Is it going to be rebuilt, restored or preserved? When you start discussing work on old buildings, that's the first question to consider as the approach you take can vary greatly.
"Preservation strives to use, to a greater degree, the original materials more then compatible materials in terms of strength and stiffness," notes Michael Schuller, president of Atkinson-Noland & Associates (ANA) of Boulder, Colo., one of the foremost international authorities on both modern and historic masonry structural systems. "In restoration you are trying to bring a building back to how it looked in some point in time. It is considered permissible to replace original materials with new material that looks the same. It doesn't have to have the same formula, for example. You can fix spalls if you have a damaged stone you might actually build that up with some new materials to match the original profile."
Preservation is a slightly different approach in that you are trying to maintain the original materials as much as possible without necessarily making it look like it did years ago. As Schuller says, "That might involve some of the same tasks that you are involved in with restoration but to a lesser degree. So if you have some stone that is deteriorating on a building that you are restoring, chip away the damaged stone and build up the rest to the original profile. From a preservation stand point, if you are involved in a historic preservation project, you may not want or be allowed to introduce some new materials to get rid of the damaged material. You may apply some water repellent or something to slow down the deterioration process but not necessarily add a lot of new materials."
Schuller looks at the situation as an engineer. "When you do work on buildings that are one hundred or two hundred years old it's a little different mind set than designing a new building. One aspect is just the evaluation phase, figuring out how the building was built originally in the absence of drawings and details and finding out the kind of materials that are there, the engineering properties of those materials. It's like ‘reverse engineering' the building. I see a lot of companies coming in that do modern masonry and when they get involved in older buildings, they aren't used to the lower strength of material that we had a hundred years ago. Maybe there has been some deterioration, some things that don't have much strength, and so the immediate reaction is always to replace those materials with something modern, strong and stiff but that can actually be more damaging and could do more harm than good."
You have to consider the old theme of "weakest link in the chain." By using stronger, stiffer or more resistive materials, you change the flexibility of the building and relocate the stress points. That can cause a shift in the natural dynamics of the structure and fight against the architect's design and engineering.
Schuller explains, "When we are dealing with a historic building, we try as hard as we can to get a material that matches the materials in the building. I'm getting at the whole compatibility concept: if the new material doesn't match the original in terms of strength and stiffness, we can get some strange stress distributions in the future."
Most preservation groups strive to maintain historic buildings in the way they were built, adding in the aging factor. Slowing deterioration is a major ideal; making the building look like new isn't. On the other hand, restoration groups want to return old buildings to the state they were in when new, or when they "became historic." So a preservationist wants repairs, for example, to use similar methods and materials. After all, if you can get the materials reproduced, the techniques can be matched many of them haven't changed in 200-300 years, right?
Ah, getting the materials ... that can be a problem. Linda Evans, president of Stone Arts in Church Hill, Tenn., is one of the experts on preservation and restoration masonry materials. Stone Arts replicates bricks and blocks using materials as close to the original used in historic buildings, including following the sometimes-ancient methods of making those bricks.
"Some of the chemicals that were used in old brick, such as chromium, are not friendly materials to be around and I tend to stay away from those," admits Evans. "I'll find something else that gives me a similar look. We get pretty creative sometimes because we might not know how a brick was made, or exactly what was in it, or even where the clay came from. I can get clay bodies from most of the major manufacturers, sometimes in the form of large plugs so I can cut out whatever size is needed and add whatever slurries, metal and iron spots, and things like that to make it look like the original. We can over-fire and under-fire, and fire rapidly to cause a bloat."
Sometimes, making bricks for historic preservation means making them wrong. "We actually had a building where all the bricks were bellied out. They looked like little loaves of bread in the wall. These brick had been laid up on their edges, instead of on their beds. The bricks were manufactured to be laid down flat and they turned them up on the edges so that the bellies stuck out. This was a manufacturing faux pas. It became a historic building. It outlasted all its neighbors and they needed some more of these bricks that were basically mistakes. The clay had high carbon content and if you fire a brick with a high carbon content quickly, it will bloat or swell, rise like a loaf of bread because the carbon cannot burn off fast enough. So not only are we duplicating good brick, we also duplicate mistake brick."
One of companies using Stone Art's matching services is Bri-Den Construction, a firm doing work on Carnegie Hall in New York City. According to Bri-Den's Joseph Blesi, the company is adding a ticket booth and remodeling the entry, matching the terracotta and brick of the original Hall. He says they have had to do some cleaning of existing brickwork under the close eye of the preservation people who are overseeing the restoration. Samples were done at out-of-the-way places to show the effect of various cleaners and methods before the go ahead was obtained.
Matching the bricks was another critical area that had to pass muster. Evans recalls, "We provided 5,000 bricks for Carnegie Hall. It was a buff colored body in a roman size, which is a long, skinny brick, like 1-1/4 inches tall and 11 inches long. It was an ‘iron spot' that had a lot of metal in it that had blistered through the surface as it was fired. It was interesting to duplicate the texture and finish as well as the color, and in a size that isn't available any more."
Hiding Modern Technologies
Last year, we reported on the rebuilding of the Pentagon after the September 11, 2001, attack. That building, like so many in Washington, is covered by the District's Historical Society. But instead of preservation, they knew they needed new engineering to increase the protection afforded the thousands of people who work there. That caused a dichotomy: improve the building making it more blast resistant, for example while maintaining the historic look. For example, the new windows are designed to withstand explosions nearby, but they incorporate the same hardware designs as the originals. That includes small features like the window screen retaining tabs, although the new windows can't be opened and will never have need for screens. The ornaments make the windows look like they did in 1940; the engineering and materials make them adequate for the 21st century's concern over terrorism.
Another behind-the-scenes improvement, which is being used on other D.C. historic buildings, is increasing the insulation of the structure. AC&R Insulation, Bethesda, Md., is doing work on Washington area buildings. Ginny Cameron, AC&R's president explains, "Some of these old buildings are very inefficient but the nice thing about them is that many times they have a very, very large wall cavity that makes it easy to fill and then you get a very good ‘R' value. Many are of the old construction that didn't use a plate at the top of the ceiling so you can run a hose down into those cavities and you can fill them up with insulation to make them energy efficient. And the nice thing is, nobody can see it. It doesn't change the appearance of the building."
AC&R is using Polymaster foam insulation pumped into those cavities. "You don't have to worry about removing plaster, removing the ornate moldings; you only have to make an access hole and put the insulation in and you are all done. The last couple jobs that we've done, the [preservation] society asked if there was anything we could do to make it more energy efficient. A lot of times they will try to get a new window that is an energy-efficient window but that look like the older windows. I think that's a much more difficult process then insulating the wall and you save more energy insulating the walls than changing the windows anyway."
Hidden away inside the walls, the foam doesn't change the look of the historic structure but improves its usability. Dave Russell of Polymaster, Knoxville, Tenn., adds, "There are all kinds of old, masonry buildings that don't have any insulation in them. There is a fast growing application of polyurethane foam where it is being sprayed on the exterior of masonry block before the brick goes on. An inch of it is R7-plus it's self-adhesive and a two pound density foam and higher. It is even a damp proofing material so it's a one-step insulation and ‘damp proofer' for new or old buildings."
Atkinson-Noland & Associates has done work on material that can improve seismic resistance while maintaining the historic look of a building. "We were very involved in some research for the National Science Foundation back in the early nineties looking at seismic damage," comments Schuller, "and one of the techniques was grout injection. That turned out to be a really useful procedure and is used now to repair cracks and voids in walls by introducing materials into those cracks and voids."
Schuller says, "We've been working in Baltimore for about ten years using this process to repair buildings a low-pressure process where the grout goes in at something like eight or ten PSI and it's injected into small (a maximum of one-half inch diameter) holes drilled in the mortar joints. It requires special grout material. Our job for historic buildings is usually to come up with a grout formulation that, believe it or not, is relatively weak compared to modern materials but it does harden inside the wall. Most of them are cement base, lime and some other materials. Essentially, we try to match the mortar that was originally used in the building as closely as possible."
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