When I'm listing , selling, and dealing with historic masonry homes, many times owners will have areas of brick, stone, or concrete that are dirty and stained from rain, leaves, dirt, and other elements. It seems like many think the best way to clean them is by hiring someone to come in and powerwash before putting house on the market. When they ask me, I usually have to explain that powerwashing historic masonry is one of the worst thing you can do. Many homes back then used lime mortars which are soft, and a pressure washer will blow the joints out. When that happens, they will need someone to come back and point up the joints that were blasted out. That lime mortar should be replaced with matching lime mortar, not the standard type N and S mortars that are common today. Also, many of the bricks are softer, and the pressure could damage those as well. Concrete is really the only thing I would consider pressure washing, but it isn't always required.
I've cleaned and restored many historic homes over the last 35+ years. I have also cleaned and repaired several historic monuments and many gravestones, including some at Arlington National Cemetery. The main cleaning product I use on historic masonry and gravestones is D2. It's also the preferred stone cleaning product of the National Park Service. D2 is a biological solution, and contains no salt, acids, or bleach. It's safe to use around plants and wildlife.
Below is a test I just did on a set of front brick steps. It was raining, but the test still shows what a little D2 will do. I sprayed some on this center brick, waited 5 minutes, scrubbed a little with a soft brush, then rinsed. ( never use a wire brush, especially on gravestones). The D2 will continue to clean for weeks, and everytime it rains, this brick will get cleaner. You actually don't have to scrub at all. Just spraying D2 on steps like these is all that is needed, cleaning will occur naturally over time. In this pic, the center brick looked just like the bricks on both sides of it. After 5 minutes with D2, almost all the black stains are gone. In a few days, it will look even cleaner. It works well on mortar joints as well. No pressure washing is needed. You can learn more about D2 and where to buy it here: http://www.d2bio.com/
Jeff Pearl | Lic in VA
Homes | Land | Farms | Historic