Masonry Chimney Damage & Repair

Damaged Masonry ChimneyRegular maintenance on your masonry chimney will keep it looking great for years. In reality, though, regular maintenance falls through the cracks while you juggle work, life and family. Sometimes, even the most proactive homeowners will be surprised by damage left by previous owners. So while in a perfect world, repointing would be the only masonry service the average masonry chimney would need, in reality you might find unfamiliar problems with your masonry.

Masonry Chimney Damage

Chimney with Spalled BrickSpalled Bricks

Broken (or spalled) bricks are one of the most noticeable types of damage. This is most commonly seen when the front of the brick has either broken or fallen from the masonry.

We’ve mentioned before that the largest cause of damage to brick and masonry is freeze and thaw cycles. Bricks are built to withstand water by finishing them with a hard non-porous outer shell. Spalled bricks break this shell and expose the porous interior of the brick, allowing water damage to destroy your masonry at an accelerated rate.

Spalled bricks are primarily caused when mortar with an incorrect compression rate is used. Mortar is made to absorb the expansion of brick during freeze and thaw cycles. If the mortar is stronger than the brick, however, this role reverses. As brick isn’t meant to be squeezed by expanding materials, it can quickly deteriorate.

The Wrong Bricks

All bricks are not created equal. Brick makers understand that interior bricks don’t need to weather the same abuse as exterior bricks, and thus make different types of bricks. When buying bricks, the difference between these is obvious. It becomes a problem, however, when bricks are salvaged. Inexperienced masons and do-it-yourselfers have a difficult time determining which bricks were meant for interior and exterior use.

Some brick makers even make different bricks for different climates. The Deep South is free from freeze and thaw cycles, so some brick makers decided to change the type of brick they shipped there. Since these bricks didn’t need to withstand the same type of abuse as bricks used in the North, they added sawdust to the brick mix. When the bricks were fired, the sawdust burnt away, creating a lighter, more porous brick. This saved on transportation and made it easier for masons. While this caused little problems for the South, unfortunately these bricks were soon being sold further north, where they easily crumble under the extreme temperatures.

Damage from sandblasters and pressure sprayers

An unexpected source of damage is sandblasters and high pressure sprayers. While these might make cleaning a hands free experience, they do so at the expense of your masonry. As mentioned earlier, brick is made such that the edges are hardened to prevent absorption of water. Sandblasting and even high pressure sprayers can reduce this hardened edge and allow water into your bricks, drastically reducing their lifespan.

Masonry Chimney Repair

Unfortunately, there’s no easy way to fix spalled bricks. Removal of the spalled bricks and replacement with strong new bricks is necessary. If the spalling is caused by poorly calculated mortar, repointing with correct mortar may help to prevent the problem from spreading.

If you suspect your masonry might be made with bricks that can’t stand up to your weather, or if you have sandblasted or pressure sprayed your masonry, we can apply a waterproof sealant to help the longevity of the bricks.

And of course, if you notice any spalled bricks, cracks, crumbling mortar, or signs of deterioration on your masonry chimney, it’s time to contact a masonry expert right away. Ignoring masonry problems is dangerous and costly.

If you have questions about masonry repair in Northern Virginia, Washington D.C. or Maryland, we at High’s Chimney would be happy to answer any of your questions or take a look at your masonry and give you an estimate for repairs free of charge.

2 thoughts on "Masonry Chimney Damage & Repair"

Andrew says:

Thanks for the great article. You seem really knowledgeable. Maybe you’d send me an email reply?

I have a white brick house (50 years old). The same brick type is used on all outer walls and the chimney. Just to give you an image, I’d say that the bricks look something like
The bricks are not perfectly smooth.

The problem is that I find that some bricks are delaminating. The front 1/4 inch is splitting off and falling to the ground. This is ONLY happening on the bricks on the chimney. All around the house the bricks are intact. I would say that 30 bricks have delaminated on the chimney and it is continuing to happen.

I am not excited about starting with masonry (digging out the broken bricks and replacing them) until I know why it is happening and can fix it.

In your opinion, is the problem most likely to be:
a) Cracks in the tile in the interior of the chimney. A chimney sweep saw a crack in the tile with his mirror, and thinks that the chimney should get a liner (if we want a working chimney) or an insert.
b) The pitch of the slate on the slanted part of the chimney. The chimney is wider at the bottom, goes up straight, and then there is a slanted part, covered with a big piece of slate. Sorry for not knowing the technical term.
When it rains, water spills off the front of this slate and dribbles down the front face of the chimney. Now, most but not all the delaminated bricks are below this slanted part, but a few are definitely above it. So this can’t be the whole reason.
c) Possible problems with flashings, gutters, or other issues that may have been good for roof water runoff but not right for dealing with the chimney. We have a terra cotta tile roof, in case that’s relevant.
d) The issue of this article. Could the type of mortar be too unforgiving with incorrect compression rate, and is this somehow a much bigger problem on a chimney than on the rest of the home? How could I determine whether this is the problem, before just jumping in and repointing the whole chimney?

I hope you can find a minute to answer my question. I have had many masons out to the house, and no one seems to know why we have chimney-only delimitation. Of course we didn’t supervise construction of the house, so we don’t know how it was originally built.

Any insights very welcome.
Thanks again!

Jonas Braud says:

Could the brick deterioration be caused by efflorescence in your brick chimney? I reviewed this page as I prepare to clean and seal my chimney before I have a new roof installed.

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