Foundation Wall Rx

Q: What can I do about the deteriorating layer of mortar plastered over the exposed part of my basement walls? I live in a 13-year-old brick bungalow, with about 6 feet of concrete block foundation visible above ground. Over the years it’s become messy looking, with faint concrete block lines and damp spots showing through. Can this plaster be replaced? Is it a good idea? How much would it cost?

A: The stuff you’re worried about is called parging: a thin, plaster-like coating of cement-based mortar that's often applied to exterior blocks and other foundation walls to make them look better and last longer. Trouble is, it usually starts to look pretty bad in time. The symptoms you describe are actually quite mild compared to how bad things can get with some parged block walls. It's common to see large flakes of mortar falling off, and it's only a matter of time before this happens at your place. The good news is that your situation isn't that bad yet, so a good-looking, remedial repair is definitely possible. The first thing to understand is that moisture is the enemy. It soaks into some types of masonry and freezes in winter, causing mortar, brick and block to crumble and flake. Since this sort of mechanical damage hasn't yet happened to your house, prevention is the best course of action. Although you could treat the parging with industrial strength masonry water repellent, paint would look better and work just as well. Your foundation wall is large and plays an important visual role in your home’s appearance. Exterior paint, especially 100% acrylic latex formulations, are very durable, effectively sealing out moisture and hiding block lines and damp spots you describe. I'd pressure wash in the spring, let the walls dry, then brush on two or three coats of the highest quality exterior latex you can find.