Here's a truth that every professional painter knows: preparation is 80% of a good paint job. The actual painting is the easy part.

If you've ever seen paint peeling, bubbling, or flaking off a wall within months, poor preparation is almost always the cause — not the paint itself. Whether you're painting a brand-new building or repainting old walls, this guide covers everything you need to know.

Hero image: A worker sanding/preparing a wall for painting — showing the preparation process

Why Wall Preparation Matters

Paint needs a clean, dry, smooth, and stable surface to adhere properly. Without preparation:

New block walls absorb paint unevenly, wasting product and creating a patchy finish
Old painted walls with flaking paint cause new paint to peel off with the old layers
Damp walls cause blistering and mould growth under the new paint
Dusty walls prevent proper adhesion — the paint bonds to dust, not the wall

Spending an extra day on preparation can mean the difference between a paint job that lasts 2 years and one that lasts 7+ years.

Tools and Materials You'll Need

Item	Purpose
Wire brush or scraper	Remove flaking old paint
Sandpaper (80, 120, 240 grit)	Smooth surfaces and key glossy areas
Filler / Wall putty	Fill cracks, holes, and imperfections
Putty knife / Filling knife	Apply and smooth filler
Clean water + sponge	Wash walls to remove dust and dirt
Masking tape	Protect edges, switches, and door frames
Drop cloths / nylon sheeting	Protect floors and furniture
Primer / Undercoat	Seal surface before topcoat

Image: Flat lay of wall preparation tools — scraper, sandpaper, filler, putty knife, primer tin

Preparing New Block Walls (Unpainted)

New block walls fresh from the builder require specific preparation:

Step 1: Allow Proper Curing Time

New cement/mortar must cure for at least 4–6 weeks before painting. Fresh cement is alkaline and contains moisture that will cause paint to fail.

In a rush? If you must paint sooner, use a specialised alkali-resistant primer that can handle residual moisture.

Step 2: Remove Surface Deposits

New walls often have:

Efflorescence — white powdery salt deposits
Cement splashes — lumps from the building process
Dust and sand from construction

Use a wire brush to scrub off efflorescence and a scraper for cement lumps. Then sweep or blow off all loose dust.

Step 3: Wash the Walls

Wash walls with clean water using a sponge. This removes fine dust that brushing missed. Allow walls to dry completely (24–48 hours in Nigerian weather).

Step 4: Apply Filler Where Needed

Inspect for:

Cracks along block joints
Holes from scaffolding nails
Uneven rendering

Mix wall filler according to instructions and apply with a putty knife. Overfill slightly — you'll sand it smooth once dry.

Step 5: Sand Smooth

Once filler is dry (2–4 hours), sand the filled areas smooth with 120-grit sandpaper. Lightly sand the entire wall to create a uniform surface. Wipe off dust with a damp cloth.

Step 6: Apply Primer

This is the most important step. Primer:

Seals the porous surface
Reduces paint consumption by 30–40%
Provides a uniform base for even colour coverage
Improves adhesion of the topcoat

Apply one generous coat of Kasha Universal Primer and allow to dry fully (4–6 hours).

Step 7: Paint!

Once the primer is dry, your wall is ready for topcoat application.

Image: Side-by-side — half of a new block wall unprimed (patchy) vs. primed (uniform)

Preparing Old Painted Walls (Repaint)

Repainting requires extra steps to deal with the existing paint layer:

Step 1: Assess the Existing Paint

Is it in good condition? (no peeling, no cracks) → Light sand, clean, and paint over it
Is it flaking/peeling? → Remove all loose paint back to a stable surface
Is it glossy? → Must be sanded to provide a key for new paint

Step 2: Remove Loose and Flaking Paint

Use a scraper or wire brush to remove all paint that's lifting, bubbling, or flaking. Be thorough — if you paint over loose paint, it will all come off together.

Step 3: Sand the Edges

Where old paint meets bare wall, sand the edges to create a smooth, gradual transition. This prevents visible "lips" showing through the new paint.

Step 4: Wash the Walls

Wash with water and a mild detergent (or sugar soap if available). This removes:

Grease and cooking oil residue (especially in kitchens)
Dirt and handprints
Cobwebs and dust

Rinse with clean water and allow to dry completely.

Step 5: Fill and Repair

Fill any cracks, nail holes, or damaged areas with wall filler. Sand smooth once dry.

Step 6: Spot-Prime Bare Areas

Any area where you've scraped back to bare wall needs a coat of primer. You don't need to prime the entire wall if the existing paint is in good condition — just the bare patches.

Step 7: Apply Your Topcoat

Start painting with your chosen emulsion. Two coats for best results.

Dealing with Damp and Mould

Damp walls are the number one enemy of paint in Nigeria's humid climate. Never paint over damp walls — the paint will blister and peel, and mould will grow behind it.

Identifying Damp

Dark patches on walls
White salt deposits (efflorescence)
Musty smell
Visible mould (black or green spots)
Paint bubbling or peeling

How to Fix Damp Before Painting

1. Find and fix the source:

Leaking pipes behind walls
Rising damp from the floor (no damp-proof course)
Rain penetration through cracks or failed exterior paint
Condensation from poor ventilation

2. Treat the affected area:

Scrape off all affected paint and loose plaster
Apply an anti-mould wash or diluted bleach solution (1 part bleach to 3 parts water)
Let it sit for 30 minutes, then scrub with a stiff brush
Rinse with clean water and allow to dry completely (several days if badly affected)

3. Apply a damp-seal primer before repainting

Warning: If the source of damp isn't fixed, no amount of paint or treatment will solve the problem. Fix the leak/drainage issue first.

Image: Wall showing damp damage — mould spots, peeling paint, efflorescence — as a "what to look for" reference

Common Preparation Mistakes

1. Painting Over Dust

Even a thin layer of dust prevents paint from bonding to the wall. Always wash walls before painting.

2. Painting Too Soon After Plastering

Fresh plaster/rendering contains moisture and is highly alkaline. Give it 4–6 weeks minimum. Painting too soon causes white patches, blistering, and peeling.

3. Using No Primer

Skipping primer on new walls means:

The first coat of paint is essentially the primer (wasted)
Uneven absorption creates patchy colour
Overall you'll need more paint, costing more in total

4. Ignoring Cracks

Paint doesn't fill or hide cracks — it stretches over them temporarily, then the cracks reappear. Fill them properly with putty.

5. Painting in High Humidity or Rain

If it's raining or humidity is extremely high, paint dries too slowly and may not cure properly. Paint on dry days.

Quick Reference: Preparation Checklist

[ ] Surface is dry (no damp, no recent rain)
[ ] All loose/flaking paint removed
[ ] Cracks and holes filled and sanded
[ ] Surface washed and dust-free
[ ] Edges and fixtures masked with tape
[ ] Floor/furniture protected with drop cloths
[ ] Primer applied on bare/new surfaces
[ ] Primer fully dry before topcoat

Get Professional Help

Not sure about the condition of your walls? At Kasha Paints, we offer professional painting services — including full wall preparation.

View our products — including Kasha Universal Primer
Get a free quote — we'll assess your walls and recommend the right approach
Chat on WhatsApp — send us a photo of your walls for quick advice

Kasha Paints — Giving value to your money.