Water is the number-one enemy of a masonry chimney, and waterproofing is one of the most cost-effective ways to protect it. But it has to be done right — with the correct breathable sealant — to help rather than harm.
Why water is so damaging
Brick and mortar are porous, so they absorb rain. In our climate, that absorbed water freezes and expands every winter, breaking the masonry apart a little more each year. This freeze-thaw cycle causes spalling brick, failing mortar, and eventually structural damage.
What waterproofing does
A quality chimney waterproofing treatment is a breathable, water-repellent sealant applied to the exterior masonry. It stops rain from soaking in while still allowing moisture already inside the masonry to escape — which is critical. It dramatically slows freeze-thaw damage and extends the life of the chimney.
Why breathability matters
Ordinary sealants that trap moisture inside the brick actually make things worse, causing the masonry to deteriorate from within. Chimney waterproofing uses a vapor-permeable product designed specifically for masonry, which is why it should be done with the right materials.
When it is worth it
- Your chimney has sound but porous, aging brick
- You have addressed the crown, cap, and any failing mortar first
- You want to extend the life of a repointed or repaired chimney
- You are seeing early signs of water absorption or minor spalling
Protect your chimney from water damage
Careful work, up-front pricing, seven days a week in La Grange and the western suburbs.
Call (708) 432-5330Frequently asked questions
Is chimney waterproofing worth the cost?
For sound, porous masonry it usually is. It slows the freeze-thaw damage that causes most chimney deterioration, extending the chimney life for a modest cost.
Can I use regular sealant on my chimney?
No — ordinary sealants can trap moisture inside the brick and cause worse damage. Chimney waterproofing uses a breathable, vapor-permeable product.
Should I waterproof before or after repairs?
After. Address the crown, cap, and any failed mortar first, then waterproof sound masonry to protect it going forward.
How long does chimney waterproofing last?
A quality breathable treatment typically lasts several years before it needs reapplication, depending on exposure and the product used.
Written by Adam Evans, owner of Chimney Sweep Brothers and a chimney technician with 12 years of experience serving La Grange, IL and the western suburbs.