Interior Painting Prep: The Checklist That Makes Paint Last

On a proper repaint, more of the crew's hours go into preparation than into rolling colour. That surprises people until they understand what paint actually is: a thin film, a fraction of a millimetre thick, that can only ever be as sound as the surface underneath it. Grease, dust, loose old paint, unfilled cracks — the film faithfully records all of it, then fails at exactly those spots.

Prep is also where GTA painting prices split. Whole-home rates run $1.80–$3.00 per square foot of wall area at the basic end and $2.50–$4.50 with fuller prep as of 2026, and that gap is almost entirely hours of washing, filling, sanding, priming, and caulking. Two painters using the identical paint can deliver jobs that look the same on day one and completely different by year two.

This post lays out the sequence we expect from any professional crew — ours or anyone else's — so you can read a painting quote and know what you are actually buying.

Professional prep runs in a fixed order, because each step protects the next:

• Wash. Walls collect hand oils, cooking residue, and dust film — especially kitchens, bathrooms, and anywhere near a return-air grille. Paint will not bond through it. Degrease and rinse first, always.
• Fill. Nail holes, anchor holes, dents, and gouges get filled with proper compound — not caulk — and slightly overfilled to allow for shrinkage.
• Sand. Filled spots are sanded flush and glossy old surfaces are scuffed so new paint has something to grip. A quick pole-sand of full walls knocks down old roller texture.
• Spot-prime. Every patch, stain, and bare spot gets primer; some situations need full-wall priming (next section).
• Caulk. Gaps where trim meets wall get a fresh flexible bead, cutting the shadow lines that make even freshly painted rooms look tired.

Then — and only then — two full coats of finish colour. Compressing this sequence is the main way a cheap quote gets cheap.

If you own a home built in the last two decades in Milton, Vaughan, Oakville's newer streets, or anywhere in the 2000s-boom GTA, you know the pattern: hairline cracks over doorways, nail pops marching down a hallway wall. This is normal — new framing lumber dries and moves for years after construction — but the repair has to respect the cause.

A nail pop needs the fastener dealt with: drive or replace it, add a drywall screw beside it, then fill, sand, and prime. A settlement crack needs to be opened slightly, taped with mesh, and coated with compound feathered wide. The lazy version — smearing filler or caulk across the crack and painting over it — telegraphs back through the new paint within a season, because the underlying movement never stopped.

Older housing stock fails differently. Pre-war plaster in Toronto's east-end Victorians and Hamilton's Durand-area homes develops loose sections where the plaster keys have broken; those need reattachment or skim-coating, not spot filler. Where walls are rough overall, taping-and-mudding work runs $1.75–$3.75 per square foot, and a full skim to a smooth Level 5 surface adds roughly $1.00–$1.50 per square foot — real money that buys genuinely flat walls.

"Paint and primer in one" is the most misunderstood label in the paint aisle. Self-priming paints work on sound, clean, previously painted walls in a similar colour. Everywhere else, actual primer earns its step.

Prime every patch and every area of bare drywall compound — unprimed patches absorb paint differently and "flash" as dull spots under evening light. Prime over stains with a dedicated stain-blocking primer; water marks, marker, and tannin bleed straight through ordinary paint, one coat after another. Prime glossy surfaces — old oil-painted trim in pre-1990s homes especially — with a bonding primer, or the new coat can peel off in sheets. And prime tinted when making a dramatic dark-to-light change; one coat of grey-tinted primer routinely saves two coats of expensive finish paint.

Skipping is legitimate exactly once: sound, washed, scuff-sanded walls getting a similar colour in the same sheen. On everything else, a quote that never mentions primer is telling you something about year two.

We see the after-photos of cheap paint jobs when we are hired to fix them, and the failures are predictable enough to catalogue.

Peeling above the shower and behind the stove: paint went over soap film or grease without washing. Dull rectangles that show up in raking afternoon light: unprimed patches flashing through the finish. Cracks reopened along the same lines as before: filler smeared over moving cracks instead of taped repairs. Caulk lines splitting at the baseboards within months: old dried caulk painted over instead of cut out and replaced. Paint pulling off the trim when the painter's tape came off: gloss surfaces never scuffed or bonded.

Ontario's climate accelerates all of it. Humid summers load indoor air with moisture, winter turns exterior walls cold — and in the GTA's older uninsulated double-brick homes, condensation forms on those cold wall surfaces all season. Marginal adhesion that might survive in a stable climate fails here first, usually on the north wall of a bathroom or a kitchen.

None of these are paint-quality failures. Every one is a prep failure wearing new paint.

You now have the checklist — use it as a reading tool. A professional quote names its prep: washing, a patching allowance, sanding, the primer product and where it goes, re-caulking of trim. A quote that jumps straight from "two coats premium paint" to a low price has simply moved the prep from the job to your future. It is the painting-specific version of the red flags we look for in any contractor, and the scope detail belongs in writing just like any renovation contract.

Two safety items belong in this conversation for GTA housing stock. Homes built before about 1980 can carry lead-based paint on old trim and walls — it should never be dry-sanded or scraped without proper containment. And drywall compound and textured ceilings from before about 1990 may contain asbestos; lab testing runs $300–$800 and comes before sanding or scraping old surfaces, not after. A crew that shrugs at either question is the wrong crew.

Choose the quote that describes the work under the paint, even when it is not the cheapest. And if your repaint is part of something larger — new floors, moved walls, a whole-home renovation — talk to us early so prep and painting land in the right spot in the schedule, after the dust and before the furniture.