Painting Over Old Paint: How to Prepare the Surface

Repainting isn't one job. A sound wall that just needs a fresh colour, a wall with a few damaged patches, and a wall whose old paint has turned powdery all need different preparation. Treating them the same is how new paint ends up failing early.

First: damp and cracks

Before choosing a preparation, check for damp or leaks and for cracks whose cause is unknown or concerning. Both are resolved or assessed before decorating. See Damp Walls Before Painting: What to Do First and Wall Preparation Before Painting in Kenya.

Sound surface: clean, dull and repaint

If the old paint is firm and sound, preparation is light: the surface should be dry, clean and free from shine. Kenyan manufacturers' guidance is to dull glossy surfaces by sanding so the new paint can grip. If you're unsure whether the new paint suits the old coating, for example water-based paint over an old oil-based finish, test a small patch first.

Local defects: fill and prepare

Small holes, dents, damaged patches and cracks already judged cosmetic are filled and sanded smooth, then the wall gets a preparation coat and finish coats. Local filling is not full-wall skimming: a few defects don't turn a sound wall into a skimming job.

Loose, flaking or peeling paint

All loose and flaking paint must be removed, by scraping or sanding, back to a sound edge before repainting. Paint applied over loose paint comes away with it. Peeling has several possible causes, so check for moisture before repainting: see Why Is My Paint Peeling?. Once the loose paint is off, look at what's left: sound surfaces continue as above; powdery ones need the next section.

Chalky or powdery surfaces

Some old surfaces are loosely bound: they are chalky, powdery or crumbly. Old cement paint, distemper and limewash are common examples. Emulsion applied straight onto them tends to fail early through loss of adhesion. Kenyan technical guidance is to remove the loose material and apply a penetrating primer to bind the surface before emulsion.

This needs a different preparation system, so FinishGrid doesn't yet calculate paint quantity or cost for chalky or powdery areas. A painter can confirm the surface and quote for it.

Planning the paint

For sound walls and walls with local defects, the Paint Calculator works out how much paint to buy. Leave chalky or powdery areas, and anything on hold, out of the calculation.