Painting is the most-attempted DIY project in Ottawa. Most homeowners take it on at least once. Most homeowners also call us six to nine months later because the trim is peeling, the corners are cracked, or the new coat is bleeding the old yellow ceiling stain through.
Painting is forgiving in the moment. The roller goes on smooth, the colour looks right, the room reads clean. The problems show up between month four and month nine, when the prep shortcuts catch up. Below are the seven prep mistakes I see most often on DIY paint jobs in Ottawa, and what to do instead.
1. Skipping the wash
Walls in a kitchen, bathroom, or hallway carry a thin film of cooking grease, hand oil, hairspray residue, dust, and (in homes with smokers) nicotine tar. Paint does not bond to that film. It bonds to the layer of new paint applied on top of the film, which is itself only bonded to the film, which is bonded to nothing.
Six months in, the new paint starts releasing in sheets when something rubs against it. Light switches develop halos of peeling paint. Trim near doorways flakes around handles.
The fix is one bucket of TSP (trisodium phosphate) substitute or a degreaser like Krud Kutter. Mix per the label. Wipe walls top to bottom with a sponge or microfiber. Let dry 4 hours. Skip this step on bathrooms, kitchens, hallways, and any room above a heat register and the paint will fail.
2. Painting over old caulk
The corner where wall meets ceiling, or where wall meets trim, is usually caulked. Old caulk shrinks, cracks, or pulls away from the surface over time. Painting fresh paint over a cracked caulk line locks the crack into the new finish: it shows as a hairline scar that gets worse every season as the house expands and contracts.
The fix:
- Inspect every caulked seam at eye level and at chair-rail level.
- Where the caulk has cracked, separated, or pulled away, cut it out with a utility knife or a caulk-removal tool.
- Clean the joint with a damp cloth. Let dry.
- Apply a fresh bead of high-quality paintable acrylic latex caulk (DAP Alex Plus or Sherwin-Williams 950A). Smooth with a wet finger or a caulk-finishing tool.
- Wait 24 hours before painting over fresh caulk. Many DIYers paint within 4 hours and the caulk does not skin properly, leading to the same crack returning within months.
3. Skipping primer on patches and stains
Drywall patches (where you filled a nail hole or a doorknob dent), water stains, smoke stains, marker stains, oil-based old paint: each one needs a stain-blocking primer before topcoating. Latex paint does not seal stains. It floats on top of them, and the stain re-emerges in 4 to 12 weeks.
The right primers for the right jobs:
- Drywall patch primer: Zinsser Bulls Eye 1-2-3 or Sherwin-Williams ProBlock. Latex-based, sands smooth, accepts topcoat in 1 hour.
- Water stain blocker: Zinsser Cover Stain (oil-based) or Zinsser BIN (shellac-based). Standard latex primer will not stop a water stain.
- Smoke and grease stain blocker: Zinsser BIN. Shellac primers are the only thing that reliably blocks deep stains.
- Bonding primer for slick surfaces (oil paint, PVC trim, polished tile): Stix or XIM-UMA. Required when painting over old gloss or semi-gloss finishes.
The DIY shortcut: skipping primer because "the paint says self-priming." Self-priming paint is fine on a previously-painted clean surface. It is not a substitute for a stain-blocker on a stained or patched surface.
The water stain test
If you have a water stain on a ceiling, touch it. Sniff your finger. If there is any musty odour, you have a moisture problem that has not been resolved. Painting over an active leak is a guaranteed re-failure. Find the leak source first, fix it, let the area dry for 2 to 3 weeks, then prime with shellac and paint. Many ceiling stain "fixes" we get called about are leaks the homeowner painted over twice without solving the source.
4. Sanding inadequately or not at all
Glossy and semi-gloss surfaces (most trim, most kitchen and bathroom walls in older Ottawa homes, most cabinet doors) need to be deglossed before fresh paint goes on. Either light sanding with 220-grit until the sheen is uniformly dull, or a chemical de-glosser like Krud Kutter Gloss-Off, or a bonding primer.
What goes wrong without sanding: the new paint sits on the gloss, looks fine for a few months, then starts releasing as soon as anything touches it. Trim peels off in strips, often pulling adjacent paint with it.
The right approach:
- Wipe the surface clean (TSP wash from step 1).
- Sand with 220-grit on a sanding sponge, working over every surface to remove the sheen. Light scuff, not deep cut.
- Vacuum the dust, then wipe with a tack cloth or a damp microfiber.
- Prime with bonding primer on any surface that was previously oil-based.
- Topcoat.
For kitchen cabinet repaints especially, sanding is non-negotiable. Cabinet failures from skipped sanding are the single most common DIY paint callback.
5. Painting in the wrong humidity
Latex paint cures by water evaporation. Oil-based paint cures by oxidation. Both processes need a specific humidity range to work properly.
The right conditions:
- Temperature: 10 to 27 degrees Celsius (50 to 80 F). Paint applied below 10 C does not coalesce properly and looks chalky.
- Humidity: 40 to 70 percent relative humidity. Above 80 percent, latex paint takes too long to dry and develops surfactant leaching (sticky water-soluble streaks).
- Surface temperature: 10 C above the dew point. Cold walls in winter (especially exterior walls in older Ottawa homes) can be 8 to 12 C colder than the room air; paint cures poorly on a cold surface.
Ottawa-specific issue: painting in February when the indoor humidity is 18 percent and the air is 22 C looks fine, but the paint dries too fast and lap marks become permanent. Painting in July with the windows open at 80 percent humidity and 28 C looks fine and does not cure for 14 days, attracting dust and bugs.
The honest answer for Ottawa: April, May, September, October are the best months. Indoor temperature 20 to 24 C, run a humidifier or dehumidifier to land in the 50 to 60 percent range, and you have ideal conditions.
6. Bad masking and edge work
Paint lines fail at the edges first. Three common edge mistakes:
- Cheap painter's tape that bleeds. Generic blue tape is 1.4 to 1.8 mil thick and bleeds at the edge. FrogTape (delicate green) and 3M Edge-Lock are 2.4 to 3.0 mil and seal cleanly.
- Tape applied to dirty surfaces. Tape needs a clean, dry surface to seal. Dust under the tape edge is where the bleed starts.
- Pulling tape too late. Tape pulled when the paint is fully cured (24+ hours) takes a strip of paint with it. Pull tape when the paint is dry to the touch but still flexible: typically 2 to 4 hours after the last coat. Pull at a 45-degree angle, slowly.
Pro tip: caulk the edge of the tape with a thin bead of clear caulk before painting. The caulk seals the tape edge so paint cannot bleed under it. Wipe excess caulk with a damp cloth, paint over the caulked tape, pull while still flexible. Knife-edge result every time.
7. Wrong paint finish for the room
This one is technically a product choice, not a prep step, but it shows up in the same six-month timeframe as the other mistakes and the consequence is similar (paint that fails or looks bad fast).
The honest sheen rules for Ottawa interiors:
- Bedrooms and main living areas: matte or eggshell. Hides drywall imperfections, looks soft, scrubs adequately for adult-traffic rooms.
- Hallways, kids' rooms, dining rooms: eggshell or satin. More scrubbable, slight sheen, hides minor scuffs.
- Kitchens and bathrooms: satin or semi-gloss. Moisture and grease tolerance, fully scrubbable, slight sheen.
- Trim and doors: semi-gloss or pearl. Durable, washable, takes the abuse trim takes.
- Ceilings: flat or matte ceiling-specific paint. Hides imperfections, no glare from overhead light.
The shortcut that fails: using flat paint everywhere because it looks uniform. Flat paint in a kitchen turns dingy in 6 months. Flat paint in a bathroom grows mildew. Flat paint on trim chips at the slightest brush-by.
Eighty percent of paint quality is in the prep. The actual painting is the easy part. If your prep is sloppy, no amount of expensive paint will save the finish.
The honest DIY paint call
Painting one bedroom: classic DIY territory. Two coats over clean walls, a weekend, a modest spend on paint and supplies. Worth every minute.
Painting a whole house: doable, but plan for two weeks of evenings and weekends, a meaningful paint budget, and one room you will redo because it taught you what you did wrong on the others.
Painting kitchen cabinets DIY: the highest-failure-rate paint job in Ottawa. The prep window is huge (degrease, sand, prime, sand again, prime again, topcoat, topcoat) and most homeowners cut three of those steps. Use a cabinet-specific paint like Benjamin Moore Advance and do the full prep, or pay a pro.
Painting trim DIY: harder than walls. Cuts are tighter, the surface needs sanding plus primer, and the finish shows every imperfection. Worth the investment in good tape and a quality angled sash brush.
The prep checklist
If you do nothing else from this article, do this list before any DIY paint job:
- Wash all surfaces with TSP substitute. Let dry.
- Inspect and recaulk every visible seam. Wait 24 hours before painting.
- Sand glossy surfaces with 220-grit until the sheen is dull. Vacuum dust.
- Prime patches, stains, and any previously-oil-painted surfaces with the right primer.
- Check the room temperature and humidity. Aim for 20 to 24 C and 50 to 60 percent RH.
- Use quality painter's tape. Apply to clean dry surfaces. Pull within 4 hours of final coat.
- Pick the right sheen for the room.
For paint included as part of a kitchen, bathroom, or basement renovation, our painters do the full prep without shortcuts. See our Ottawa home renovation page. Phone 613-862-4555 for a quote.