Painting & Decorating·Exterior paint

How to prepare exterior walls for painting (2026)

Verified from sources

Quick Answer

Prepare exterior walls for painting in this order: inspect, clean, remove loose material, repair defects, let the wall dry, then prime where needed before painting. Good preparation matters more than the topcoat, because paint sticks properly only to a sound, clean, dry surface.

Overview

Exterior wall preparation is mainly about giving new paint a stable surface to bond to and stopping existing defects from showing through. The correct order matters: if you repair before cleaning, dirt and chalk can stop fillers, sealants or primers from adhering; if you paint before the wall is fully dry, moisture can become trapped and lead to blistering, peeling or staining. Start by checking the wall condition and identifying the substrate, such as masonry, render, cement, brick or previously painted surfaces. Then wash off dirt, biological growth, chalking and pollutants. Once clean, scrape away anything loose or flaking, sand rough edges, and treat any mould or algae according to the product instructions. Repair cracks, failed joints and small holes with materials suitable for exterior use and the wall type, then allow repairs to cure and the wall to dry as directed by the manufacturer. Prime bare, repaired or porous areas if the paint system calls for it. A wall is ready when it is visibly clean, feels sound, has no loose paint or powdery residue, repairs are firm and flush, and the surface condition matches the primer and paint manufacturer’s instructions.

Who this is for

Homeowners, landlords and maintenance staff preparing exterior masonry or previously painted walls before repainting.

What you’ll need

Stiff brush or broom
Bucket and clean water
Mild exterior cleaner or fungicidal wash suitable for the surface
Scraper
Wire brush if appropriate for the substrate
Sandpaper or sanding block
Exterior filler or repair mortar suitable for the wall type
Exterior-grade sealant for joints if needed
Primer or stabilising solution if specified by the paint system
Dust sheets and masking materials
Ladder or access equipment suitable for the height
Personal protective equipment appropriate to the task

Before you start

Check the weather window, because exterior preparation and painting should be done only when the wall can dry properly and conditions suit the products you are using. Read the paint, primer, cleaner and filler labels for substrate suitability, drying times and overcoating guidance. Confirm whether the existing coating is sound enough to paint over, and check for underlying damp, leaks, structural cracking or failing render; preparation alone will not solve those defects.

Step-by-step

1
Inspect the wall and identify defects
Walk the whole elevation and look for flaking paint, chalky residue, dirt, algae, mould, efflorescence, cracks, hollow render, failed joints, stains and signs of damp. Rub the existing painted surface with your hand to see if it leaves powder, and press suspect areas to find anything loose or drummy.
Why: Inspection tells you whether the problem is just surface contamination or a deeper failure. If the substrate is unsound, new paint will fail even if the colour coat is applied neatly.
2
Clean the surface thoroughly
Brush off loose dirt and cobwebs, then wash the wall with a suitable exterior cleaner or according to the paint manufacturer’s preparation advice. Remove biological growth fully rather than painting over it. If using a pressure washer, use it carefully so you do not drive water into the wall or damage render, mortar joints or soft masonry.
Why: Paint and primer need direct contact with the surface. Dirt, grease, salts, chalking and organic growth interfere with adhesion and can cause staining or early failure.
3
Remove all loose, flaking or weak material
Scrape off loose paint, friable render edges and anything not firmly bonded. Feather the edges of sound surrounding paint by sanding so there is not a hard ridge. Brush away all dust created by scraping and sanding.
Why: New paint cannot secure loose material beneath it. Feathering edges helps the finish look even and reduces visible patching through the topcoat.
4
Treat defects and make repairs
Fill small cracks and holes with an exterior repair product suitable for the substrate. Rake out and refill only where the product instructions say this is appropriate. Renew failed sealant at movement joints and around openings if needed, using a compatible exterior sealant. If render is hollow, badly cracked or detached, remove and repair it properly rather than filling over the surface.
Why: Repairs restore a continuous surface, stop water entry and prevent cracks or gaps telegraphing through the finished paint.
5
Allow repairs and the wall to dry properly
Let washed surfaces, treated areas and repairs dry and cure fully for the period stated on the relevant product labels. Do not rush this stage, especially after cleaning, rain, or deeper repairs.
Why: Moisture trapped under paint is a common cause of blistering, peeling, patchiness and masonry staining. Uncured filler or mortar can also affect adhesion and finish.
6
Prime bare, repaired or porous areas
Apply the correct primer, stabiliser or sealer only where the paint system requires it, following the manufacturer’s guidance for the substrate and condition. Typical candidates are bare masonry, chalky but sound surfaces after preparation, patched areas and very porous repairs.
Why: Primer evens out porosity, improves adhesion and helps the finish coat dry and cover more consistently.
7
Do a final readiness check
Before painting, make sure the wall is clean, dry, dust-free and uniformly sound. Run your hand over prepared areas: they should not shed loose powder, and repaired patches should feel firm and level. Tape, protect adjacent surfaces and confirm the weather remains suitable for the painting stage.
Why: A final check catches the small issues that most often spoil exterior paint jobs, such as residual dust, damp patches or missed loose edges.

Why this works

Exterior paint performs best when it bonds to a stable substrate with controlled porosity and no trapped moisture. Preparation removes weak layers, repairs entry points for water and creates a surface the primer and topcoat can adhere to evenly.

Common mistakes to avoid

Painting over dirt, chalking, algae or flaking paint
Skipping the drying stage after washing or repairs
Using filler, sealant or primer that is not suitable for exterior use or the wall type
Assuming paint will hide cracks, hollow render or damp problems
Over-aggressive pressure washing that damages masonry or forces water behind the surface

Troubleshooting

The wall still feels powdery after cleaning

Clean again and remove as much chalking as possible, then use a suitable stabilising or binding primer only if the paint manufacturer allows it for that surface condition.

Hairline cracks keep showing after filling

Check whether the crack is moving or linked to a deeper substrate issue. Use the repair method recommended for exterior masonry and seek professional advice if cracking is recurring or widening.

Dark patches suggest damp rather than surface dirt

Pause preparation for painting and find the moisture source, such as leaks, failed pointing, bridging or penetrating damp. Let the wall dry only after the cause is fixed.

Previous paint peels off in large sheets when scraped

Remove all poorly bonded coating back to a sound edge. Widespread failure often means full stripping or much more extensive preparation is needed before repainting.

Compare your options

Hand cleaning and scraping

Best for: Small areas, delicate surfaces, and targeted defect removal

Pros: More control, lower risk of water ingress or surface damage, good for careful inspection

Cons: Slower and more labour-intensive

Careful pressure washing

Best for: Heavily soiled robust masonry where the manufacturer accepts this method

Pros: Faster dirt removal over large areas

Cons: Can damage render, mortar or coatings and can saturate the wall if used badly

Spot priming only

Best for: Mostly sound previously painted walls with localised bare or repaired patches

Pros: Uses less material and avoids unnecessary build-up

Cons: Patchiness can show through if porosity differences are not properly controlled

Full-surface primer or stabiliser

Best for: Uniformly porous, weathered or borderline surfaces where the paint system recommends it

Pros: More consistent absorption and adhesion

Cons: Extra time and material, and unnecessary use can be wasteful if not actually required

Option	Best for	Pros	Cons
Hand cleaning and scraping	Small areas, delicate surfaces, and targeted defect removal	More control, lower risk of water ingress or surface damage, good for careful inspection	Slower and more labour-intensive
Careful pressure washing	Heavily soiled robust masonry where the manufacturer accepts this method	Faster dirt removal over large areas	Can damage render, mortar or coatings and can saturate the wall if used badly
Spot priming only	Mostly sound previously painted walls with localised bare or repaired patches	Uses less material and avoids unnecessary build-up	Patchiness can show through if porosity differences are not properly controlled
Full-surface primer or stabiliser	Uniformly porous, weathered or borderline surfaces where the paint system recommends it	More consistent absorption and adhesion	Extra time and material, and unnecessary use can be wasteful if not actually required

Alternatives

If the wall has widespread hollow or failed render, consider render repair or replacement before any painting work
If the existing coating is badly degraded, complete coating removal may be more reliable than patch preparation

Pro tips

Prepare one elevation at a time so cleaned surfaces do not get dirty again before painting
Keep a written note of the products used so the primer, filler and topcoat remain compatible
Check shaded and north-facing walls carefully for algae and mould, as growth is often less obvious there
Feather scraped edges well; this often makes more difference to the final appearance than extra paint

Safety notes

Use ladders and access equipment safely and only on stable ground
Wear eye protection, gloves and suitable respiratory protection when scraping, sanding or using chemical cleaners
Take extra care with older coatings; if you suspect hazardous materials in old paint, get specialist advice before disturbing it
Protect nearby plants, paths, windows and metalwork from cleaners, dust and debris

Legal & regulatory notes

Local rules may apply to access equipment, work at height, waste disposal and disturbance of hazardous coatings. If you are working on a listed building, in a conservation area, on shared property, or using contractors, check the relevant local authority and property requirements first.

What this guide does not cover: This guide covers general preparation of exterior walls before painting and does not replace the instructions for your specific cleaner, repair products, primer and paint. It does not cover specialist substrates, full render replacement, structural repairs or diagnosis of building defects in depth.

Cost considerations

Preparation often takes more time than painting itself, but it is usually the cheapest place to avoid premature failure. Cleaning, repairs and correct priming can reduce the risk of repainting again early because of peeling or patchy finish.

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 always need a primer on exterior walls?+

Not always. Sound previously painted surfaces may only need spot priming, while bare, repaired, porous or chalky surfaces often need a suitable primer or stabiliser. Follow the paint manufacturer’s system guidance.

Can I paint over small cracks?+

Only if the paint system specifically states it can bridge that type of crack, and the substrate is otherwise sound. In most cases, cracks should be properly repaired first.

How do I know the wall is dry enough to paint?+

The surface should look dry, feel dry and have had the drying or curing period required by the cleaner, filler, primer and paint manufacturers. If there is any doubt after rain, washing or repairs, wait longer.

Should I wash off all old paint?+

No, only loose or failing paint needs removing. Sound, well-adhered paint can usually stay if it is clean, properly prepared and compatible with the new system.

Is pressure washing necessary?+

No. It can be useful on some robust surfaces, but brushing and washing by hand is often safer for older render, weak mortar joints or delicate masonry.

Sources & references

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

Dulux Trade - Exterior Surface Preparation · manufacturer
Supports the need to clean, remove defective coatings, repair surfaces, ensure dryness and use appropriate primers for exterior painting.
Crown Paints Professional - Preparation · manufacturer
Supports the principle that preparation is essential, including cleaning, removing loose material, repairing defects and matching preparation to substrate condition.
Health and Safety Executive - Working at height · government
Supports safety guidance on planning and carrying out exterior wall preparation using ladders or other access equipment.

The basic preparation sequence changes slowly, but exact product compatibility and drying guidance depend on the specific paint system and manufacturer instructions.