How to Prepare Walls for Painting: The Steps That Actually Matter

Preparation is the majority of a professional paint job — not in the sense that it takes slightly longer, but in the sense that the preparation determines the result and the painting confirms it. Done correctly, proper wall preparation can help a paint job last for many years. Skipped, the same surface may fail far earlier than it should.

Here are the steps, what each does, and which ones you genuinely cannot skip.

For professional wall preparation and repainting, see our interior painting service.

Step 1 — Clean the Surface

What it does: Removes contaminants that prevent adhesion. Grease, silicone, wax, soap residue and household cleaning product build-up are often invisible but will cause the new paint coat to fail to bond.

What to use:

• Interior walls: sugar soap solution applied with a sponge, rinsed with clean water. Pay particular attention to kitchen walls, around doors and light switches (where skin oils accumulate), and bathroom walls.
• Previously painted gloss surfaces: wipe down with a degreasing agent before sanding.
• Exterior surfaces: high-pressure wash. For mould-affected exterior surfaces, biocide treatment before washing.

Can you skip it? No. Contaminated surfaces can produce premature adhesion failure. In kitchens and bathrooms, grease, soap residue, moisture and cleaning-product build-up are common reasons paint fails earlier than expected.

Step 2 — Repair Cracks, Holes and Surface Damage

What it does: Creates a flat, sound surface for the paint to sit on. Paint follows the surface — it doesn’t fill defects.

What to use:

• Hairline cracks: flexible acrylic filler or caulk. Do not use rigid filler for cracks that may move — it will re-crack through the new paint coat.
• Larger cracks and holes: plaster filler for walls and ceilings. Apply in layers for deep holes — filler shrinks as it dries and a deep single-fill application will crack and pull away from the edges.
• Between wall and trim (where the paint has shrunk away): paintable flexible caulk, not filler.

Can you skip it? For minor surface work, yes — not all walls have significant defects. For visible cracks and holes, skipping this produces a finish that shows the defects through the new paint.

Important: In older homes, especially pre-1970 properties, existing paint may contain lead. If lead-based paint is suspected, testing or a specialist assessment may be needed before sanding, scraping, or stripping. Lead paint removal and abatement should be handled by appropriately qualified specialists.

Step 3 — Sand

What it does: Two purposes, depending on the surface:

1. Creates a mechanical key for adhesion — particularly important on gloss surfaces and previously painted surfaces where the new coat needs something to grip.

2. Smooths filler repairs to flush with the surrounding surface — visible filler edges that weren’t sanded will show through paint.

What to use:

• Gloss existing paint: 120-grit to scuff the surface
• Plaster filler repairs: 120-grit to level, 180-220 grit to smooth
• Previously painted flat surfaces in good condition: light 180-grit scuff is sufficient

Can you skip it? On flat surfaces in good condition, being repainted with the same product type — often yes. On gloss surfaces, over filler repairs or where you’re applying water-based over oil-based paint — no.

Step 4 — Remove Dust

What it does: Sanding dust and plaster dust contaminate the surface and create adhesion problems identical to grease contamination. They also create texture in the finish — grit embedded in the paint coat.

What to use: Tack cloth (a sticky cloth designed to remove fine dust before painting) or a slightly damp cloth, then allow to fully dry.

Can you skip it? No — particularly after sanding. The amount of dust that is invisible to the eye yet still affects the paint surface is greater than most people realise.

Step 5 — Prime

What it does: Priming serves three functions:

1. Seals porous surfaces so the topcoat goes on evenly without uneven absorption

2. Provides an adhesion layer appropriate to the substrate

3. Blocks stains and bleed-through (water marks, tannin from timber, mould staining)

When you need primer:

• Any bare plaster, raw MDF or timber surfaces
• After significant plaster repairs — the filler repairs are more absorbent than the surrounding surface and will appear as dull patches through the topcoat without primer
• Where you’re changing from oil-based to water-based paint systems
• Over water staining or mould-affected areas — the cause should be addressed first, the surface should be properly cleaned or treated, and an appropriate stain-blocking primer may be needed rather than a standard primer
• On laminate or non-porous surfaces where adhesion is a concern

When you can skip primer:

Repainting an existing painted surface in good condition in the same paint system — often primer is unnecessary on sound, flat, degreased surfaces

Can you skip it? On sound existing paintwork being recoated in the same product type — often yes. Over fresh plaster, repairs or staining — no.

Step 6 — Apply First Coat and Re-sand

What it does: The first coat often reveals surface imperfections not visible on the bare surface — particularly tool marks from filler, ridges from crack repairs, and minor undulations. Light sanding after the first coat (180-220 grit, very light) smooths these before the final coat.

Can you skip it? For walls with minor imperfections, going to a low-sheen finish — sometimes. For high-quality finishes, semi-gloss surfaces and anywhere that will be seen in raking light (along a hallway, near windows) — this step produces a noticeably better result.

When Wall Preparation Becomes a Professional Job

Basic cleaning, small nail holes and light sanding can be manageable for simple DIY repainting. Preparation becomes more technical when there are water stains, mould staining, peeling paint, glossy old coatings, large plaster repairs, movement cracks, smoke staining or older paint systems that may contain lead.

In those cases, the preparation method matters as much as the paint itself. Using the wrong filler, skipping primer, sanding an unsafe coating or painting over contamination can cause the new finish to fail early.

The Preparation vs Painting Time Reality

A professional painter preparing and painting a standard bedroom (4 walls plus ceiling) typically spends:

• Preparation (cleaning, filling, sanding, priming): 3–5 hours
• Painting (two coats): 2–4 hours

Preparation takes longer than painting. On larger interior jobs with significant repair work, the ratio shifts further toward preparation. This is where the cost of a professional job goes — and why a low-price quote that doesn’t mention preparation is a warning sign.

If paint is already bubbling, peeling or failing early, see our guides on why paint fails early and why paint peels off walls.

Wall Preparation FAQs

Do I need to wash walls before painting?

Yes. Dust, grease, soap residue, and cleaning-product buildup can prevent new paint from bonding properly. Kitchens, bathrooms, doors and light-switch areas usually need the most attention.

Do I need to sand walls before painting?

Not always. Sound flat paint may only need light preparation, but gloss surfaces, filler repairs, rough areas and old coatings usually need sanding or scuffing so the new paint can adhere properly.

Do I need primer before painting walls?

Primer is usually needed on bare plaster, raw timber, MDF, significant filler repairs, stains, mould-affected areas after treatment, and surfaces where adhesion is uncertain. Sound existing paint in good condition may not always need primer.

Can I paint over peeling paint?

No. Loose or peeling paint should be removed back to a sound edge before repainting. Painting over failing paint usually causes the new coating to peel along with the old one.

For interior painting with preparation clearly included in the scope, Request a Free Written Quote.

Melbourne Renovation Experts provides preparation-first interior painting across South East Melbourne. Based in Glen Waverley, with no subcontractors and written fixed-price quotes.