How to clean and prepare a house for exterior painting? (2026)
Quick Answer
To prepare a house for exterior painting, first inspect the outside for rot, loose paint, mould, dirt and failed sealant, then clean the surface thoroughly and let it dry properly. After that, scrape and sand loose coatings, repair defects, protect nearby areas, and only then move on to priming and painting with products suited to the surface and local weather.
Overview
Good exterior paintwork depends far more on preparation than on the final coat. Paint sticks best to a sound, clean, dry surface, so the job starts with inspection rather than opening a tin. Walk around the house and look for peeling paint, chalky residue, mildew, cobwebs, cracked caulk, damaged timber, rust stains, and any signs of water getting behind the cladding or trim. These problems need dealing with before painting, otherwise fresh paint can fail early. Cleaning removes the dirt, salts, mould and loose material that stop paint bonding properly. Depending on the surface and its condition, this may mean washing by hand or careful pressure washing, followed by enough drying time as stated by the paint manufacturer. Once clean and dry, remove all loose or flaking paint, feather rough edges, repair minor defects, and spot-prime bare areas with the correct primer. Preparation also includes practical site setup: covering plants, moving outdoor items, protecting paths and windows, and checking the weather forecast. Avoid painting over damp substrates or onto surfaces affected by active leaks. If you find widespread rot, lead paint risk, damaged render, or high-access areas, get specialist help before continuing.
Who this is for
Homeowners, landlords and capable DIYers preparing timber, masonry, fibre cement, metal trim or previously painted exterior surfaces before repainting.
What you’ll need
- stiff brush or soft exterior cleaning brush
- bucket and clean water
- suitable exterior house wash or cleaner approved for the surface
- garden hose or pressure washer used carefully if appropriate
- scraper or shave hook
- sandpaper or sanding block
- dust mask or respirator suitable for the task
- safety glasses and gloves
- drop sheets and masking materials
- filler or exterior repair compound suitable for the substrate
- exterior-grade caulk or sealant where appropriate
- primer matched to the surface and topcoat system
- ladder or access equipment suitable for safe exterior work
Before you start
Check the paint manufacturer's preparation instructions for your surface, and confirm the weather window, cleaning method and primer compatibility before starting. Test for lead if the house may have old paint layers, especially before scraping or sanding. Make sure gutters, downpipes and leaks are dealt with first, because paint will not solve moisture problems.
Step-by-step
- 1
Inspect the whole exterior carefully
Walk around all walls, trim, soffits, fascias, joinery and base areas. Look for peeling or blistering paint, powdery chalking, mould or algae, cracked sealant, rotten timber, rust, gaps around windows, damaged render, and any areas where water sits or enters. Mark defects so nothing is missed later.
Why: Inspection tells you whether the job is simple cleaning and repainting or whether repairs are needed first. Painting over moisture damage or failing substrate usually leads to early paint failure.
- 2
Protect the site and remove obstacles
Move outdoor furniture, pots, hoses and decorations away from the walls. Cover plants, paths, decks, lights and fittings as needed. Close windows, mask vulnerable areas, and switch off any exterior power where washing could create a hazard.
Why: Good protection speeds up the job and helps prevent damage from cleaning runoff, paint flakes and overspray.
- 3
Wash off dirt, mould, salts and loose residue
Clean the exterior using a method suitable for the surface and condition. Hand washing is gentler and often better for older or delicate areas; pressure washing can be useful if used carefully and at a setting and distance recommended by the equipment and paint manufacturer. Treat mould or mildew with an appropriate exterior cleaner, scrub where needed, and rinse thoroughly so no residue is left behind.
Why: Paint will not bond properly to grime, biological growth or chalky residue. Cleaning also reveals hidden defects that need repair.
- 4
Let the surface dry fully
After washing, allow the walls and trim to dry thoroughly before scraping, filling, priming or painting. Pay extra attention to shaded areas, end grain, joints and places near the ground where moisture lingers longest. Follow the paint system's label or technical data sheet for drying requirements.
Why: Trapped moisture can cause blistering, poor adhesion and mould returning under the paint film.
- 5
Remove failed paint and smooth the edges
Scrape off all loose, flaking or blistered paint until you reach a firm edge. Sand the remaining edges smooth so they do not telegraph through the finish. If the old coating may contain lead, stop dry scraping and sanding until you have checked the safe method required.
Why: New paint only lasts as long as the layer beneath it. Feathering edges helps the finish look even and reduces visible patching.
- 6
Repair defects and seal gaps
Replace rotten timber rather than filling over it. Repair small cracks, dents and minor surface damage with a product made for exterior use on that substrate. Re-caulk joints and gaps where movement is expected, but do not seal areas that are meant to drain or ventilate. Remove failed sealant before applying new material.
Why: Repairs create a stable base for paint and help keep water out of the building envelope without blocking designed ventilation paths.
- 7
Spot-prime bare or repaired areas
Prime exposed timber, patched areas, bare metal, repaired masonry, stains, and any surface the paint manufacturer says must be primed. Use a primer that matches both the substrate and the planned topcoat system. If the old paint is heavily weathered, a broader coat of primer may be needed.
Why: Primer improves adhesion, helps seal porous repairs, blocks some stains and evens out the surface so the topcoats perform consistently.
- 8
Do a final check before painting
Run your hand over the surface to check for dust, loose flakes, greasy patches or dampness. Confirm all repairs are sound, masking is in place, and weather conditions suit the paint system. Then start painting in the order recommended by the manufacturer.
Why: A final check catches the small issues that often cause visible defects or poor durability after painting.
Why this works
Exterior paint is a protective film, not a structural repair. It performs best when it can bond to a clean, dry, stable surface and when moisture is controlled before painting begins.
Common mistakes to avoid
- Painting over dirt, chalking, mould or salt deposits
- Using a pressure washer too aggressively and forcing water behind cladding or trim
- Skipping drying time after washing
- Leaving loose paint edges instead of scraping back to a sound surface
- Filling or painting over rotten timber instead of repairing it properly
- Using the wrong primer for bare wood, metal, masonry or patched areas
- Caulking drainage gaps or ventilation openings that should stay open
- Starting work without checking for possible lead paint in older coatings
Troubleshooting
Paint keeps flaking when scraped
Keep removing material until you reach firmly bonded paint. If failure is widespread, a larger strip-back or professional assessment may be needed.
Black or green staining returns after washing
Reclean with a suitable mould or algae treatment, rinse well, and address shade, leaks or constant dampness before painting.
Surface feels powdery after cleaning
Wash or brush again until chalking is removed as far as practical, then use the primer recommended for weathered surfaces.
Bare timber feels soft or spongy
Investigate for rot or moisture ingress. Replace damaged sections and fix the water source before painting.
Hairline cracks in render or masonry
Check whether they are superficial or moving. Use a compatible exterior repair system for minor stable cracks; get advice if cracks are significant or recurring.
Compare your options
Hand washing with brush and cleaner
Best for: Older houses, delicate surfaces, controlled cleaning around trim and joinery
Pros: Lower risk of driving water into the building, good control, often enough for maintenance repainting
Cons: Slower and more labour-intensive
Careful pressure washing
Best for: Sturdy surfaces with heavy dirt where the operator knows how to avoid damage
Pros: Faster removal of dirt and loose residue
Cons: Can gouge surfaces, strip sound paint, or force water behind cladding if used badly
Spot preparation only
Best for: Localised paint failure on an otherwise sound coating
Pros: Less work and less material use
Cons: Can give a patchy finish if surrounding paint is heavily weathered
Full wash, scrape, repair and prime programme
Best for: Tired exteriors with mixed defects or long-overdue repainting
Pros: Best base for durability and appearance
Cons: Takes longer and may reveal repairs that need professional attention
| Option | Best for | Pros | Cons |
|---|---|---|---|
| Hand washing with brush and cleaner | Older houses, delicate surfaces, controlled cleaning around trim and joinery | Lower risk of driving water into the building, good control, often enough for maintenance repainting | Slower and more labour-intensive |
| Careful pressure washing | Sturdy surfaces with heavy dirt where the operator knows how to avoid damage | Faster removal of dirt and loose residue | Can gouge surfaces, strip sound paint, or force water behind cladding if used badly |
| Spot preparation only | Localised paint failure on an otherwise sound coating | Less work and less material use | Can give a patchy finish if surrounding paint is heavily weathered |
| Full wash, scrape, repair and prime programme | Tired exteriors with mixed defects or long-overdue repainting | Best base for durability and appearance | Takes longer and may reveal repairs that need professional attention |
Alternatives
- Hire a painting contractor to carry out preparation and painting as one system
- Arrange professional washing and repair work, then do the painting yourself
- If the coating is failing extensively, consider a more complete strip-back approach recommended by a professional
Pro tips
- Start on the least visible elevation if you are unsure of your cleaning and preparation method.
- Take photos during inspection so you can compare before and after and track recurring damp spots.
- Clean from the top down so dirty water does not re-soil finished areas.
- Use separate tools for mouldy areas and clean them afterwards to avoid spreading spores.
- Label any repair products and primers used so you can match the paint system later.
Safety notes
- Wear eye protection, gloves and suitable respiratory protection when scraping, sanding or using cleaners.
- Treat old paint cautiously in case it contains lead; follow official lead-safe guidance before disturbing it.
- Use ladders and access equipment safely, on stable ground, and avoid overreaching.
- Keep cleaning chemicals and paint products away from children, pets and ponds or drains unless the product says disposal is safe that way.
- Do not use electrical equipment where washing could create a shock risk.
Legal & regulatory notes
Requirements for lead paint handling, waste disposal, runoff and scaffold or ladder safety can vary by location. Follow local council or national health and safety guidance, and check product labels for disposal instructions.
What this guide does not cover: This guide covers cleaning and preparation before exterior painting, not the full painting process, colour selection, detailed scaffold setup, or substrate-specific repair methods for major building defects.
Cost considerations
Preparation often takes more time than painting itself, but it is usually cheaper than repainting early because the coating failed. Costs rise if you uncover rot, rust, cracked render, lead paint, difficult access or moisture problems that need repair 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 these directories of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.
Frequently asked questions
Do I always need to pressure wash before exterior painting?+
No. Many houses can be prepared by hand washing with a suitable cleaner and a brush. Pressure washing can be effective, but it can also damage surfaces or force water behind cladding if used carelessly.
Can I paint over a little bit of peeling paint?+
No. Any loose or flaking paint should be removed back to a sound edge first, then the area should be sanded, repaired if needed, and primed as required.
Should I prime every wall or only bare patches?+
That depends on the condition of the existing coating and the paint system you are using. Bare areas nearly always need primer, and heavily weathered or repaired surfaces may need more extensive priming. Check the manufacturer's instructions.
What if I find mould on the exterior?+
Clean it with a suitable exterior treatment, rinse as directed, and address the cause of persistent dampness. Painting over untreated mould usually leads to staining and adhesion problems.
How do I know if old exterior paint might contain lead?+
Older homes are more likely to have lead in previous paint layers. Use a reliable test method or ask a professional before scraping or sanding, and follow official lead-safe guidance.
Sources & references
Guidance on this page is traced to documented sources. Last checked 25 September 2026.
- US EPA - Protect Your Family From Lead in Your Home · government
Supports caution around disturbing old paint that may contain lead and the need for lead-safe practices.
Core preparation methods change slowly, but product instructions, environmental rules and lead-safety guidance can vary by location and over time.