Carbon Fiber Repair Options for Historic Buildings, Intro

Retrospective: Timber Conservation to Date 

The following is our 2007 introduction to timber and masonry strengthening approaches we were investigating for the Menokin ruin in Warsaw, VA. At the time we were just completing the first phases of extraction and cataloguing of fallen elements from the basements. And we had just done an 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.

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. With this document, we were introducing him to the next stage in our thinking about the project which would include the glass and original walls providing the support for reintroduction of damaged timbers to their original location and function within the building. To do this, we needed to review the current state of timber conservation and explain how we were trying to take it to a new level for this project.


Menokin Glass House

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

Charles and I have been developing and trying to improve techniques from one project to the next over the last thirty years across a variety of materials, including less-invasive repairs to structural timbers. I thought it might be useful for you if I gave a little retrospective and reflection on the evolution of the process over the last thirty years.

The beginning of the “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 now too often  was to tear the entire element out even though the damaged part 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 really means the architect is off the hook with the Secretary of the Interior’s Standards and the contractor can do whatever he thinks it means. 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.

Under the best circumstances, repairs augment the original without destroying them. Much of this is basic stuff, for instance increasing strength (pull-apart) 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, for instance the intersection of elements in a roof or bridge truss.  Then there were 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 system  works.

In my experience,  this sort of practical method rarely happens and I’m afraid less so with each passing year. Thirty years ago, preservation using modern materials and techniques was the norm. 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, or more often, make lots of rash assumptions and throw additional structural supports at perceived problems (surface conditions) without addressing the underlying faults. The consideration that most seems to drive projects is that the system look sound and neat (pristine) in a sort of Disneyland/Hollywood slickness that is the opposite of authenticity.

From the first time I began working on old buildings in 1973, I have continuously worked to make repairs as unobtrusive as possible. This invisible mending approach came from the prior six years of apprenticeship in cabinetmaking and 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. So 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 was weakened by fungal attack and weathering or painter’s scrapers, but was otherwise largely intact.

Epoxy resins seemed perfect for the problems of buildings. Often the tooled surfaces created by the artisan several hundred years before were intact, although often only held together by many coats of hardened lead paint. Epoxy resins soaked into the soft cellulose fibers, where they cured, providing 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 exemplified by the three tenets of conservation – predictability, compatibility, and reversibility – the watchwords of this new field that recognized   buildings as important artifacts that should be treated as we did objects in museums. We should not be the last people to experience these buildings in their original configuration and materials. So to be good stewards, we were trying 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 them to rely completely on off-the-shelf products and cure-alls supplied by a burgeoning and mostly cynical and unscientific “restoration products industry.”  I guess this is 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 stainless 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. So 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.

AIC X 3-6

The floor joists treated with this method at Londontowne are a good example of this hybrid approach. The exterior shell of the joist is toughened without any change in appearance. Then a new core of ¼” stainless steel carries the load to a ledger placed in the brick wall. A wood spline filled the slot for the steel 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 and was completely invisible to visitors.

LT-Joist-031   LT-Joist-029   LT-Joist-030

So this approach is 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 they 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.

Now comes Menokin. I have been visiting Menokin for twelve years since the foundation first gained control of the building, through its continuing collapse and dismantlement to the Board’s realization 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. I have believed all along that the original building can 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 saying “We work on the pieces and they work on us.”

We have been going back and forth reevaluating existing techniques and trying to imagine better ones. One side says let’s do very sophisticated furniture-type repairs subtly distressed so they repairs aren’t 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. And they make you proud.  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 sculptures and blocks. These explorations and discussions have continued for several years and have 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 ruin and realized it had a good chance of succeeding, we decided it was time to move to the next level of conservation techniques. As you know, we believe there is 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 can develop a proven methodology to elegantly reload the joists, then we have the methods for saving the rest of the building. By starting with some of the most difficult problems (nearly all of them contained in these two Northeast quadrant girders), we are forced to go beyond anything we have done before.

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. We could not as a society 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 integrate approaches and cross-trade skills. I believe 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.

We need only a low to moderate strength polymer for strengthening and toughening most deteriorated wood surfaces. Most deterioration in wood is on the surface and leaves solid, strong cores. Consolidants must not change the appearance of the treated area and, again, must actually be reversible. We need to approach making things strong enough by cushioning them and supporting loads over a larger area using materials that can be replaced, removed and improved without destroying the original artifact.

To this end, we have been working with Chemist Richard Wolbers on a new consolidant – using dibasic sugars – and the initial small tests have been 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 tests in the laboratory have 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 is 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 them. 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 (see  photos). I’m in no way saying I have answers here, just some starting ideas and a lot of questions and experiments I want to try.”

In tomorrow’s post: how we replaced the center of a small section of hollowed-out timber with a carbon fiber core. Click here if you are interested in better understanding the big plan for the Menokin Glass House and its re-incorporation of original damaged timbers back into the building.


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