in engineering solutions for significant Georgian architecture in the UK earlier in his career (and in the coming years would prove to have more practical and low-tech/cost-effective solutions for historic building stabilization than any engineer we have worked with in decades), he had become renowned for the most avant garde glass structures such as the Apple Store “Cube” in Manhattan and cantilevered glass Metro entrances throughout Japan. In order to bring him up to date with the current state of timber conservation if we were to reintroduce damaged timbers to a composite timber and glass structure.

After extraction of the fallen debris pushing the Menokin Ruin walls apart and adding excess load to weakened floors, the bowing and cracked walls were realigned and then grouted for stabilization

We had been working to stabilize the Northeast quadrant, mostly using temporary measures of wedges, grout, and temporary windows to keep the weather out, along with supports under beams and sagging plaster and lath. The second phase of repair that was about to begin would include structural repair to individual elements; plus realignment and reconnecting these elements to reestablish structural integrity of the girders, joists, studs and rafters.

Charles Phillips, AIA and John Greenwalt Lee, PA-AIC had been developing and trying to improve techniques from one project to the next over decades across a variety of materials, including less-invasive repairs to structural timbers. We needed to give Tim a retrospective and reflection on the evolution of these processes over the last thirty years.

The beginning of the modern “Preservation Movement” started from a pretty basic understanding of what would be involved in moving from a replace-in-kind restoration approach to one of trying to save original materials as valuable artifacts in their own right. The approach then (and too often today as well) was to tear the entire element out even though the damaged portion may have represented a small percentage of the whole and replace it with “in-kind” materials. “In-kind” is just a good sounding phase that lets architects off the hook with the Secretary of the Interior’s Standards and leaves the contractor to effectively make preservation decisions. But the result is always the same: more loss of the original artifact due to laziness and a general lack of respect/excitement when touching the real artifact.

For information on how to approach historic buildings in a manner that can preserve historic elements while saving money, time and frustration through a more appropriate project design and contracting process, see this post.

Repairs should augment the original functionality without replacing anything.

Much of this is basic: for instance increasing strength by using bolts, washers and nuts through an intersection; or nailing vertical pieces against a stud to increase the support to a joist or plate above; or sistering additional joists to existing ones to increase the stiffness to bending of the floor above; or metal plates nailed or riveted across joints to support elements like the intersections of roofing elements or a bridge truss. 

Next there are the less common dutchmen-type repairs to infill missing areas or extend a damaged part that connects to other elements like joist tenons that rest on a sill mortise. Repairs are supposed to be designed rationally (if not scientifically or mathematically) to determine the strength by looking at the structural needs and understanding how the full structural system works.

In my experience, this sort of practical approach to augmenting rather than replacing original elements and systems rarely happens … and less so with each passing year as preservation and restoration becoming interchangeable ideas.

Thirty years ago, preservation of structures using modern materials and techniques was the norm because that was all that was available. Now in preservation we have a great body of technical data about the pathology of deterioration processes and advanced methods for scientific analysis of conditions. Yet people tend to ignore analysis, while making lots of rash assumptions and throwing additional structural supports at perceived problems (surface conditions) without addressing the underlying faults. The consideration that most seems to drive projects is that the structural systems look substantial and finished surfaces pristine in a sort of Disney/Hollywood slickness that is the opposite of authenticity.

To many “saving” historic structures means they have to show that they have been worked on, rather than be allowed — like we would antique furniture — to be appreciated as well-maintained originals.

From 1973, I have continuously worked to make repairs as unobtrusive as possible. This invisible mending approach came from a prior six years of apprenticeship — later in boatbuilding and cabinetmaking, but first in antique musical instrument and furniture restoration. In those trades, the effort was always to try to fully understand the structural needs, the way pieces worked, to find compatible repair materials of the same origin and to design the least intrusive repair method, all with the goal of accomplishing a skillful and invisible repair. As I began to repair buildings instead of furniture and was asked by the owners to “save all original material,” I took it as an interesting challenge and applied myself to using the same ethic on these larger-scale artifacts. Often I was dealing with exposed decorative woodwork that had been weakened by fungal attack and weathering or painter’s scrapers, but were otherwise largely intact.

Epoxy resins that I had used in boatbuilding seemed perfect for the problems of buildings. And in fact much original woodwork would have been lost on famous historic buildings up and down the US East Coast had I not used epoxies. Often the tooled surfaces created by the artisan several hundred years before was intact, yet only held together by many coats of hardened lead paint. If the paint were removed without strengthening the wood, all of the detail would be lost.

Cynthia Taylor is reassembling portions of the Hammond Harwood House front door woodwork in 1975 after the wood was consolidated with epoxy before paint removal to retain original carving.
1975, Cynthia Taylor is reassembling portions of the Hammond Harwood House front door woodwork. This assembly requires referencing a before photograph. The fragile woodwork was first epoxy-consolidated through the paint in place so that the original carving that would otherwise turn to dust could be saved.

Instead, epoxy resins soaked into the soft cellulose fibers provided strength and integrity. With the resins cured, I could remove the paint and repair the missing portions as I would on any woodwork. An advantage of using heat to soften the paint was that it fully cured the epoxy resin to its glass-transition phase. I really enjoyed the challenge of fitting infill pieces of wood that I had shaped to the now-strengthened remaining original sections and then carving them to replicate the patterns. As I learned to sharpen and use each gouge, I began to see how each carving was different, to read the hand of each artisan, and in this the real secret was to catch and imitate the subtle tooling that gives life to decoration.

In this new field of preservation we were striving for a light touch. “Less is more” as one of my early clients used to say. This approach was originally envisioned to exemplify three tenets of conservation – predictability, compatibility, and reversibility – the North Star of this new field was to recognize buildings as important artifacts that should be treated as thoughtfully as objects in museums.

We should not be the last people to experience these buildings in their original configuration and materials. (We can never know what information or diagnostic tool will later allow us greater access to historic information if the evidence has been obliterated.) To be good stewards, we should always strive to change as little as possible — to preserve and not replace — recognizing that every time we work on a building we lose a little more of the original.

As it turns out, the goals of predictability, compatibility and reversibility are difficult to reach and still a long way off. Looking back, I think these goals have been abandoned by most practitioners because the academization of preservation education has given them scant knowledge of materials and processes and no useful hand skills whatsoever.

This leaves preservation architects and restoration contractors to rely on off-the-shelf products and cure-alls supplied by a burgeoning, cynical and unscientific “restoration products industry” … the 21st century’s version of 19th century snake oil sales.

Although epoxy didn’t meet any of the three requirements for conservation treatment, I felt that using it was better than replacement. I hoped in 50 or 100 years it might be possible to remove the epoxy if necessary. And I figured a worst case scenario was someone then would need to preserve the treated piece again or finally replace it, but that at least the information would still exist to inform in the future. I learned to scale up consolidation processes for larger structural timbers and developed methods that combined consolidation of weakened portions with grafted-on pieces and rabbeted, slotted, or dadoed joints with flitch plates.

One of the biggest drawbacks to using 100% solids epoxy resins is the darkening of the treated surface and, unless you are careful, a plastic look. A lot of effort over the years has gone into developing methods to lessen these effects.  A good example was alterations to the epoxy resin processes developed in Poland by Domoslowski for consolidating stone that used heated sand to keep the epoxy away from the surface. Morgan Phillips and I learned to start the cure reaction prior to dilution and then add up to 5 parts ethanol or IPA creating a solvent-cut resin that would easily penetrate a timber and cure in a dispersed form that was somewhat porous to water, strengthened the wood fibers, and yellowed in UV exposure only slightly and then very slowly.

Domoslawski epoxy treatment method adapted for timbers by Conservators John Greenwalt Lee and Morgan Phillips to strengthen wood without changing the appearance.
Domoslawski method adapted to epoxy-strengthen wood without changing the surface appearance.

The floor joists at Londontowne are a good example of this hybrid approach. Using epoxy and the modified Domoslowski method the exterior shell of the joist was toughened without any change in appearance. Then a new core of ¼” stainless steel added to carry the load to a ledger placed in the brick wall. A wood spline filled the slot for the steel, hiding the metal from view, and wooden pegs filled bolt holes. All of this was accomplished from the basement without removal of the joist or damage to the floor above. At completion the augmentation was completely invisible to the visiting public.

This approach for Londontowne was rooted in appreciation and understanding of the original structures (not replacement or “improvement” with modern structural systems) and uses a combination of skilled woodworking, ironmongery and polymer chemistry. I’ve been at it long enough that I have quite a stable of repairs I can return to for evaluating their effectiveness. In most cases my repairs of the last 40 years are still sound, although I try to improve these techniques on each job, aiming for the least intrusive approach. 

Epoxy-to-wood in-place repairs work, but I think they are often still too intrusive and intractable. But by 2007 at Menokin it was time to take things a step further.

I had been visiting the Menokin since the Menokin Foundation first gained control of the ruin. During that twelve years since the 1995 Preservation Magazine article deemed Menokin a “Rubble with a Cause,” I had watched the continuing collapse and dismantlement of the structure until little remained to celebrate. Finally the Board realized they needed to do something different or their only option would be a pile of debris on the ground with a once-there-was-a-building-here historical marker or a very fake but beautified reproduction of the building.

1995 Preservation Magazine feature when much more of the building remained standing

We proposed the original building could be repaired with original timbers set back in place to create the visible 18th century building. What a great opportunity to fill a huge gap in preservation, engineering and architectural education! Here people could experience the process involved in the assessment of structural problems, design of repair solutions, and incremental work on the pieces by craftsmen, architects, engineers and conservators. The idea brings to mind the old artisan saying “We work on the pieces and they work on us.”

With this audacious goal in mind, we began reevaluating existing techniques and trying to imagine better ones for Menokin. One approach could be to conduct sophisticated furniture-type repairs subtly distressed so the repairs were not obvious (see first few sketches of hybrid wood-carbon fiber repairs). These are a challenge and great fun to carry out as they force you to really stretch your craft skills. Another side says lets make the repairs in a modern material – say glass with it’s wow factor – to make an almost invisible non-repair repair. Or maybe we could infill or support pieces on aerogel blocks. These explorations and discussions continued for several years and brought us back to many of the same treatment dilemmas that we have been bumping into on other projects.

Once we accepted the glass house as the only way to protect the Menokin Ruin and realized it had a good chance of succeeding, we decided it was time to move to the next level of conservation techniques. There was no point in picking easy tasks such as trying to make minute improvements in current techniques. Menokin demands we do radical things; take big strides forward. If we could develop a proven methodology to elegantly reload the joists, then we had the methods for saving the rest of the building. By starting with some of the most difficult problems (nearly all of them contained in two Northeast quadrant girders), we would be forced to go beyond anything we had done before.

Several areas of Menokin were enclosed with plexiglass scribed to the remaining walls in order to temporarily protect the fragile interiors while overlays gave indication of the possibilities for glass.

But why try to make a “herculean effort” to save damaged timbers?

If this sort of herculean effort to save original material had not been ongoing in sculpture, furniture and the decorative arts, we would not still be able to enjoy Michaelangelo’s David or the Mona Lisa. If the task before us today was to save a van Gogh, there would be no question that we could find a way. As a society we could not fathom the loss of so authentic an experience. Whole buildings are much more complex than any single work of the decorative arts. They therefore demand integrated approaches and cross-trade skills.

When confronted with the real thing, even by novices, authenticity in buildings is equally felt.  But buildings are at far greater risk, being the vessels in which we live and work but for which we generally have little regard.

Only a low to moderate strength polymer is needed for strengthening and toughening most deteriorated wood surfaces since most deterioration in wood is on the surface and leaves solid, strong cores. But with Menokin we needed to approach strengthening the system by cushioning individual weakened members and supporting loads over a larger area using materials that could be replaced, removed and improved without destroying the original artifact.

To this end, we began working with Chemist Richard Wolbers on a new consolidant – using dibasic sugars – and the initial small tests were promising.  Dibasic sugars rebuild cellulosic polymers in the airspace of timbers. (Void spaces are 60% of any sound timber, hence wood is relatively light and rotten timbers have even more void space). As the solvents evaporate from a 1-2% dibasic sugar concoction, the structural sugars begin to self-form onto the existing cellulose in the wood. Small laboratory tests contributed to a 400-500% increase in compressive strength in weakened timbers – and these long-term compounds appear to be reversible in practice, not just theory. The next stage was to scale up testing larger elements and working out delivery systems.

Our interest in carbon fiber also came out of discussions with Richard about the long-term stability of epoxy resins. Initially I was thinking in terms of buying CF planks, beams, strips, etc and attaching the damaged elements to or around timbers. But as I researched more, I realized CF cloths lend themselves infinitely to forming and shaping and that we might be able to laminate and vacuum bag them to any shape. (Again this goes back to a principal of preservation: fitting the repair to the original; not the other way around.) I purchased a variety of CF woven clothes and vacuum pump resin delivery tubes, release fabrics, sealant tapes and begin experimenting.

In the next post we replace the center of a hollow timber with carbon fiber.

Click here to learn more about the big plans the Phillips-Lee-Macfarlane Team developed for the “Visible Building” version of the Menokin Glass House that would return original timbers and decorative elements from storage to their original locations while providing elegant integration of informational glass, solar, and low-tech passive heating and cooling.