Brick Repair: The Hard Facts
Watch a video on slaking lime at Virginia Lime Works
If you have a brick house or masonry wall to maintain, you need to know a few things in order to properly restore it and keep it in tip-top shape. We’ve all seen masonry repairs that detract from the integrity of the house. A few simple things will keep it from happening to yours.
For example, some houses look completely different after the bricks are re-pointed. The mortar is a different color and the mortar joints are larger than they were originally. The beautiful patina of the aged bricks is gone. How can such a stark change be explained?
First off, it is very important that the replacement mortar is compatible with the historic mortar. Incompatible mortars can cause irreversible damage to historic brickwork, including spalling (deterioration of the brick themselves), cracking, and interior mortar rot. The same problems can occur when an incompatible stucco or paint is applied to historic buildings.
Traditional mortars - such as lime mortar - allow historic masonry to breathe and move, giving new life to historic masonry. The work can look unattractive, but as long as you are using good materials, you’re not causing additional problems. Then again, you can have attractive work done with bad materials, which will cause problems. Of course, in a lot of situations you have a combination of incompatible materials with unsightly craftsmanship. That is bad news all around.
Jeff Price of Virginia Lime Works stresses the importance of matching historic mortars. To do so, he suggests matching the color of the interior of the mortar sample. This way, you match a surface that has not been exposed to the elements and other environmental changes. This may mean for a while the mortar looks slightly different, but over time the color will "catch up" with the existing mortar. If the new mortar is matched to a "dirty" color and the building is ever cleaned, the old mortar may look pristine and the new mortar will still look dingy.
On the subject of environmental changes, we often find traces of a "treatment" to historic masonry in the form of either colorwash, penciling, stucco, or limewash. Each of these treatments,--called "skins" -protected the host masonry. Often they are viewed as decorative finishes, but they were functional as well.
Colorwash is commonly found on masonry. This mixture of potash alum, water, pigment and glue (melted animal hide such as rabbit skin) was similar to the fixing agents used to dye wool. Colorwash was used add a protective layer for the softer lime mortars, which take more time to cure. It was also decorative, clearing up any mortar stains or smears that may have been left on the brickwork prior to the introduction of masonry detergents.
Penciling is a mixture of chalk, glue, and water often painted over the mortar joints (both with or without colorwash) to add a layer of protection to the walls. If there is a slight yellowing of the coating on the mortar joints, this could be due to either the incorporation of linseed oil in the penciling material, or the use of linseed oil painted over top of the penciling to add a level of water shedding.
Stucco is a coating that offers a more substantial coating that a wash or paint, and can be highly decorative. Before 1900 stucco was often a mix of lime and sand. Frequently stucco was ruled out or "scored" to give the appearance of cut stone. It’s quite common to see stucco (or the traditional term of "rendered") with a coating of Lime wash.
Limewash is mixes of lime and water, with or without admixtures to make it more durable. Some of these additives include salt, blood, and milk. Limewashes and lime paints were found on both rendered and bare buildings to provide a level of protection to the masonry.
Jeff attributes those large, sloppy mortar joint obvious on bad repair jobs to one of two things: one) filling out the mortar too far, causing a 3/8" mortar joint to appear more like a 3/4" mortar joint; or two) using an angle grinder to cut out mortar joints. To repair the former, he recommends leaving the mortar contained to the mortar joint and finish it to just 1/8" of the face of the masonry. For the latter, if you find it necessary to remove historic mortar by mechanical means such as a grinder, the mortar is most probably performing satisfactorily and should not be touched in the first place. If it is Portland cement (in the form of a later repair) that needs removal and it is deemed necessary for the use of a grinder to do the job, only use a blade that is less than half the width of the joint (i.e. 3/8’ joints the thickness of the blade would be less than 3/16").
Unfortunately, it is all too common that a grinder is used haphazardly and takes out not only the mortar, but also the tops and/or bottoms of the brick as well, causing a nice tight 3/8" joint to become 1/2"-1/4"! This irreversible damage causes the historic masonry to forever be changed.
Sometimes paint has a tendency to bubble up on the inside of plaster walls. At first, you’re apt to think that this conditions means that moisture is penetrating the brick walls and the wall is in need of re-pointing.
More than likely, according to Jeff, it is not due to re-pointing. Rather, it is a sign of moisture in the walls. Historic masonry is breathable. It allows moisture to travel through the masonry and either return through the semi-porous masonry exterior or travel completely through the wall and dissipate through the interior plaster. When a common paint is used to finish traditional lime plasters, this breathability can be inhibited causing moisture retention and the paint to bubble. The best way to prevent this happening is by using a traditional paint such as a distemper or limewash.
Excellent example of creative, quality craftsmanship from the past.
If your walls do need re-pointing the main thing to keep in mind is that you don’t want to change the character of the exterior brick.
In this case, Jeff suggests first looking-really looking- at the building. Take a survey and check out the various details that make your house unique. Check for the original joint details (such as overhand struck joints, bird’s beak, double struck and ruled) in order to determine the way the masons finished the mortar joints. Follow this technique in any new work. This will help keep things look great. Check for colorwash/penciling/stucco/limewash, all of which are things that may have been removed or worn away over time.
If your brick house was painted some time in the past, pay attention to how it is repainting. Paint can affect the longevity of the brick and mortar. Often the use of a latex or other modern paint coating can hold moisture causing the mortar and brick to retain moisture. The moisture may freeze, causing spalling and failure of the host masonry.
Jeff recommends stripping old paint off the house before re-painting it. Although some paints will cover and coat modern latexes, the problems will remain under the surface. It may look fine, but the mortar won’t perform as it should.
Replacing Missing Bricks
Lastly, it is not uncommon with old masonry structures to have damaged or missing bricks. If that’s the case, check with architectural salvage companies that reclaim brick from demolished historic structures. Also, many masonry supply houses offer a wide variety of brick products such as hand made brick made in the way they have been for centuries, with unique faces with folds, creases and irregular corners. They offer a range of colors and shades. In short, it shouldn’t be hard to find new brick that blends with the old.
Editing and photography by Maurice Duke