Chimney Leaks & Waterproofing
A chimney is the only part of your roof with a hole deliberately left in the top of it. When water gets in, finding the actual entry point is most of the job.
We diagnose before we sell you a sealer. Half the leaks we see are not porosity.
Common entry points
- Missing, undersized or damaged cap
- Cracked or flat crown with no overhang
- Failed or surface-mounted flashing
- Open mortar joints and porous brick
- Rusted-through chase cover on a framed chase
- Condensation inside an oversized flue
The stain on your ceiling is not where the water got in
Water entering at the crown can travel a long way inside a masonry chimney before it shows itself, and it almost never appears directly below the failure. This is why so many chimney leaks get chased for years with the wrong repair. We work from the top down and rule things out in order rather than guessing at the cheapest fix first.
Symptoms inside
- Brown staining on the ceiling or wall beside the chimney breast
- Peeling paint or bubbling plaster near the fireplace
- A damp, musty or heavily sooty smell after rain
- Visible water or dripping in the firebox
- Rusted damper or rust staining down the firebox wall
- Efflorescence, the white powdery salt bloom, on interior masonry
Symptoms outside
- Dark, persistently damp patches on the stack after rain has stopped
- White staining on the exterior brick
- Cracked crown, or a crown poured flat with no slope
- Rusted cap, or no cap at all
- Flashing lifting, or sealed only with roof cement
- Moss or vegetation growing in the joints
Where the water is actually coming from
No cap, or the wrong cap
The most common and the cheapest to solve. An open flue takes rain straight down onto the smoke shelf and damper. See caps and crowns.
A failed crown
The crown is the concrete slab across the top of the stack. It should slope away from the flue and overhang the brick with a drip edge. Most of what we find is a thin flat mortar wash, cracked through.
Flashing
The metal junction between chimney and roof. Done properly it is stepped and cut into the mortar joints. Done badly it is a bead of black roof cement that has hardened and split.
Porous masonry
Brick and mortar absorb water directly. On an exposed elevation with driving rain this alone is enough to wet the interior of the stack.
Open mortar joints
Once joints have opened, water does not need to be absorbed. It runs straight in. This is a masonry repair, not a waterproofing job.
Condensation
Not a leak at all, but it looks like one. An oversized or uninsulated flue lets flue gas cool and condense on the walls, which then runs back down. The fix is usually relining.
The right product, applied at the right time
Waterproofing masonry is genuinely effective, but only once the structural entry points are closed. Sealing a chimney that has open joints or a cracked crown traps the water already inside it and accelerates the damage. We will not sell you a sealer application on a chimney that needs pointing first.
Diagnose the leak
Roof-level inspection of cap, crown, flashing and joints, plus an interior look at the firebox and damper for the signature of where water has been running.
Fix the entry points
Cap fitted or replaced, crown repaired or rebuilt, flashing cut in and sealed, joints repointed. Whatever the diagnosis actually calls for.
Let the masonry dry
Sealing wet brick locks the water in. Where the stack is saturated we come back rather than push on.
Apply the sealer
Full saturation application to the exposed masonry, worked from the bottom up so the surface stays wet and the product penetrates rather than skinning over.
Check the result
You should see water bead and run off the brick rather than darken it. That is the test, and it is one you can do yourself with a hose next spring.
Leaks and waterproofing, answered
My roofer says it is the chimney and my chimney company says it is the roof.
This is the most common standoff in the trade, and the honest answer is that the flashing sits between the two. We work on flashing, we photograph what we find, and we will tell you plainly if the problem is the roof surface rather than the chimney. You are entitled to a straight answer, not a handoff.
How long does waterproofing last?
A quality siloxane application on sound masonry typically performs for several years before it wants renewing. Exposure matters. A south-west facing stack taking driving rain works harder than a sheltered one.
Can I use a general masonry sealer from the hardware store?
Check whether it is vapour permeable. If the label talks about forming a film or a coating, it is the wrong product for a chimney. The failure is slow and the damage shows up as spalled brick a few winters later.
Is a leaking chimney urgent?
More than most people assume. Water is what destroys chimneys, and it also rusts dampers, damages fireboxes, rots framing behind the masonry and can reach the ceiling below. It rarely stays a cosmetic problem.
Do you fix the ceiling damage too?
We fix the cause and stop the water. Interior finish repair is a separate trade, and we will happily tell you when it is safe to have that work done.
Everything else we handle on the chimney
Most of our visits turn up more than one thing. Because we do the cleaning, the masonry, the liner work and the waterproofing ourselves, you are never handed off to a second contractor.
Serving Chester County and the surrounding townships
We work out of Chester County and cover the boroughs, townships and rural stretches around it. Pick your town for local detail, or call and we will tell you straight away whether you are on our route.
Stop the leak at the source
Full leak diagnosis, cap and crown work, flashing and breathable waterproofing across Chester County.