Chimney services, Portland metro
Chimney waterproofing with a breathable repellent, after the masonry is sound
We treat the chimney brick above your roof with a breathable siloxane-type repellent that lets masonry dry out while keeping Portland rain from soaking in. It goes on in a dry window after the joints and crown are repaired, never instead of that work.
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What you are seeing
Homeowners often call about waterproofing after a wet winter or two leaves these marks on the chimney.
- Brick that stays dark and damp for days after the rain stops, while the rest of the wall dries.
- White, powdery streaks on the outside of the chimney, heaviest just below the crown.
- Moss or black algae on the north or shaded face of the stack.
- Thin flakes of brick face in the gutter or on the roof under the chimney.
- A wet, earthy smell from the fireplace after a storm, even with the damper shut.
- A repointing or crown job done recently that you would like to protect.
What we do on a waterproofing visit
Waterproofing is the last step in a sequence, so the visit starts with the parts that have to be right before any repellent goes on.
Walk the stack and find where water is already getting in
Before anything is sprayed we go up and look at the crown, the cap, the flashing and every joint on the weather face, and we photograph what we find. A repellent slows rain soaking into the brick; it has no effect on a crack in the crown or a gap in the flashing. Those get fixed first or the treatment is money spent on the wrong problem.
Clean off the moss, algae and efflorescence
Moss holds water against the brick and the shaded side stays wet longest, so the growth is scraped and brushed off and the face washed at low pressure. White efflorescence is brushed off dry. High-pressure washing drives water deep into old lime mortar, so the pressure washer stays on the truck.
Repoint and repair the crown before the repellent
Open joints are ground out and repointed, and a sound crown with hairline cracks gets a flexible crown coat, on an earlier visit when the work is more than a patch. The repellent goes on after that mortar has cured. Waterproofing over soft, washed-out joints seals nothing; the water simply enters at the joint instead of the brick face.
Mask the roof and apply the repellent from the bottom up
Plastic goes over the shingles and the flashing below the work, because some repellents mark metal and roofing. We spray a breathable siloxane-type product with a low-pressure sprayer, starting at the roofline and working up so each pass floods the one below, then put on a second coat while the first is still wet. Overspray is wiped off the cap and the crown.
Check that the brick still breathes and now sheds
Once the surface has flashed off, water dripped on the treated brick should bead and roll rather than darken the face, while water vapor from inside the flue can still escape outward. That is the difference between a repellent and a sealer. We also confirm the cap is tight and the crown overhang is dripping clear of the brick.
Photograph the finished stack and note the product and date
You get the before and after photos, the name of the product, the date it went on and the weather it went on in, so whoever looks at the chimney in a few years knows what was done. We write down anything we saw that waterproofing will not reach, such as flashing at the end of its life.
Breathable repellent or film-forming sealer: why the choice matters here
A breathable repellent is the right choice on brick: it soaks into the pores and sheds liquid water while letting vapor out, and a film-forming sealer traps whatever moisture is already inside the masonry.
Trapped moisture is the problem, not the cure. When it freezes it pops the face off the brick, which is the spalling you see on chimneys that were painted or coated years ago. Portland sees roughly 32 nights a year at or below freezing, nearly all of them in the five wettest months, so the brick is often wet when it freezes.
Siloxane and silane products are the breathable family. They penetrate rather than coat, they leave the brick looking the same when dry, and they can be reapplied without stripping anything. That is what goes on clay brick.
Why the repointing and the crown come first
Repointing and the crown come first because water gets into a Portland chimney mainly through the open joint, the cracked crown, the missing cap or the lifted flashing, not the face of a sound brick.
The trade calls those the four usual entry points, and a repellent addresses none of them. So the order is fixed: joints repointed, crown coated or poured, cap on, flashing tight, then the repellent across everything as the last layer.
When we find more than a patch of repair, we quote it as its own job and schedule the waterproofing after the mortar has cured, usually a few weeks later in a dry spell.
When a Portland chimney can be waterproofed
July and August, and the dry weeks on either side of them, are the window. The airport records about 157 days a year with measurable rain, and roughly 65 percent of the yearly total falls between November and March.
The brick needs to be dry through its thickness, not just on the surface, which after a wet spring can take days of warm weather. Then the product needs to cure before the next rain, and the roof needs to be dry enough to stand on.
That is why we book waterproofing for summer and keep a short list of chimneys to treat when a dry stretch opens in May, September or early October. A repellent sprayed onto damp brick in November cannot soak in properly and fails early.
What moves the price of chimney waterproofing
The posted figure covers a single-flue chimney reachable from the roof, and these are the things that take it higher.
- Chimney size: a wide two-flue stack or a tall stack on a steep roof takes more product and more time on the ladder.
- Scaffolding or a lift, when the chimney cannot be reached from the roof or the pitch is too steep to stand on.
- Heavy moss or years of efflorescence that need a full cleaning visit before the treatment.
- Repointing, crown work or flashing found during the walk-around and done ahead of the repellent.
- A third coat on soft, porous old brick that drinks the first two faster than modern brick does.
What a water repellent leaves for other repairs
A repellent keeps rain out of the brick face and the mortar surface; everything else that leaks is a separate fix, and we tell you which one.
Water in the firebox after a storm often comes straight down an uncapped flue, which is a cap. A stain on the ceiling beside the chimney breast often means flashing. A crown with a crack you can see from the ground needs a crown coat or a new pour before any spray.
When a repair stops making sense
Waterproofing stops making sense when the brick is failing. If faces have spalled off across much of the stack, or the mortar washes out in your hand, a repellent only delays the day the chimney above the roof is taken down and relaid.
The same goes for a crown that is broken into pieces rather than cracked. It gets poured new, with an overhang and a drip edge, and the repellent goes on afterward as a finish rather than a fix.
Waterproofing: common questions
Will chimney waterproofing stop the leak that is already staining my ceiling?
Usually not on its own: a stain that reaches the ceiling is most likely coming through the flashing, the crown or an open joint. A repellent treats the brick face. We find the entry point first, fix it, and then waterproof the stack so the brick stops holding water through the winter.
How long does chimney waterproofing last in Portland weather?
A breathable repellent wears off gradually rather than all at once, and it goes first on the face that takes the wind-driven rain. The easy test is to drip water on the brick on a dry day: when it soaks in and darkens instead of beading, it is time to reapply. We record the product and date so you can plan it.
Can you waterproof a chimney that has moss growing on it?
Yes, after the moss is off and the brick has dried, because a repellent sprayed over moss seals the moss to the wall and nothing else. We scrape and brush the growth off, wash the face at low pressure, and come back for the treatment once the stack has had a few dry days.
Does chimney waterproofing change the color of the brick?
No, a siloxane-type repellent dries clear and leaves the brick looking as it did when dry. That is the point of a penetrating product instead of a glossy film. The one visible change is in the rain: treated brick stays its dry color while the untreated wall beside it darkens.
Is chimney waterproofing worth doing right after a tuckpointing job?
It is the right time to do it, once the new mortar has cured. Fresh joints and old brick are both porous, and the repellent keeps rain from soaking into either, so the repointing lasts longer before the next freeze finds a joint. We often quote the two together with the waterproofing a few weeks after.
What month should a Portland chimney be waterproofed?
July or August, when the brick has dried through and the product can cure before rain returns. A warm dry stretch in late spring or early fall works too. We keep a list for those windows, and a chimney that comes up in November is scheduled for the next dry season rather than sprayed wet.
Related pages
Where we do this
Waterproofing is a summer job across every area below, and we group the dry-week bookings by neighborhood so one trip covers several roofs.
Ready to book a sweep?
Call with what the fireplace is doing, or text a photo of the opening and one of the chimney top, and we will name the service and its posted price before we come out.