Chimney Repointing and Spalled Brick Repair in Denver

Denver has about 156 nights a year at or below freezing, according to NOAA's 1991 to 2020 normals, and most of them are followed by a thaw. Colorado sun warms a south-facing chimney quickly in the afternoon, and the night freezes it again. Water that soaked into the joints expands each time it freezes. Over the years the mortar turns to sand, and the faces of the bricks flake off, which masons call spalling.

Repointing means grinding out the failed mortar and packing new mortar into the joints. On older Denver brick, which is often softer than modern brick, the new mortar has to be weaker than the brick. A hard modern mix on soft old brick makes the brick crack instead of the joint. Plan on $500 to $1,200 for spot work and $1,200 to $2,500 to repoint everything above the roofline.

Signs you need this

• Sand-like mortar in the gutter or on the shingles
• Joints sunk well behind the brick face
• Brick faces flaked off, showing rough inner brick
• White powdery staining on the brick
• Loose bricks at the corners of the stack

How we do it

1. Map the jointsWe check every face of the chimney and mark which joints have failed and which bricks are spalled.
2. Cut out old mortarFailed mortar comes out to an even depth, by grinder and hand tools, without chipping the brick edges.
3. Repack the jointsMortar matched to the brick's strength and color goes in, in layers, and is tooled to shed water.
4. Replace spalled brickSpalled units come out whole and the nearest match goes in. Bigger areas typically run $1,000 to $3,500.

Is the white staining on my chimney a problem?

The white powder is efflorescence, salts left behind when water moves through brick and mortar and dries on the surface. The salt itself is harmless and brushes off. What it tells you is that water is getting into the chimney, from a crown, a cap, open joints or the flashing.

If the staining keeps coming back, we look for where the water enters before doing any repointing, because new mortar will not last if water keeps soaking the stack.

Can I just seal the flaking brick myself?

We do not recommend it. A sealer that forms a film traps moisture inside the brick, and in a climate with about 135 freeze-thaw days a year that trapped water freezes and pops the faces off faster. Painting over spalled brick has the same problem.

The order that works is repair first, then a breathable water repellent that lets vapor out but keeps rain from soaking in. That repellent typically costs $300 to $800 for a chimney, after the masonry is sound.

Repoint or rebuild?

Worn joints around solid brick call for repointing. If bricks are loose, cracked through or the stack leans, new mortar will not hold it together, and rebuilding the top courses is the honest answer. We tell you which it is with photos.