Prep Guide: Stripping Old Paint Before Recoating

Stripping is only necessary when the existing film is failing. Where it is sound, sanding and painting over it is faster and more durable. The decision is a physical test, not a judgement call — and if the building predates 1978, it is a lead test first.

Substrate

Old paint

Full cure

7 days

Touch dry

4 hours

Steps

6

Strip or paint over: the test

Press a strip of low-tack tape firmly onto the wall, wait five minutes, and pull it off at 90 degrees. Then press a thumbnail into the film at eye height.

Result	Verdict	Action
Tape pulls off paint flakes	Failing	Strip back to the sound edge and feather
Thumbnail leaves a dent	Soft, probably oil-based and still curing	Wait 30 days, or strip
Film is hard, tape is clean	Sound	Wash, sand with P180, paint over
Chalking — powder on the finger	Binder has broken down	Strip; paint will not adhere to chalk

Painting over sound old paint is not a shortcut. It is the standard method, and the old film often provides better adhesion on a friable substrate than a fresh primer would.

Lead paint: test first, always

Buildings completed before 1978 may contain lead paint, which is most likely on timber trim, doors and windows rather than on walls, but it appears on all of them. Sanding, burning or dry-scraping lead paint produces airborne dust and fume that is a genuine health risk, particularly to children and pregnant women.

• Test with a swab before disturbing any paint. They are cheap, take two minutes, and give a yes/no answer.
• If it is positive, do not sand, do not use a blowtorch, and do not dry-scrape. Use a chemical stripper that is rated for lead paint, lay dust sheets, and seal the room from the rest of the house while you work.
• Where the coating is intact and you simply want to change colour, the safest route is to overcoat it rather than remove it.
• This site describes general methods only. Lead paint removal is regulated in most countries, and where the area is large the work should go to a certified contractor. Follow your local rules.

Working method for a chemical strip

1. Work one square metre at a time, from the top down, so drips land on unpainted film rather than on the strip you have just finished.
2. If the film is more than 0.5 mm thick, score it in a crosshatch with a knife so the stripper can reach the layers underneath.
3. Apply a thick coat of stripper and cover it with cling film or a purpose-made cover sheet. The cover is what keeps the solvent working; uncovered stripper skins over in ten minutes and does almost nothing.
4. Wait the full dwell time on the tin — usually 20-40 minutes — then lift the softened film in one pass with a flexible 35 mm knife. Two thin passes smear the residue back into the surface.
5. Neutralise with clean water, changing it often, and let the surface dry 24 hours. Residual stripper will soften the new paint from underneath.
6. Sand with P120 to remove the last of the residue, then P180 to flatten, fill any defects, and spot-prime.

Where this takes the longest

Corners between two painted surfaces — a window reveal, the junction of a door frame and a wall — take roughly as long as the flat area around them. Budget for it rather than fighting it: a 300 mm strip along every edge, done properly, often decides whether the job looks finished.

Dry time before recoating after a strip is longer than after a normal wash: 24 hours minimum, and 48 hours in a cold room, because water has gone into the substrate as well as into the old film.

What matters here

• Strip only failing film — test with tape and a thumbnail, then decide.
• Test for lead before disturbing any paint on a pre-1978 building.
• Cover chemical stripper with film; uncovered it skins over in ten minutes.
• Lift softened film in one pass; two thin passes push residue into the surface.

Elsewhere on this wall

• Prep Guide: First Coat on New Plasterboard