How to Prep Walls for Painting: A Toronto Painter''s Checklist

Quick Answer
Prep decides how long your paint lasts, not the brand on the can. Fill (spackling under 1/4 inch, joint compound for anything bigger), sand 120 then 220, vacuum with HEPA, wipe with a damp microfibre, prime patches and stains with the right primer (Fresh Start for new drywall, Zinsser BIN for stains, STIX for glossy), then roll two coats of finish. Pros spend 50 to 70% of project time on prep (MPI Standards, 2024). Skip it and you save an afternoon, then watch the job fail at 18 months.

I'm Chad Caglak, and I've been painting Toronto homes for 20 years. The question I hear most isn't about colour or budget. It's "Do I really have to do all this prep?"

Yes.

I'll tell you why with one job. A couple in High Park asked me to repaint a kitchen the previous painter had finished six months earlier. Grease ghosts everywhere, brush drag at every cut-in, and the paint was peeling above the stove in sheets you could lift with a fingernail. Nobody had degreased. Nobody had primed. The walls got two coats of mid-grade satin straight onto a film of vaporized canola oil. We washed it down with Krud Kutter, hit the stove wall with STIX, and the job that should have lasted eight years had to be redone in eighteen months. The paint wasn't the problem. The prep was. What follows is the checklist we actually use on Toronto interiors. Not the version that looks pretty in a brochure.

Key Takeaways

• Prep eats 50 to 70% of total project time on a pro job (MPI Standards, 2024).
• Sand drywall mud twice: 120 grit to flatten, 220 grit to finish before primer.
• "Paint and primer in one" is a marketing line, not a real substitute for Fresh Start, BIN, or STIX.
• Picture-framing comes from cutting in once and rolling twice. Cut in twice and the defect goes away.
• Occupied-condo dust control needs HEPA vac, plastic sheeting, and a box fan pulling negative pressure.

Why does prep matter more than paint choice?

Roughly 70% of residential paint-failure callbacks trace back to surface prep, per MPI field data (Master Painters Institute, 2024). The substrate is what decides if the film bonds, levels, and lasts. Premium paint over a dusty or glossy wall peels in months. Two coats of Regal Select on properly prepped drywall holds 8 to 10 years.

Citation capsule: Wall preparation drives 70% of paint job longevity outcomes, with MPI's Architectural Painting Specification Manual naming inadequate surface prep as the leading cause of premature coating failure (MPI, 2024). Toronto humidity swings make that number worse, especially on plaster.

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Here's the other thing prep buys you, and nobody talks about it. Clean sequencing. When the wall is filled, sanded flat, and dust-free, the cut-in flows, the roller loads evenly, and your second coat actually builds the film you wanted. Skip prep and the painter spends the day fighting the wall instead of laying paint on it.

What is the picture-framing defect and how does prep prevent it?

Picture-framing, what most painters call boxing, shows up as a darker frame around every door, window, and ceiling line a few weeks after the job is done. The cause is brushing the cut-in once while rolling the field twice. The perimeter ends up with half the film thickness of the middle. Two cut-in passes, plus clean prep, kills it. Citation capsule: Picture-framing, also called boxing, is the trade term for the perimeter sheen and colour difference that appears when brushed cut-ins get one coat and rolled fields get two. The fix, documented by PDCA and most premium paint TDS sheets, is to cut in twice so the film build matches across the entire wall.

Here's the prep link most homeowners miss. If the wall is dusty or has chalky old paint along the cut line, the brush drags. The painter thins the cut to compensate. Now the framing problem gets worse. Clean, dust-free, properly primed edges let the brush lay a full first cut that matches what the roller will put down.

If you want the deep technical breakdown of this defect, read our companion piece on why cutting in twice separates pros from rollers. It pairs with this prep guide.

paint finishes explained

What is the real primer decision tree (Fresh Start vs BIN vs STIX)?

No single primer covers every problem. Three of them handle roughly 95% of residential situations. Benjamin Moore Fresh Start 046 for new drywall and spot priming. Zinsser BIN shellac for stains and odours. INSL-X STIX for glossy, chalky, or hard-to-coat surfaces. Each runs $55 to $85 CAD per gallon and does one job well. Citation capsule: Benjamin Moore Fresh Start 046 is a 100% acrylic, low-VOC primer-sealer recommended for new drywall, patched areas, and uniform sheen prep (Benjamin Moore, 2026). Zinsser BIN is a shellac-based stain killer that seals water marks, smoke, tannin, and pet odours in one coat (Rust-Oleum Zinsser, 2024). STIX is a urethane-modified bonding primer for glossy and chalky surfaces.

When to use Fresh Start 046

Reach for Fresh Start on new drywall, skim-coated repairs, patches, and any dark-to-light colour change. It seals the gypsum face paper, evens out sheen between mud and old paint, and gives two coats of finish a uniform base to sit on. About $58 CAD per gallon at most Toronto BM dealers.

When to use Zinsser BIN

BIN is for water stains, smoke damage, tannin bleed (cedar, pine knots, old varnish), pet urine, and any odour you need locked down. Shellac binds contaminants that latex primers cannot stop. It dries in 45 minutes, smells like denatured alcohol, and you need ventilation when you spray it. About $42 CAD per quart.

When to use STIX bonding primer

STIX is the answer for glossy oil-painted trim, semi-gloss kitchen walls, chalky old plaster, tile, and laminate. Anywhere adhesion is the failure mode rather than porosity. It bonds without heavy sanding, though I still scuff-sand with 220 first because I trust mechanical tooth as much as chemistry. About $72 CAD per gallon. Converting glossy oil trim to white is the classic Toronto job, see our trim, baseboard and door painting cost guide.

The myth I'd happily retire: "Paint and primer in one" is marketing for slightly thicker paint. It covers a previously painted wall in decent shape with one extra coat. It will not seal new drywall, block stains, or bond to glossy trim. For any of that, you need a real primer. Aura vs Regal vs Ben vs Ultra Spec

How do you sand drywall mud properly (grit progression)?

Sand drywall mud in two passes. 120 grit to flatten filler ridges within 24 hours of drying, then 220 grit for the final pass right before primer. USG's drywall finishing guide lists this as the baseline for a Level 4 finish, which is what residential walls need under eggshell or satin (USG, 2023). Skip the 220 and scratch marks will telegraph through sheen.

Citation capsule: USG's Gypsum Construction Handbook specifies 120 to 150 grit for initial joint compound sanding and 220 grit for the final pre-primer pass to hit a Level 4 drywall finish suitable for flat, eggshell, and satin paints (USG, 2023). Coarser grit alone leaves visible scratch patterns under low-angle light.

Why two passes matter

The 120 pass cuts down the proud edges where the mud sits above the surrounding paper. It's aggressive, fast, and throws the heaviest dust. The 220 pass smooths the 120 scratches and feathers the mud edge into the paper so nothing telegraphs under primer. One pass at 220 takes forever and clogs the paper. One pass at 120 leaves marks. Two passes is the move.

What sheen demands what finish level

Flat and matte hide minor imperfections. Eggshell starts to show mud ridges under raking light. Satin and semi-gloss show every scratch. If you're going eggshell or higher, the 220 final pass is mandatory. That's also why prep for sheen-flashing prevention matters, which is the next section.

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Why does prep matter for sheen flashing prevention?

Sheen flashing is the reflectivity difference between primed patches and the surrounding old paint, and it shows up hard in eggshell, satin, and semi-gloss. The fix is to prime the whole wall, not just the patches, so the absorption rate matches edge to edge. Spot-priming a satin job is the number-one reason I get the "the wall looks blotchy" phone call. Citation capsule: Sheen flashing happens when the substrate's absorption rate varies across a wall, causing finish paint to dry with different reflectivity in different areas. Master Painters Institute prep standards recommend full-wall priming, not spot priming, on any surface receiving an eggshell or higher sheen finish (MPI, 2024).

Matte hides, eggshell reveals

Flat and matte scatter light, so small absorption differences disappear. Eggshell, satin, and semi-gloss reflect light directionally, so an unprimed patch in the middle of old paint dries with a visible halo. The patch goes duller because the bare gypsum or fresh mud pulled moisture out of the paint faster than the surrounding wall did.

The full-prime fix

On any wall going eggshell or higher, prime the whole wall after patching. Not just the repairs. That's 45 minutes per room and one extra gallon of primer ($58 CAD). It saves you from sheen flashing that no second coat will fix. I default to full priming on every kitchen, bathroom, and trim job we touch.

paint finishes explained

When do you use TSP versus a degreaser on kitchen walls?

Citrus degreaser (Krud Kutter or Simple Green) handles standard kitchen grease. Pull out TSP (trisodium phosphate) only for heavy nicotine, smoke residue, chalky exterior paint, or a glossy surface you want to dull without sanding. TSP is harsher, needs a thorough rinse, and is phosphate-restricted in many municipalities for environmental reasons (Health Canada, 2023).

Citation capsule: TSP (trisodium phosphate) is a heavy-duty alkaline cleaner that etches paint slightly to aid adhesion, but it leaves residue and is phosphate-restricted in many Canadian jurisdictions. Modern citrus degreasers handle typical kitchen grease without etching or rinsing requirements, which makes them the default for routine kitchen prep.

Degreaser for routine prep

For 90% of Toronto kitchens, a spray-on degreaser plus a clean-water microfibre wipe does the job. Spray, wait 60 seconds, wipe with a damp cloth, follow with a clean-water wipe to lift the residue, let dry. About 20 minutes per kitchen wall.

TSP for problem walls

Reach for TSP-PF (phosphate-free, legal in Ontario) when you have nicotine staining, smoke residue, or you're repainting old oil-based semi-gloss without sanding. Gloves and eye protection on, rinse twice, let the wall dry overnight before you prime. Skip the rinse and the film left behind will wreck adhesion under your primer.

How do you control dust in an occupied condo during prep?

Run a HEPA shop vac at the source while sanding, seal the work area with 6-mil plastic and painter's tape, and pull negative pressure with a box fan exhausting through a cracked window. Three layers, working together, keep drywall dust in the work area and out of the condo's return-air system (CDC Lead Renovation Guidance, 2023). Citation capsule: Drywall sanding generates respirable silica dust that travels through HVAC return vents within hours in an occupied condo. A HEPA vacuum at the sanding point, sealed plastic containment, and a negative-pressure box-fan exhaust setup cuts airborne dust by 85 to 95% versus passive containment alone, based on EPA RRP guidelines.

The three-layer condo dust setup

1. HEPA shop vac at the tool. A Festool, Bosch, or Ridgid shop vac with HEPA filter, hooked straight to the sanding pole or block. Catches 99% of dust at source. About $250 to $600 CAD for a quality unit.
2. Plastic sheeting at the doorway. 6-mil plastic taped floor-to-ceiling across the doorway, zipper door if you have multiple entries. Tape plastic over the HVAC supply and return vents inside the work area.
3. Negative-pressure box fan. Box fan in the window facing out, window cracked open behind it, every other window closed. The fan pulls air and any escaped dust out of the work area instead of pushing it into the rest of the unit.

That's the exact setup I run on every occupied condo job in CityPlace, Liberty Village, and Yorkville. Without it, the building manager gets calls about dust in the hallway within 48 hours and your client is the one fielding them.

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What is the step-by-step prep checklist?

Seven steps, every interior, every substrate. Each one has a job, and skipping any of them shows up later in a step that depends on it. Plan on 4 to 12 hours per bedroom depending on wall condition.

Step 1: Inspect under raking light

Hang a work light low on one wall before anything else moves. Side light reveals every nail pop, crack, dent, and stain that overhead light hides. Walk the room, list every defect, decide what gets filled, sanded, primed, or replaced. Skip this and you'll find problems after the second coat dries.

Look for holes, cracks (hairline versus deep), water stains, loose paint, glossy finishes, wallpaper, grease, smoke residue, and any sign of mould or moisture. In Toronto homes built before 1960, pay close attention to the ceiling-to-wall plaster seams.

Step 2: Clear and mask

Pop the outlet covers, switch plates, curtain rods, hooks, anything screwed to the wall. Move furniture to the centre, cover with canvas drop cloths (canvas doesn't slide like plastic). Mask ceiling lines, trim, and floors with quality painter's tape, FrogTape or 3M ScotchBlue. Cheap tape bleeds.

Step 3: Fill holes and damage

• Nail holes and small dings (under 1/4 inch): Paintable spackling like DAP Fast 'N Final. Overfill by 10%, let dry 30 min to 2 hours, sand 120 then 220.
• Larger holes (1/4 to 1/2 inch): Two thin coats of spackling instead of one thick one. Thick coats shrink and crack.
• Large holes and gouges (over 1/2 inch): Joint compound with a backing patch or mesh tape. Three thin coats, sand between each.
• Cracks at seams: Paintable acrylic latex caulk, not spackling. Caulk flexes. Spackling cracks again. If the same crack reopens every season no matter how you fill it, the problem is movement, not your patch, and our guide on why hairline cracks keep coming back walks through the permanent fix.
• Plaster damage: Plaster patching compound (Plaster of Paris or Durabond setting compound), not regular drywall mud.

Step 4: Sand in two grit passes

First pass at 120 to knock down the proud edges of filler. Second pass at 220 for the final feather before primer. Hand-sand most walls with a foam block. Power sanders on plaster or older drywall throw divots and clouds of dust that you'll regret for the rest of the job.

For glossy or semi-gloss surfaces, scuff-sand with 220 just to break the shine, then prime with STIX. You're not removing the paint, you're creating tooth for the primer to grip.

Step 5: HEPA vacuum and damp wipe

Vacuum every wall, baseboard, and corner with a HEPA shop vac and a brush attachment. Don't sweep. Sweeping aerosolizes the dust and it lands back on your walls inside an hour. After vacuuming, wipe walls with a barely damp microfibre cloth. Not wet, just enough to lift residual dust.

Let the walls dry fully (15 to 30 minutes depending on humidity) before primer.

Step 6: Caulk gaps and seams

After filling, scan for cracks at ceiling lines, around trim, and in inside corners. Run a bead of paintable acrylic latex caulk, smooth with a wet finger or caulking tool, wipe excess right away. Cure 1 to 2 hours before primer. DAP Alex Plus is the standard pick at about $5 CAD per tube.

Step 7: Prime where it matters

Prime patches, stains, glossy areas, dark-to-light transitions, bare drywall, and the whole wall on any eggshell-or-higher job. Match the primer to the problem:

• Fresh Start 046 for new drywall and patches
• Zinsser BIN for water stains, smoke, tannin, odour
• STIX for glossy, chalky, or hard-to-coat surfaces

One real primer coat plus two finish coats beats three finish coats over nothing. Every time.

What does each substrate need (drywall, plaster, concrete)?

Toronto homes span 150 years of construction, and each substrate wants different prep. Drywall (post-1960) is forgiving. Plaster (pre-1960 Annex, Roncesvalles, Leslieville) is brittle and needs plaster-specific patching. Concrete (basements, garage walls) is porous, alkaline, and needs a masonry primer or the latex will peel off in months.

Modern drywall (post-1980 builds)

Fill with spackling or joint compound, sand 120 then 220, prime patches with Fresh Start, two coats finish. Most North York, Scarborough, Mississauga, and Markham homes fall here. Standard prep timeline.

Plaster (Victorian, Edwardian, pre-1960)

Plaster is harder and more brittle than drywall. Hand-sand only, 120 to 150 grit. Plaster-specific patching compound, not drywall mud, because drywall mud doesn't grip lath. Prime with Fresh Start or, on chalky surfaces, STIX. Budget 20 to 30% more prep time than the equivalent drywall job.

Tap the walls before you sand. Hollow spots mean the plaster is separating from the lath behind it, which is a structural repair, not a paint job.

Concrete (basements, garage walls)

Concrete is porous and alkaline (pH 12 to 13 when new). Latex applied directly fails inside a few months. Prep means a moisture check (tape a 12-inch plastic square to the wall for 48 hours; condensation means you have a moisture problem), a degreaser wash, full drying, then a masonry primer like Benjamin Moore Super Spec Masonry Primer.

How long does prep actually take?

Prep takes 50 to 70% of total project time on a pro paint job, per MPI labour-allocation guidance (MPI, 2024). The exact number depends on wall condition and substrate. Here are the brackets I use to quote Toronto jobs in CAD. Citation capsule: Professional painters spend 50 to 70% of total project hours on surface preparation, with the remaining 30 to 50% on primer and finish application. The ratio holds across residential interior, exterior, and commercial work, and skipping prep is the leading cause of paint-job warranty claims.

DIY hours usually double these numbers. Pros move faster because they know spackling dry times, primer recoat windows, and how to sequence two rooms so neither one sits idle.

What does professional prep actually cost in Toronto?

Pro wall prep adds $400 to $1,200 CAD in labour to a single-room paint job, depending on wall condition. Whole-house interior prep runs $2,500 to $6,000 CAD in labour alone before any paint goes on. Materials add $150 to $400 per room. These are 2026 Toronto-market rates, cross-checked against our cost-to-paint-a-house Toronto guide. The trade-off is real. Heavy prep adds 30 to 50% to project cost and roughly triples job lifespan. A $4,000 job with proper prep holds 8 to 10 years. A $2,800 cut-rate job fails in 18 to 30 months. On a per-year basis, proper prep is the cheaper option.

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When should you call a pro instead of DIYing prep?

Call a pro when prep climbs past 20 hours, when you find plaster separation, when there's mould or water damage, or when the home is pre-1978 and triggers lead-paint testing. At that point, pro labour is usually cheaper than your time plus the cost of fixing the mistakes. Specifically, get a pro for:

• Extensive plaster repair or loose plaster (structural stabilization)
• Drywall damage bigger than 4 by 4 inches (cut-out and patch by someone with reps)
• Water damage or visible mould (root-cause investigation first)
• Popcorn ceiling removal (asbestos testing required in pre-1980 Toronto homes)
• Pre-1978 homes (Health Canada lead-paint testing required on any renovation disturbing painted surfaces, per CDC RRP framework)

We do prep, drywall, and paint across Toronto through our interior painting service and our specialized drywall repair and painting line.

The short version

Wall prep doesn't show up in before-and-after photos. It shows up 18 months later, when the paint either holds or fails. I spend 50 to 70% of project time on prep because picture-framing, sheen flashing, and peeling all trace back to the same skipped steps.

Fill in thin coats. Sand 120 then 220. Vacuum with HEPA. Match the primer to the problem (Fresh Start, BIN, or STIX). Roll two real coats of finish. That's the whole game.

If you're planning to paint your Toronto home, give prep the time it deserves, or hand it to someone who will.

Get a quote

If prep is more than you want to tackle, fair enough. Some homeowners DIY it, some hire it out.

We handle wall prep and painting for Toronto houses, condos, and anything needing specialized drywall repair. Named painters on every project, two-coat baseline, real primer where it matters.

Get your free 24-hour quote or call (416) 875-8706.

We work across downtown Toronto, North York, Etobicoke, Scarborough, Mississauga, and the rest of the GTA.

Chad Caglak, Co-Owner, Home Painters Pro