How to Repair a Brick & Mortar Chimney
Chimneys are as exposed to the elements as any other exterior portion of a house, and in some cases, more so. As a result, the brick and mortar of a chimney often needs repair before the rest of the exterior masonry. The procedure for replacing cracked bricks and repointing mortar is similar to what you might do for the rest of the house, but it must be undertaken with greater care as the top of the chimney is essentially a small, freestanding structure. Does this Spark an idea?
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Things You'll Need
- Hammer
- Cold chisel
- Wire brush
- Marker
- Tape measure
- Ruler
- Brick set
- Trowel
- Mortar bag
Instructions
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1
Chip out cracked or crumbling mortar and the mortar around any cracked or chipped bricks in need of replacement by striking it with a hammer and a cold chisel. Keep chipping away at the mortar until you have removed all of it in a given joint.
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2
Scrape out mortar debris remaining in the chimney's joints with a wire brush.
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3
Prepare replacement bricks that need to be shortened to fit an existing space. Measure the existing brick with a tape measure and use a marker and ruler to draw a straight cutting line around a new brick.
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4
Cut a groove into a replacement brick by placing the cold chisel against the marked line at a 60-degree angle and tapping it with the hammer. Switch from left to right, keeping the 60-degree angle, to ensure a smooth groove. Then place a brick set (a sharp-edged chisel) into the groove and strike it hard with the hammer, splitting the brick along the cutting line. Repeat for any additional replacement bricks.
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5
Use a trowel to spread a layer of mortar into the bed of the space requiring a replacement brick (usually the top of the bricks underneath), matching the thickness of the existing joints in the chimney.
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6
Butter the ends and the top of the replacement brick with mortar, using the trowel. Try to match the thickness of the existing joints; favor putting too much mortar on the brick over too little.
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7
Push the brick into the space in the chimney wall, and scrape off excess mortar with the trowel. Shape the wet mortar in the joints with the trowel to match the existing joints. Repeat Steps 5 through 7 for all replacement bricks.
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8
Pour mortar into a mortar bag. Squeeze the mortar through the bag's nozzle and into the remaining empty joints (left by removed cracked and/or crumbling mortar not connected to a damaged brick). Shape this mortar to match the surrounding joints with the trowel, as in Step 7.
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Tips & Warnings
Many houses built before the mid-20th century were constructed using old fashioned lime and sand mortar, rather than the Portland cement-based mortar in common use today. Modern mortar mixes are much harder, as are the bricks that go with them. Combining modern mortar mix and old bricks often results in the hard mortar cracking the old brick -- so make sure you know what kind of mortar was used on your chimney before you repair it.
Always start this task by assessing how much mortar and brick needs to be removed, and whether this can be done safely in one big push. Remember that removing bricks and mortar from a masonry structure weakens it. Pulling several bricks all at once from the same area might cause the entire chimney to collapse, so err on the side of caution -- even if it means pursuing a repair job in stages.
References
- Photo Credit Jupiterimages/Photos.com/Getty Images
