Painting & Decorating·Surface preparation

How to prepare walls for painting (2026)

Partially verified

Quick Answer

To prepare walls for painting, clear the area, clean the surface, repair any damage, sand where needed, deal with stains or mould, then prime bare or repaired patches before painting. Good preparation matters because paint sticks best to a sound, clean, dry surface and flaws usually show more once fresh paint goes on.

Overview

Proper wall preparation is the difference between a paint job that looks smooth and lasts well, and one that peels, flashes, cracks or shows every defect. The exact prep depends on the wall condition and the type of existing surface, but the basic order stays the same: inspect, clean, repair, smooth, remove dust and prime where needed. If you skip straight to painting, dirt, grease, loose paint or damp can stop the new coat bonding properly. Likewise, filler that has not been sanded flat or patch areas left unprimed often stand out after painting, especially in daylight or with matt finishes. Before starting, make sure the wall is dry and any underlying problems such as leaks, active damp or flaking plaster have been dealt with. Use the paint and filler manufacturer’s instructions for compatibility and drying times, because these vary by product. If the home may contain old lead-based paint, take extra care and follow official guidance before sanding or scraping. For most sound interior walls, preparation is mostly careful cleaning, local repairs and spot priming rather than heavy work. Taking time here usually saves both paint and rework later.

Who this is for

Homeowners, tenants with permission, landlords and DIY decorators preparing previously painted or plastered interior walls for repainting.

What you’ll need

Dust sheets or floor protection
Masking tape if needed
Step ladder if needed
Good lighting
Sugar soap or a suitable wall cleaner
Bucket, sponge or cloths
Filler suitable for the wall surface
Filling knife or scraper
Sandpaper or sanding sponge in suitable grades
Vacuum or soft brush for dust removal
Stain-blocking primer for water marks, smoke or other stains if needed
General primer or mist coat materials for bare plaster if needed, following the paint manufacturer’s instructions
Protective gloves
Eye protection
Suitable face mask if sanding dust is likely

Before you start

Check what surface you have: previously painted wall, new plaster, patched plaster, wallpaper residue, or an area affected by damp, mould or stains. Read the labels for your filler, primer and paint to confirm surface suitability, drying times and any need for a specific primer. If paint is flaking badly, plaster is loose, mould keeps returning, or there are signs of active leaks or damp, fix the cause before decorating. If the property is older and you suspect lead paint, avoid dry sanding until you have checked official safety guidance.

Step-by-step

1
Clear and protect the room
Move furniture away from the walls, cover floors and nearby items, and remove or loosen pictures, curtain fittings and socket faceplates where safe to do so. Mask edges you do not want to mark.
Why: Protection makes it easier to work thoroughly and reduces accidental damage, dust spread and paint splashes.
2
Inspect the wall carefully
Look across the wall in good light for cracks, nail holes, dents, flaking paint, greasy patches, water marks, mould, loose plaster or old wallpaper paste. Lightly run a scraper over suspect areas to find anything loose.
Why: Preparation only works if you identify the real problem first. Painting over loose or contaminated areas usually leads to poor adhesion and visible defects.
3
Clean the surface
Wash off dust, grease and general dirt with a suitable wall cleaner or sugar soap, following the product instructions. Rinse if the cleaner requires it, and allow the wall to dry fully. In kitchens, hallways and around switches, pay extra attention to greasy or hand-marked areas.
Why: Paint does not bond well to grease, grime or chalky dust. Cleaning helps the new coating stick evenly.
4
Remove loose material and repair damage
Scrape back any flaking paint, cut out unstable filler, and open fine cracks slightly if needed so repair material can key properly. Fill holes, dents and cracks with an appropriate filler, then let it dry as directed on the product label. If plaster is loose or crumbling rather than just marked, stop and repair the substrate before painting.
Why: Paint follows the surface underneath. Sound repairs stop old damage telegraphing through and reduce the risk of future peeling or cracking.
5
Sand the repaired and rough areas smooth
Once filler is fully dry, sand repaired spots flush with the wall and feather the edges of any scraped paint so there is no obvious ridge. On glossy existing paint, lightly abrade the surface if the new paint system requires it. Vacuum or wipe away all sanding dust afterwards.
Why: Sanding levels repairs and creates a surface the new paint can grip. Dust left behind can ruin the finish and weaken adhesion.
6
Treat stains, mould or bare areas appropriately
If there are water marks, smoke staining or similar discolouration, use a suitable stain-blocking primer. If there is mould, clean and treat it with an appropriate product and address the moisture source first. Prime bare plaster, filler patches or other porous areas using the primer or mist-coat approach recommended by your paint manufacturer.
Why: Stains can bleed through fresh paint, mould can return if the cause remains, and porous patches often absorb paint unevenly and show as dull or shiny 'flashing' without primer.
7
Do a final dust check and test the surface
Run your hand lightly over the wall to check for dust, rough spots or missed defects. Touch up any remaining filler or sanding as needed. Make sure the wall is dry, sound and uniformly prepared before opening the paint.
Why: A final check catches the small issues that become obvious only after the top coat goes on.

Why this works

Paint performs best when it can bond to a clean, dry, stable surface with an even porosity. Cleaning removes contamination, repairs restore a flat substrate, sanding smooths transitions and improves key, and primer controls absorption and blocks problem stains.

Common mistakes to avoid

Painting over dust, grease or nicotine staining without proper cleaning
Filling holes but not sanding them flush once dry
Skipping primer on bare plaster, filler patches or stains
Painting over active damp, mould or a leak before fixing the cause
Leaving loose or flaking paint in place
Using products without checking label instructions for compatibility and drying

Troubleshooting

Repaired patches show through the finish

Sand the edges smoother, remove dust and spot-prime the area before repainting.

New paint peels or scratches off easily

Check whether the wall was greasy, dusty or glossy. Remove loose paint, clean thoroughly, abrade if needed and use the correct primer before repainting.

Brown or yellow marks bleed through fresh paint

Let the surface dry if moisture is involved, then use a stain-blocking primer designed for the type of stain before recoating.

Mould comes back after painting

Treat the mould properly and address the underlying moisture, condensation or ventilation issue; repainting alone will not solve it.

Compare your options

Spot priming only repaired or bare patches

Best for: Sound previously painted walls with small local repairs

Pros: Less material, quicker, usually enough for minor patching

Cons: Can still show unevenness if the wall has many porous patches or colour variation

Priming the entire wall

Best for: Walls with many repairs, mixed surfaces, strong colour change or uncertain previous coatings

Pros: More even absorption and finish, better consistency

Cons: More time and material

Light cleaning and local sanding

Best for: Walls already in good condition

Pros: Fast and simple

Cons: Not enough if there are stains, grease, flaking paint or damaged plaster

Option	Best for	Pros	Cons
Spot priming only repaired or bare patches	Sound previously painted walls with small local repairs	Less material, quicker, usually enough for minor patching	Can still show unevenness if the wall has many porous patches or colour variation
Priming the entire wall	Walls with many repairs, mixed surfaces, strong colour change or uncertain previous coatings	More even absorption and finish, better consistency	More time and material
Light cleaning and local sanding	Walls already in good condition	Fast and simple	Not enough if there are stains, grease, flaking paint or damaged plaster

Alternatives

If the wall has extensive failed paint or multiple heavy layers, consider stripping back more thoroughly rather than patch-prepping isolated areas.
If walls are badly damaged or uneven, re-skimming by a plasterer may be better than repeated filling and sanding.

Pro tips

Use raking light from a lamp or window to reveal dents and ridges before painting.
Mark repaired areas lightly with low-tack tape until primed so you do not miss them.
Clean around light switches, door frames and radiator areas especially well, as these often hold grease and dust.
Keep one cloth just for the final dust wipe after sanding.

Safety notes

Ventilate the room well when cleaning, sanding, priming and painting.
Wear eye protection and a suitable mask when sanding to reduce dust exposure.
Take extra care with old paint in older homes, as it may contain lead; follow official guidance before scraping or sanding.
Use step ladders safely and avoid overreaching.

Legal & regulatory notes

If you are renting, check whether you have permission to redecorate. In older properties, especially where lead-based paint may be present, follow official health and safety guidance for safe preparation and waste handling.

What this guide does not cover: This guide covers general preparation for interior walls before painting. It does not cover exterior masonry preparation, wallpaper removal in detail, specialist coatings, or remediation of structural damp or serious plaster defects.

Cost considerations

Preparation usually costs less than repainting failures later. Better prep can reduce paint wastage and improve finish quality, but severe damp, mould recurrence, failed plaster or suspected lead paint can increase costs because the underlying issue should be dealt with first.

Prefer to hire a professional?

If this job is beyond a confident DIY — or the work needs to be done by a licensed professional — you can find a verified painter or decorator through Trade Directory (tradedirectory.co.nz), New Zealand's directory of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.

Find a painter or decorator on Trade Directory

Frequently asked questions

Do I need to wash walls before painting?+

Usually yes, especially if the wall may have grease, smoke residue, hand marks or dust. Even clean-looking walls often have contamination that affects adhesion.

Should I sand all walls before painting?+

Not always. Sound, matt walls may only need local sanding on repairs or rough spots. Glossy, patched or uneven surfaces often benefit from light abrasion, but follow the paint manufacturer’s guidance.

Can I paint straight onto filler?+

It is better to prime filler patches first if the paint system recommends it. Filler is often more porous than the surrounding wall, so unprimed patches can flash through the finish.

What if the wall has mould?+

Do not simply paint over it. Clean and treat the mould with a suitable product and fix the moisture or ventilation problem, otherwise it is likely to return.

Do new plaster walls need different preparation?+

Yes. New plaster must be fully dry and usually needs preparation exactly as recommended by the paint manufacturer, commonly involving a suitable first coat for bare plaster rather than standard top coat straight on.

Sources & references

Guidance on this page is traced to documented sources. Last checked 24 September 2026.

Crown Paints - How to prepare walls for painting · manufacturer
Supports cleaning, repairing defects, sanding and surface-specific preparation before painting.

Basic wall preparation methods change slowly, but product-specific primers, fillers and drying guidance vary by manufacturer.