Chimney Waterproofing That Lets the Brick Breathe

A brick chimney stands above the roofline with nothing to shelter it, and New Jersey gives it plenty of water to drink. NOAA's 1991 to 2020 normals put Toms River at about 52 inches of precipitation a year and about 116 nights at or below freezing. Up in Newton the count of freezing nights climbs past 140. Water that soaks into a brick on a wet afternoon can freeze that night, expand, and push the face of the brick off a little at a time.

A good repellent slows that down. It is not paint and it is not a shiny sealer. It is a penetrating, breathable product made for masonry: it lines the pores so liquid water beads up, but water vapor coming out of the chimney can still escape. We only apply it to a stack that is already sound, because no coating can bridge an open joint or a cracked crown.

Signs you need this

• Brick that stays dark long after the rain stops
• White powdery bloom on the outside of the stack
• Brick faces flaking or popping off
• A damp patch on the chimney wall inside the house
• Moss or green staining on the shady side of the chimney

How we do it

1. Look at the whole stackAt the free inspection we check the crown, cap, flashing, mortar joints and brick faces, and take photos of anything that would let water in from the top.
2. Repair before coatingCracked crowns, open joints and loose flashing are fixed first and priced separately, so the repellent is not hiding a leak.
3. Prep and wait for dry brickLoose material, moss and soot staining come off, then we wait for the masonry to dry out, because repellent absorbs into dry brick and only skins over wet brick.
4. Saturate from the top downWorking top to bottom, we flood every face of the stack until it stops absorbing, and mask off shingles, siding and glass.

Why not seal the chimney with paint or a clear coat?

Film-forming coatings stop water vapor from leaving the brick. Water still gets in through the crown, a hairline crack or the inside of the flue, and once it is trapped behind a film it freezes and blows the face off from behind. That is how a sealed chimney can look fine for a year and then shed brick.

A breathable repellent works inside the pores instead of on top of them. After we leave, the chimney should look the way it did before, just without the dark wet patches after a storm.

Does a Shore chimney need it more than one inland?

Exposure matters more than the address. A tall stack on an open lot near the bay or ocean takes wind-driven rain and salt from more directions than a short stack tucked between trees in Morris County. Salt carried in that water crystallizes inside the brick as it dries, which is another way faces break apart.

Inland, the threat is the number of freeze and thaw swings. Sussex, Warren and inland Monmouth and Ocean all see well over a hundred freezing nights a year, and every one of them works on wet brick.

What moves the price inside the $300 to $800 range?

Height above the roof, roof pitch, the number of flues and how much prep the brick needs are the main factors. A short single-flue stack on a ranch is at the low end. A tall, wide chimney on a steep roof, or one that has to be reached from a ladder set on a porch roof, sits higher. Your price is written down at the free inspection before anything is done.