Q: I live in a townhouse where brick surrounds the base of the house. This year, I’ve been finding that the outer surfaces of some of the brick have been peeling off. What is causing this? Does it affect the integrity of the brick? Is there any way to prevent the peeling from happening? Do the bricks need to be replaced? If so, what type of person would do this work?

A: “Spalling” is the term for what you’re seeing. It happens when bricks absorb moisture, then freeze before they dry out. Water, like most liquids, contracts as it cools. But when water reaches about 39 degrees, it expands slightly as it reaches freezing temperature. As it turns to ice, it expands even more — up to 9% — because of the structure of its six-sided crystals. This expansion is almost certainly what is causing chunks of the bricks to pop off.

You note that the bricks surround the base of your townhouse. This type of brick treatment is typically just a facade: a decorative facing that’s separate from the wall that holds up the house. When the walls are framed with wood, as they are in most houses and townhouses, there is supposed to be an air gap behind the bricks to keep the moisture they absorb from wicking into the wall and causing it to rot. At the top of the facade, there is usually a cap of bricks angled away from the house. Above and below that cap should be metal flashing that extends up against the sheathing to help keep moisture from getting into the main wall.

So, assuming the bricks were installed correctly, the spalling you’re seeing is probably just a cosmetic issue. If the bricks were installed incorrectly and moisture is getting into your house, however, you should have a home inspector or an experienced contractor help you assess the situation.

Fortunately, most spalling on brick facades is just a cosmetic issue, said Edwuin Ayala, owner of Ayala Masonry in Fairfax, Virginia, which is often called in to repair brick walls similar to yours.

To keep more pieces from falling out, try to figure out why moisture is soaking into the bricks, and correct the underlying problem. The picture you sent shows a small pile of snow next to the base of the wall. If deeper piles of snow form there after a storm, shoveling the snow away will help keep the bricks dry and intact. If a gutter leaks overhead, plug the joint. If the yard slopes toward the wall, reslope the ground or install a drain system to keep water away.

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Ayala also recommends spraying the bricks with a waterproofing sealer every few years, a strategy that the Brick Industry Association also supports, provided other adjustments — such as the air gap, proper flashing and sloping of the yard — are done first. Waterproofing sprays can’t seal gaps in mortar joints and shouldn’t be depended on as the main line of defense in keeping a brick wall dry, the association says in another of its technical notes, “Colorless Coatings for Brick Masonry.”

If you want to replace the damaged bricks, that’s certainly possible. But line up the replacement pieces before you or anyone you hire starts taking out the broken ones. It might take some sleuthing to find bricks that match the color and size. A mason who frequently does repairs may be able to help.

The challenge is removing the damaged bricks without also damaging adjoining bricks. Ayala first drills through the mortar joints, spacing holes fairly close together, side by side, along each edge of the damaged brick. Then, using a cold chisel and a hammer, he knocks out the mortar until he frees enough space to wiggle out the damaged brick. It’s often not possible to remove just a single brick, because the hammering also loosens one or more neighboring bricks, which must then be removed. Typically, Ayala said, he has to take out two or three bricks for every damaged one. Once all the bricks that need to be taken out are off the wall, he removes all the loose mortar, mixes up a fresh batch and resets the intact bricks and the replacement pieces.

A handy homeowner can do the work, but this is the sort of repair that many people prefer to turn over to a professional. Ayala’s minimum fee, $500, covers a day’s work. He can often repair a facade in one day, but it depends on how many damaged bricks there are.