1. Know what you are repairing
This guide covers shallow dents and small fixing holes in otherwise sound interior plaster or plasterboard. It does not cover large openings, failing plaster, fire-rated assemblies or structural cracks. A crack that widens, returns repeatedly or accompanies sticking doors deserves investigation before decoration.
Look for staining, softness, bubbling paint and a musty smell. Resolve a moisture source before filling; a patch cannot cure a leak. Older textured coatings and paints may contain hazardous substances. If the material’s history is uncertain, obtain appropriate advice before scraping or sanding. Avoid creating dust simply to discover what is underneath.
2. Choose the right filling material
Ready-mixed interior filler is convenient for isolated small defects and avoids measuring powder. Check the permitted depth per application and whether the product is suitable for your substrate. Powder fillers require mixing and have a limited working time, but some formulations suit deeper repairs. Follow the exact product instructions rather than treating these categories as interchangeable.
Flexible decorator’s caulk belongs in suitable moving joints, not as a broad sandable wall patch. Large holes usually need a supported plasterboard repair and an appropriate jointing system. If filler would be spanning an unsupported void beyond its stated limits, change the repair method.
3. Prepare a clean, stable edge
Protect the floor and move furniture clear. Gather a narrow filling knife, wider finishing knife, filler, suitable abrasive, sanding block, dust collection equipment, primer and matching paint. Use eye protection and respiratory protection appropriate to the material and dust; ventilation alone does not capture sanding dust.
Remove an old fixing carefully without tearing away sound wall material. Trim or scrape only loose edges that are safe to disturb. Remove dust using a suitable vacuum and the cleaning method recommended for the filler. Torn plasterboard paper may need a compatible sealing treatment first to prevent bubbling. Do not wet the area excessively.
4. Fill in controlled layers
Press filler into the defect so it contacts the sides rather than merely covering the opening. Draw the knife across the area to remove unnecessary excess. For a deeper hole, build layers within the product’s maximum depth, allowing each stage to dry or set as directed. Drying and chemical setting are not the same thing.
Keep the final application thin and feather it into the surrounding wall with a wider knife. A broad, shallow transition is easier to disguise than a small raised mound. Clean the knife between passes; dried crumbs dragged through fresh filler create avoidable grooves.
5. Let it dry, then refine the surface
Follow the manufacturer’s drying guidance and allow extra time in cool or humid rooms. A pale surface can still conceal damp material underneath. Painting early may trap moisture or produce a visible patch. Do not use concentrated heat to force the process.
Once ready, sand lightly with a block and a fine abrasive suitable for the filler. The aim is to remove ridges, not hollow out the centre or abrade the surrounding paper. Use a light held at a shallow angle to reveal high edges. If the repair is low, apply another thin layer rather than sanding the whole wall down to it.
6. Prime before judging the colour
Remove sanding residue and apply a primer compatible with the patch and existing coating. Filler often absorbs paint differently from an already painted wall, creating a dull or shiny outline called flashing. Primer helps equalise absorption but does not flatten a poorly shaped repair.
Use the original paint if it remains sound and you know its finish. Even then, ageing and application texture can make a touch-up visible. Match the roller texture where possible and assess the dry result in daylight and artificial light. Repainting the complete wall from corner to corner usually gives a more consistent appearance than repeatedly enlarging a touch-up.