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Pamela Bates received the 2011 the Peter H. Brink Award for Individual Achievement from the National Trust for Historic Preservation – announced in the Preservation Magazine November/December page 46. I was inspired to read her commitment to the Lowell’s Boat Shop in Massachusetts, the oldest continuously operating boat shop in the country founded in 1793.
Through its different ownerships and threats by big developers – for the prime waterfront property, the building survived after Bates assembled a coalition called Lowell’s Maritime Foundation which purchased the landmark. The nonprofit took ownership in 2007 and has operated Lowell’s ever since.
What I think is most dynamic about the preservation plan is it includes building wooden boats, a well-kept secret, in a working museum setting. People can actually go there and watch boat building in progress. I believe the best museums are the working museums – full of life, just like the old days when business was booming in the 1700s.
Today, I acknowledge Pamela Bates for her inspiration, patience, and preservation energy. Congratulations Ms. Pamela Bates and to the National Trust for selecting a great candidate for the Peter H. Brink Award for Preservation. I hope to someday visit this property in the future and hope you will too.
Lowell’s Boat Shop: http://www.lowellsboatshop.com/pages/pressmedia.html
Mortar analysis can be done various ways with several different approaches to identify the original mortar ingredients of a formulation. However, there are limitations and replacement mortar specifications should not be based solely on laboratory analysis. Analysis requires interpretation, and there are important factors which affect the condition and performance of the mortar that cannot be established through laboratory analysis. These may include: the original water content, rate of curing, weather conditions during original construction, the method of mixing and placing the mortar, and the cleanliness and condition of the sand (Pres. Brief 2 pg. 2).
Mortar can be evaluated by simple wet-chemistry of using hydrochloric acid and water to dissolve out the binder components (calcium carbonate) leaving only the sand particles behind. The ratio of binder to sand can be determined by drying the sample first then weighing it before and after the wet-chemistry process. The problem occurs when calcium carbonate is part of the sand component which would give you a false reading of the ratio. There is also x-ray diffraction, and petrographic analysis by microscope, as well as thin-section technology, where small samples of mortar are cut into very thin sections and dies are injected into the sample showing the different components of the mortar. In addition, ASTM C1324 is a test method to determine components of hardened mortar samples.
The most useful information that can come from a laboratory analysis is the identification of the sand by gradation and color. This allows the color and the texture of the mortar to be matched with some accuracy because sand is the largest ingredient by volume.
A simple non-technical evaluation of the masonry units and the mortar can provide information concerning the relative strength and permeability of each-critical factors in selecting the repointing mortar – while visual analysis of the historic mortar compared to the new replacement repointing mortar can be made. It’s important to match the un-weathered portions of the historic mortar in case the building will be cleaned in the future, or cleaning should be taken into account before the sample is matched.
Part of the solution to the problem of moisture migration is allowing the water to have its way. In above grade walls, that means letting it go through the wall, then redirecting it through flashing and weep holes if possible, and most importantly, using a breathable mortar that is more porous than the brick or stone.
Below grade, keep water from resting on the outside of the foundation walls in saturated soil conditions. Create a drainage system, a way for the water to move away from the foundation, perhaps installing perforated foundation tile at the base footing of the wall with gravel fill. Again, check gutters and downspouts to ensure they are clean and take water away from the wall, extending downspouts at least three feet past the elbow at grade level is a good idea. Grade the soil and pavement materials around the building to encourage water runoff and avoid collecting and pooling near walls.
Detecting trouble in advance – The use of a moisture meter can sometimes be helpful in determining a baseline for acceptable moisture content in a historic masonry walls. Because not all masonry walls are created or built equally, all have varying levels of moisture depending on conditions. What is important in establishing a baseline is looking for the wall sections that are performing well. In these areas, take readings to compare to areas with deteriorating brick or stone. This will put you on a specific path toward understanding what to expect in the future.
Also consider choosing breathable mortar materials like lime putty or hydraulic lime blended with coarse aggregate particles – often the vary material that has turned to dust over the past 100 years. Do not try to make it stronger or better. Just match the old lime mortar and move onto the next project. If the original historic mortar has turned into dust or is falling out of the wall, it is likely a lime mortar. It has done the hard work of absorbing more water than the brick over and over again and now needs replacement. The brick or stone is generally preserved in these cases.
The new lime mortar replacement mixture should match the old mortar and perform as the old mortar did – it to will turn to dust and fall out of the wall in the next hundred years, giving the next generation something to fix.
Lime Putty Suppliers in the US:
U.S. Heritage Group, Inc.
Virginia Lime Works
Hydraulic Lime Suppliers in the US:
U.S. Heritage Group, Inc.
Virginia Lime Works
Capillary suction in foundations is often called rising damp. Evidence of the condition is commonly found inside the basement, and in more advanced cases, outside too. Rising damp will often leave behind a tidemark on the wall surface. In areas subject to freezing, the condition can cause spalled masonry units and failed mortar joints. Broken downspouts, clogged gutters and underground sprinklers contribute to the condition, as will soil heavy with clay.
In the late 1800s builders and architects generally would select masonry materials that had a lower porosity for the first few courses of foundations in an effort to manage moisture from rising. Many government buildings in the United States have granite incorporated into the design of the building foundation, and then sometimes a course of slate tiles in the bed joints between the masonry units to offer additional protection. This design would mitigate the rise and force the water back down into the foundation wall from where it came. Under total saturated conditions, with nowhere to go the water could find its way out the face of the masonry units and mortar joints either indoors or outside, deteriorating the materials over time.
Water can cause trouble by itself, such as when it is exposed to freezing temperatures. But when water is combined with salt the trouble is magnified many times. Pressures build inside the wall system when salts try to dry out and crystallize, making for an eruption of spalled and deteriorated masonry. Osmotic pressure is caused by expanding salt crystals trapped in the body of masonry formed during and after the evaporation of water on the surface. It is these salt crystals that appear as a white powder on the wall. They can potentially build up to 3,000psi, stressing the masonry. This condition can be compounded up to 5,000psi when past attempts to control the moisture by repairing with hard mortar and applying spray-on waterproofing materials are involved.
As promised from yesterdays post we were going to take a look at how water enters a building. We know water can enter a building in many ways, through masonry walls, roofs, windows, and saturated soil surrounding the foundation just to name a few. There is also interior sources of water, such a condensation from cooking, cleaning, showering – generally occupying the home. However, this is not the whole story when it comes to historic masonry walls. What we don’t talk about much is the “embodied water,” the water that remains in the walls at all times. Old historic masonry walls are moist in the center, due to the porosity of the masonry units, the lime mortars, and the thickness of the wall – it’s just hard for them to dry out completely. They really never do completely dry out, especially if they are foundation walls. We must consider this condition and account for moisture already present within the wall, because if we don’t, we could unintentionally trap moisture even when the outside of the wall feels normal and dry.
Load-bearing historic masonry walls (16 inches to 24 inches in thickness) are porous, capable of wicking large amounts of water great distances due to capillary suction. The smallest cracks and pores found in mortar, brick and stone can bring on water in a big way. The action of wicking is energized by the horsepower of smallness. The smaller the pores or cracks in the wall, the more powerful the draw of the wicking action. If you have given blood, you may recall the very small glass tube the nurse uses to take a droplet of blood from your fingertip with a seemingly invisible vacuum cleaner. The blood droplet instantly goes up the tube – effortlessly, capillary suction at work.
The horsepower of smallness regarding the capillary action of water should be cause for concern, because architects and contractors are often focused on repairing large cracks in buildings while leaving the small ones untreated. Don’t be deceived. The small cracks, even the hairline cracks, are where the suction power is. One way to slow down the power of capillary suction is to reduce the surface area of the material that comes in contact with the water source. For small hairline cracks, injecting dispersed hydrated lime (DHL) into the crack with a syringe will sometimes do the trick. Unlike epoxy or cement, DHL remains flexible after it cures and maintains good vapor transmission, allowing the wall to breathe while at the same time halting the water – pulling the plug on the vacuum of capillary suction.
Dispersed Hydrate Lime (DHL) is a product imported from Germany and has been used successfully on many historic masonry structures here in the United States for over 10 years. Information on the product can be obtained by contacting the U.S. Heritage Group based in Chicago. Other vender choices I’m sure are available, but this is the product we have specified and are most farmiliar with using.
SPC Training video on DHL injection: http://www.youtube.com/user/SpeweikPreservation?blend=4&ob=5#p/u/4/mlGm2XvEGF8
The new term on the streets used by industry consultants to describe the details of how a building takes on water and then (hopefully) sheds it is “water management.” The longevity of historic masonry walls relies heavily on how water is managed in and around them. I am personally not yet convinced we can control water. I can work to manage where it goes, and possibly how long it stays – by redirecting it, but in the end it goes where it wants, the easiest way. When you attempt to fight water it usually wins. The ways water impacts a building depends on how long it stays – which is directly correlated to its architectural design, geographic location, topography, soil, the water table, the type of brick, stone or mortar, and whether the building has recently been restored.
Sometimes the understanding of historic load-bearing masonry walls built with lime mortar materials is not established, or respected, prior to a restoration project being undertaken. While the joints may look like they are in need of repointing due to deterioration, it’s important to know why they deteriorated in the first place. The cause is most likely from water saturation – then freezing and thawing or extreme temperature variations. One of the challenges is understanding that a building can, and does, breathe though its mortar joints as well as its masonry units.
The shear thickness of most load-bearing masonry walls keep the water out. The original building materials made for quick evaporation of the water on the surface of the walls and kept the inside dry, but this breathability does takes its toll on old lime mortar joints and they need to be repointed in high moisture areas every 75 to 100 years or so. Problems start when an architect specifies a replacement mortar that is harder than the original (in an effort to make it last longer) than potentially traps moisture inside the wall system. The effort in the restoration repairs is totally focused on keeping water out from coming in through the exterior side of the wall. The problem is that old masonry walls contain a certain amount of moisture already and often do not perform very well with harder/stronger mortar joints surrounding them.
When the goal of the restoration project is to create a Watertight Envelope you’d better run the other way – fast. “Watertight Envelope” and “Historic Load-bearing Masonry” should not be used in the same sentence. Keeping water on the outside would seem to be an honorable goal for any restoration project, but observing the current condition of some masonry buildings restored in the past 10 years tells us a much different story, a troubling one. Basically, the buildings subjected to this watertight-envelope theory are not doing very well.
Where waterproofing and harder cement-based mortars are applied we find decay patterns that are surprising – in just a decade after application. Instead of the mortar surfaces wearing, there is a new pattern of brick and stone decay. Strong osmotic and hydrostatic pressures build up in brick and stone that are subjected to these hard, strong, and water resistant materials.
Tomorrow we will discuss how water enters a building.
Building materials crack for different reasons. In some cases it could be a material failure of the individual masonry unit and not associated with the wall assembly. But in most historic masonry loadbearing walls the cracks have something to do with thermal change and or ground movement or possibly a water related issue dealing with the foundation. Either way cracks must be repaired to prevent water from penetrating the structure and causing further damage.
There are many different types of crack repair products on the market today. Basically they break down into two main categories 1) ridged repair or stitching the masonry units back together – for example, epoxies would be in this category. You would use epoxy material when you are repairing an individual masonry unit like a piece of terra cotta damaged from a wall anchor or manufacturing defect.
The second category, and more common, is that of a movement crack, or a dynamic crack, that changes its width and dimension during the change of seasons and under different weathering cycles and building movement. These cracks are generally continuous and follow a distinct pattern from the ground level through to the top of the wall and often through the entire width of the masonry transferring on the inside of the wall surfaces. A crack like this would need to be repaired with something other than epoxy.
Because experience has taught us that if we inject a movement crack with epoxy – another crack will likely appear 6 to 8 inches on either side of the original one – as the building still moves in this location. A better choice of materials like a dispersed hydrated lime (DHL) injection material, or a flexible injection grout, one that accommodates movement would be the best material to specify in these areas. These materials seal off water infiltration while at the same time allow the movement to occur naturally.
It is also helpful to establish how much movement you have on elevations by the use of crack gauge monitors. These monitors allow for the periodic measurement and evaluation of the crack at different times of the weathering cycles. It is best to know as much there is to known about your building problems before material specifications are finalized to be sure you have the right material for the right treatment.
Training in Application: http://speweikpreservation.com/2011/05/22/training-dhl-dispersed-lime-injection/
I attended a social networking gathering at my wife’s college last week. The university has an architecture program with an emphasis on sustainability. I was introduced to one of the students a “MArch Candidate” it said on his business card. I mentioned I was involved with historic preservation of traditional architecture and his eyes lit up.
His young energy filled his mouth with words of interest, but I truly knew he had not a clue what I did for a living. We exchanged pleasantries and he mentioned sustainability as one of his schools focal points, and his as well. I discussed my specialty in Division 4, Historic Masonry, and followed it with the statement that preserving architecture is the ultimate sustainability.
When you stop and think about it for a moment, it really is something.
The brick are already fired, no need for fuel or manpower to extract the clay from the earth – already done! Same goes for the stone – already quarried to size, and transported to the site – lifted into place. The mortar ingredients have already been located, sifted, fired, mixed, and installed between the units.
All the collective energy and labor effort in Division 4 has been paid for and is waiting to provide more life-cycle performance to the next generation – for perhaps another hundred years. With the right preservation plan for its reuse you have sustainability at its finest.
The building boom from 1880 to 1900 opened a new door in the chapter of material specifications. Steel rail producers and steam engine builders who began using Bessemer steel could no longer rely on craft experiences of centuries past. New technical expertise was required.
Several large steel producers in the United States attempted to implement their own ideas to produce better steel, but these efforts never made it into the marketplace. The added cost to produce better steel products was thought by the management of these large companies to not be worth the price of losing market share. As a result, continued to produce large quantities and low prices, believing this was what the customers wanted. Not surprisingly, numerous quality problems with steel rails came to light though independent investigations into derailments. In fact, American steel rails were so poorly made that many railroad companies preferred British imports, which were far more expensive but much more reliable.
It was clear something had to be done. Some type of standard material specification was needed. Progress was nevertheless very slow in coming. Manufacturers in the construction industry objected to standards material specifications and testing because they feared that placing strict quality controls on products they produced could make customers more inclined to reject items and default on contracts. Material standards were thus not well received and remained very controversial.
In a creative effort to overcome antagonistic attitudes towards industry material standards, Charles Dudley, a research chemist working for the Pennsylvania Railroad, suggested the formation of working technical committees to discuss testing methods and approaches. He further suggested that decisions on standards be based on a consensus process. Dudley’s ideas were finally embraced and the American Society for Testing Materials (ASTM) was chartered in Philadelphia in 1902. In its bylaws, ASTM dedicated itself to “the development and unification of standard methods of testing; the examination of technically important properties of materials of construction, and other materials of practical value, and also to the perfection of apparatus used for this purpose.”