Don’t overlook a flaking concrete cavity block when surveying your home for damage. Most often, these blocks, with a hollow center containing two to three holes, are the construction mainstay of basement walls, home foundations and block fencing.

Extreme temperature shifts and moisture damage can wreak havoc on the concrete. So what should you do when faced with a block or two that’s in need of replacement in an otherwise sound structure?

Depending on the damage, you’ll most likely only need to replace part of the block, usually the face and middle support. With a bag of prepackaged mortar—available at home improvement stores—and some masonry tools, you can repair the damage easily. Just add water to your mortar mix and follow these instructions.