CONSTRUCTION : Repointing Mortar Joint Takes Some Care

Even well-made mortar joints between bricks can suffer damage over time, especially when they are exposed to severe weather.

Cracked or crumbling joints allow moisture to penetrate the wall, where it can freeze and cause even more extensive damage. Inspect exterior masonry every few years--before cold weather makes masonry work impractical--and repair damaged joints as soon as possible.

Fixing mortar joints is called repointing (or tuck-pointing). It involves chiseling out damaged mortar and replacing it. Although the process is not difficult, you should evaluate the job carefully. It’s easy to repair small areas, even on a chimney, if they are near the ground.

But if your task requires scaffolding or major rebuilding of brick facing, call a professional mason. Similarly, if your chimney lacks a liner or has holes, large gaps, or smoke coming from anywhere but the top, call a mason.

You will need a small sledgehammer, a cold chisel and an old paint scraper to remove the old mortar. You’ll also need a stiff-bristled wire brush, a trowel, and a tuck pointer (a trowel with a long, narrow blade) to work the mortar into the joints, and a brick jointer, a tool that gives a mortar joint its final shape. All are available at hardware stores and home centers, which also sell the ready-mix mortar you’ll need.

Be sure to wear safety goggles when chiseling and cleaning joints. In addition to goggles, wear protective clothing, including gloves, when working with mortar. Mortar is mildly caustic. If it splashes on your skin, wash it off with water.

Tap Out Loose Mortar

Use a chisel and sledge to tap out loose mortar in each joint to a depth of at least one inch or until you reach solid mortar. Hold the chisel at a sharp angle and try not to chip the bricks. Rake the joints clean, leaving a flat surface at the back of the cut. Brush the joints vigorously with the wire brush.

Pour some ready-mix mortar into a bucket, add a little water gradually until the mix is a uniform stiff paste that you can change into a ball. Let it stand for 10 minutes and stir again before using.

Work on the bricks from the bottom up. Start by brushing water into the joints. This prevents the mortar from being weakened by losing its moisture to dry bricks. Scoop some mortar onto a trowel, hold the trowel up to the joint, and push the mortar in with the tuck pointer. Fill vertical joints first, then horizontals. Fill deep joints in layers; allow each layer to stiffen somewhat before applying the next one. After filling each joint, smooth the mortar with the tuck pointer.

New mortar should match the old as closely as possible in composition, color and joint profile. To check the color, mix a small batch of mortar, repoint an inconspicuous area and let it dry (it will lighten in the process).