A board asked me to repaint a wall covered in paint blisters — what was inside them told me the repaint would have failed too
A property manager walked me along the south wall of her mid-rise last summer, pointing at paint blisters the size of loonies, and asked for a repaint price. Before pricing anything I did what I always do: cut a few blisters open. What’s inside a blister — water, air, or bare substrate — tells you exactly why it formed, and each cause needs a different fix. This post is for property managers and condo boards looking at blistered exterior paint and wondering whether a repaint will actually hold.
1. Cut the blister open before you blame the paint
A blister is the paint film letting go of whatever is under it and inflating. The film itself is usually fine — the failure is at the bond line. That’s why “better paint next time” is almost never the answer on its own.
I open a few blisters with a knife and look at two things: what’s inside the dome, and what’s on the back of the peeled film. Wet interior or water droplets mean moisture is being pushed out through the wall. A dry dome with chalky residue on the back of the film means the last coat went over a surface that was never sound. Bare, shiny substrate means the whole coating system — not just the top coat — has let go.
What to look at: pick three blisters on the worst wall and open them. Note wet or dry, and whether the film pulled paint or pulled clean.
2. Water-filled blisters are a wall problem, not a paint problem
When blisters carry water, the wall is taking on moisture from somewhere — failed caulking at windows and joints, open coping at the parapet, a grade-level splash zone, or vapour drive from inside the building pushing outward on sun-heated walls. The sun heats the wall, the moisture turns to vapour, and the vapour inflates the weakest spot in the film.
Repainting over this fails on a predictable schedule: it looks good for a season, then the same walls blister again — usually the south and west exposures first, because they take the most heat. The money has to go to the water source first. On most buildings that’s a caulking and sealant repair, which costs a fraction of chasing repaints every two years.
What to look at: map where the blisters are. If they cluster on sun-exposed walls, below joints, or around penetrations, you have a moisture path — find it before anyone opens a paint can.
3. Dry blisters usually mean the last crew painted in the wrong conditions
Dry, air-filled blisters most often form on the day of application: paint applied on a hot surface in direct sun skins over before the solvents underneath escape, and the trapped solvent inflates the film. On commercial repaints I see this on walls that were painted in the afternoon sun in July. The blisters can show up within days.
The other dry-blister cause is painting over chalk or dust. Exterior paint that has weathered past its service life breaks down into a powder — you can wipe a dark rag across the wall and see it. New paint bonds to the powder, not the wall, and the bond fails in sheets of small blisters. Proper prep here is a wash-down and a binding primer, and it’s the difference between a 10-year repaint and a 3-year one.
What to look at: ask your last painter’s records for application dates and weather. If the blistered walls were done in mid-summer afternoon sun, conditions are your likely cause.
4. The repaint spec follows the diagnosis — not the other way around
Once I know the cause, the scope writes itself. Moisture blisters: seal the water path, let the wall dry, spot-prime, then repaint. Solvent blisters: scrape and sand back to sound film, repaint in the right conditions — early morning or shaded rotation on hot days. Chalk-bond failures: full wash, binding primer, two coats. On a mid-rise, the difference between these scopes can be tens of thousands of dollars, which is why a blister diagnosis belongs in the quote stage, not after the failure.
Most blistering I see in Ottawa is preventable. Almost none of it is about the paint being cheap.
What to look at: any repaint quote for a blistered wall should name the cause and the prep. If it only names the paint brand and colour, the diagnosis step got skipped.
What to do if you’re seeing any of this
If your building has blistering paint, don’t start with a repaint price — start with ten minutes and a knife. Or have someone like me do it: I assess blistered and failing exterior coatings on condo and multifamily buildings across Ottawa, Kanata, Nepean, Orleans, Barrhaven and Stittsville, and the assessment tells the board what the repaint has to include for it to last. Call 613.325.3011 or email yasir@heims.ca and I’ll walk the wall with you.
— Yasir, HEIMS Construction
HEIMS Construction is an Ottawa-based commercial painting and drywall contractor serving condominium corporations, property managers and institutional clients across the Ottawa area. We are licensed and insured, and members of BOMA Ottawa.