Masonry waterproofing and sealing
Sealing a brick wall extends the life of the repair underneath it. Sealing a wall that still needs repair traps the water inside and makes everything worse. The order matters more than the product.
What sealing does and does not do
A masonry sealer is a breathable water repellent. It sits in the surface of the brick and stone and stops liquid water soaking in, while still letting vapour out. What it does well is reduce how much water a sound wall absorbs during driving rain, which means less freeze damage and a longer life for the mortar joints.
What it does not do is bridge a gap, fill a crack, or hold a failed joint together. It is a finishing coat on a repair, not a repair.
Why order of operations is the whole job
Here is the failure mode we get called out to. A wall has open joints and is letting water in. Someone seals the outside face. The sealer does not close the open joints — water still gets in through them — but it does slow the wall's ability to dry back out through the face.
Now the water going in has a harder time coming out. It sits in the wall through the winter, freezes, and the brick starts spalling on a wall that had only needed pointing. We have seen handsome sealing jobs on walls that were being destroyed underneath them.
So: point it first, replace whatever brick has already gone, and then seal. In that order it is genuinely worth doing.
When it is worth it
- Immediately after a full repointing, to protect the work you just paid for
- On elevations that take the prevailing weather and stay wet longest
- On soft, porous older brick that drinks heavily during long rain
- On chimneys and parapets, where exposure is worst
And when it is not worth it: on a wall with open joints, on a wall with active spalling, or as an answer to an interior damp problem whose source has not been identified yet.
Coatings that seal the wall shut
Be careful with heavy film-forming paints and waterproof coatings sold for masonry. Unlike a breathable repellent, these can seal the face of the wall completely — and a wall that cannot breathe out is a wall holding its water in.
On old Chicago brick that usually ends badly. If a previous owner has already coated your brick, tell us, because it changes what the wall needs and it changes what we can sensibly do to it.
Get a waterproofing price
Estimates are free and there is no obligation attached to one. Tell us what you are seeing and we will tell you what it actually needs.