How to Prep Walls for Painting

September 15, 2026

How to Prep Walls for Painting

How to Prep Walls for Painting

A step-by-step guide for Canadian homeowners who want a smooth, long-lasting finish

A fresh coat of paint can transform a room in a single weekend — but the secret to a professional-looking finish isn’t the paint itself, it’s what happens before the roller ever touches the wall. Skipping prep work for painting walls is the number one reason DIY paint jobs peel, crack, or look patchy within months, especially in Canadian homes that deal with dry winter air and humid summers.

At Star Painting, we’ve prepped thousands of walls across Toronto, Mississauga, and Scarborough, and the process below is exactly what our crews follow on every job. Whether you’re painting one accent wall or an entire home, here’s how to get it right.

Why Prepping Walls for Paint Actually Matters

Paint doesn’t stick well to dust, grease, or glossy surfaces. Without proper prep, you’ll likely see:

• Peeling or bubbling paint within the first year
• Visible brush and roller marks
• Uneven sheen once the paint dries
• Paint that chips easily around doors, switches, and corners

Taking a few extra hours to prep now saves you from repainting the same wall again next season.

Step 1: Clear the Room and Protect Your Space

Before anything else, move furniture to the centre of the room or out entirely, and cover floors and remaining furniture with drop cloths. Remove outlet covers, switch plates, and any wall hardware or curtain rods. It’s much easier to paint (and clean up) an empty, protected room than to work around obstacles.

Step 2: How to Clean Walls Before Painting

This is the step most homeowners rush through, and it’s the one that matters most. Paint needs a clean, dry surface to bond to — dust, cobwebs, cooking grease, and handprints will all show through your finish or cause the paint to lift later.

Here’s how to clean walls before painting the right way:

1. Dust first. Use a dry microfiber cloth, a soft-bristle brush, or the brush attachment on your vacuum to remove loose dust and cobwebs from the entire wall, including corners and ceiling lines.
2. Wash with a mild solution. Mix a few drops of dish soap or a dedicated TSP (trisodium phosphate) substitute with warm water. TSP or TSP-free cleaners are especially useful in kitchens, bathrooms, and around light switches where grease and skin oils build up.
3. Spot-treat grease and stains. For kitchens near cooking areas or bathrooms with soap scum, go over problem spots a second time with a slightly stronger solution or a degreaser made for interior walls.
4. Rinse with clean water. Any leftover soap residue can prevent paint from adhering properly, so wipe the walls down again with a clean, damp cloth or sponge.
5. Let walls dry completely. In Canadian homes, especially basements or bathrooms, this can take longer than expected due to humidity. Give walls at least a few hours — overnight is safer — before moving to the next step. Painting over damp drywall is one of the most common causes of adhesion failure.

Step 3: Repair Cracks, Holes, and Imperfections

Once the wall is clean and dry, inspect it closely under a bright light (raking light from the side reveals imperfections paint alone won’t hide).

• Fill nail holes, small dents, and hairline cracks with spackle or lightweight filler.
• For larger holes or drywall damage, use a patching compound and let it cure fully according to the product’s instructions — rushing this step leads to visible bumps later.
• Sand any patched areas smooth once dry (more on sanding below).

Step 4: Sanding Walls Before Painting

Sanding walls before painting isn’t just for repaired spots — it’s an important step for the whole surface, especially if the walls have a glossy or semi-gloss finish, visible texture, or old paint drips.

What to sand and why:

• Patched areas need light sanding (120–150 grit) so repairs blend seamlessly with the surrounding wall.
• Glossy or semi-gloss paint should be lightly sanded to “de-gloss” the surface, giving new paint something to grip onto.
• Textured or uneven walls may need a light pass to knock down high spots or old brush ridges.

After sanding, dust will settle back onto the wall — this is why the cleaning and sanding steps often need to happen together, finishing with one more wipe-down using a tack cloth or slightly damp rag before priming.

Step 5: Protect Trim, Ceilings, and Edges

Apply painter’s tape along baseboards, window and door trim, and ceiling lines. Press the edges down firmly to prevent bleed-through, and use a putty knife to seal the tape edge for the crispest lines possible.

Step 6: Prime (Don’t Skip It)

Primer isn’t optional if you’re:

• Painting over a dark or bold colour with a lighter one
• Covering bare drywall, patched areas, or wood
• Dealing with stains, smoke damage, or water marks
• Painting a basement or humid area where mildew has been treated

A quality primer evens out the surface, helps your paint colour appear truer, and often means one fewer coat of the actual paint is needed.

A Canadian-Specific Tip: Watch the Humidity

Because Canadian homes swing between dry winter heating and humid summer months, walls — especially in basements — can hold more moisture than they appear to. Always check that walls are fully dry before painting, and if you’re prepping a basement, run a dehumidifier for a day or two beforehand for the best results.

When to Call in the Professionals

Proper wall prep takes real time — often as long as the painting itself — which is why many homeowners choose to bring in professionals for larger rooms, basements, or whole-home projects. At Star Painting, every job starts with the same thorough prep process outlined above: cleaning, repairing, sanding, and priming, so the finished paint job looks better and lasts longer.

Planning a painting project in Toronto, Mississauga, or Scarborough? Request a free quote and our team will handle the prep work and painting from start to finish.