Inspect the wall and remove loose or poorly bonded paint. Fill cracks and holes and sand repaired areas smooth.
Grease and dust can reduce adhesion. Light sanding can help when the existing finish is very glossy.
Whether primer is needed depends on the surface condition, old and new paint systems and the size of the color change.
Inspect the old coating first
Look for blisters, powdering, grease and moisture marks. Sound paint may not need complete removal, but loose layers cannot support a new finish. After a washed surface dries, dull glossy areas with an appropriate method, remove loose material and smooth repairs.
Work in sequence
Protect furniture, clean, repair defects, remove sanding dust and choose a primer for the substrate. A small trial area helps assess compatibility with the existing coating. Paint will not solve a continuing moisture source. If the composition of an old finish is unknown, assess hazardous-dust risks before abrasive removal.
Before coating
- Confirm the surface is dry, sound and free of dust.
- Match repair materials and primer to the substrate.
- Check waiting times for each layer in its own instructions.
Must the entire wall be primed?
That depends on the substrate and product. Local repairs, differing absorption and weak coatings affect the primer requirement. Do not automatically use the same approach for sound old paint and fresh filler.