Identify the surface and follow the current instructions for your exact products. Do not sand or strip uncertain old coatings. Read the safety guide before disturbing materials.
Filler and caulk do different jobs
Use a suitable sandable filler for a small, stable wall defect. Use a compatible paintable caulk for a narrow joint where trim meets a wall and a little movement is expected. Caulk is not a substitute for a flat wall repair. Ordinary silicone is generally not paintable.
Check the maximum fill depth, drying time and whether the product is intended for indoors, outdoors or timber. Old lime plaster may need a compatible lime repair rather than an off the shelf gypsum filler.
Make a sound repair
Only work on a safe, dry and stable substrate. A loose edge will not become reliable because you put filler over it.
- Clean the area and remove only loose, safe material following the filler instructions.
- Press filler into the defect rather than bridging an empty cavity.
- Build deeper repairs in permitted layers or use a product rated for the full depth.
- Allow the repair to dry through, then sand only as required.
- Remove dust and prime or seal the repair as specified to prevent patchy absorption.
Read a recurring crack
A crack that opens again may reflect movement, a failed joint or damp. Repeatedly filling it is not a diagnosis. Photograph it with a date and scale and seek advice if it widens, appears suddenly or comes with sticking doors, bulging surfaces or other changes.
Allow caulk its stated time before painting. A skin on the surface does not mean the whole bead is ready; early coating can cause crazing or discolouration.
Common mistakes
- Using silicone under a painted finish.
- Leaving a thick ridge of filler and trying to sand it all away.
- Painting damp filler because its surface has turned pale.
Widening cracks, significant movement, loose ceilings and persistent moisture need diagnosis before cosmetic repair.
Sources & further reading
Original general guidance from Aethos, informed by the resources below. These references cover relevant safety, materials or techniques, not a specification for your property. Product examples are not paid recommendations.
- This Old House: how to paint a room (opens in a new tab)
Preparation and room painting technique. US products and terminology do not always translate directly to UK specifications.
- SPAB: limewash (opens in a new tab)
Traditional finishes, suitable substrates and caring for older buildings.