To prepare damaged walls for painting, work out what kind of damage you have before you open a tub of filler. Some damage is only skin-deep and can be filled. Some needs repairing first, such as a cracked plasterboard joint, a hole through the board or plaster that has come away from the brickwork. And some has a cause that is still active, such as damp or movement. Deal with causes first, then repairs, then filling and sealing, and check the wall under a low, raking light before any finish coat goes on.
That order matters more than the products. Most repairs that show through new paint were filled in the wrong order or too early, not with the wrong filler. The routine surface work of washing, scraping, filling, sanding and priming a tired wall is set out on our wall preparation and filling page. This guide covers what changes when the wall is actually damaged.
Sort the damage before you start
Walk round the room with a torch held flat against each wall and note everything you find. Then put each item into one of three groups.
| What you find | Group | What it needs before decorating |
|---|---|---|
| Small holes, dents, hairline cracks, old fixing holes | Surface | Fill, sand flush and spot-prime |
| A fine crack along the wall-to-ceiling line or beside skirting that reappears after filling | Surface (a moving joint) | Flexible decorators’ caulk, not filler |
| Screw heads pushing through, or a crack running dead straight along a plasterboard joint | Repair | Refix or re-tape the board, then fill |
| A hole right through plasterboard, a broken external corner, board that dents when pressed | Repair | Patch or replace a section of board |
| Plaster that sounds hollow when tapped, or bulges | Repair | Cut back the loose plaster and make good |
| A stain that is still damp, or mould that keeps coming back | Cause | Find and fix the moisture, then let the wall dry |
| A crack that is widening, runs diagonally from a door or window corner, or reopens after filling | Cause | Have it assessed before decorating |
If anything lands in the Cause group, decorating is the last step rather than the first. Paint over an active leak or a moving crack and the damage will be back, often within weeks.
In older properties, check what the existing coatings are before anyone sands. Lead paint and some older textured coatings need a different approach, and our interior painting preparation checklist explains what to look for.
Damage that catches people out
Cracks need opening up, not covering over
Filler smeared across a fine crack sits on the surface and tends to crack again along the same line. A crack holds filler better when it is raked out first: loose material is scraped away and the edges are opened slightly into a shallow V, so the filler has something to grip. Dust is brushed out before filling, and a dry, porous crack may need dampening or sealing so the filler does not dry out too fast.
If a crack has come back more than once, find out whether it is moving before you fill it again. A pencil mark at each end with the date beside it is a simple record: if the crack grows past the marks or visibly widens over a few weeks, it needs looking at by a surveyor or structural engineer rather than a decorator. Fine crazing across a whole wall is a different problem. Filling every line is slow, and lining paper is often the more practical answer.
Torn plasterboard paper
Stripping wallpaper or pulling off old tape can tear through the face of plasterboard and expose the brown paper layer beneath. Water-based filler or emulsion applied straight onto that layer soaks in, and the paper bubbles and lifts. Loose paper is cut away with a sharp knife, then the torn area is sealed with a primer suitable for damaged plasterboard before any filling. Oil-based and shellac-based primers are commonly used for this; check the manufacturer’s guidance for the product you choose. If the wallpaper has not come off yet, our guide on whether to remove wallpaper or paint over it covers that decision first.
Plaster that sounds hollow
Tap the wall with your knuckles or the handle of a screwdriver. Sound plaster gives a dull, solid note. A hollow, drummy sound over an area means the plaster has come away from the brick or block behind, which is known as blown plaster. Cracks across it will keep reopening however well they are filled, because the plaster underneath is moving. The loose section has to be cut back to firm edges and made good. Small patches can be built back up, while larger areas need replastering and then a long drying time before decorating.
Holes left by fixings
Old wall plugs should be pulled out or pushed slightly below the surface. Filling over a plug that sits proud leaves a bump. If you plan to hang something heavy in the same place again, decide that now. A hole that only needs to take paint is filled, but a wall that has to carry a TV or wall cabinets again may need timber support behind the board, which is plasterboard repair work rather than preparation.
Old water stains
A water mark can only be prepared once it is dry and the source has been dealt with. If you are not sure the leak has stopped, our guide on what to do about a water leak at home covers the common sources. Press the stained area firmly. Board that has dried out and still feels hard needs filling where necessary and then a stain-blocking primer, taken a little beyond the edge of the mark, because ordinary emulsion lets water stains bleed through. Board that feels soft, crumbles or has swollen has lost its strength, and our guide on whether to repair or replace damaged drywall explains what usually happens next.
Previous repairs that show
Many walls carry old repairs that were never finished properly: patches that stand proud, filler cracked around its edges, or spots that look dull or shiny under the paint. Loose or cracked filler is cut out and the hole refilled. Patches that stand proud are sanded back until they are flush. Dull or shiny spots, known as flashing, are usually a priming problem rather than a filling one, and a spot-prime before the next coat normally deals with them.
The order of work on a damaged wall
- Fix the cause and let the wall dry. Leaks repaired, ventilation sorted, and damp areas left until they are dry right through.
- Carry out repairs. Popped screws refixed, cracked joints re-taped, holes patched and blown plaster made good. Repairs need their own drying time.
- Clean and remove anything loose. Filler bonds poorly to grease and dust, and flaking paint is scraped back to a firm edge.
- Seal torn paper and very porous patches. This stops the filler and paint from soaking in or lifting the surface.
- Fill in thin layers. Deep holes and wide cracks are built up gradually, with each layer left to harden before the next. Filler that is still soft in the middle will shrink and sink later.
- Sand, check and refill. A second pass of fine filler is normal, as sanding often reveals small hollows that were not visible before.
- Caulk moving joints. Gaps along skirting, door frames and the wall-to-ceiling line are sealed with flexible caulk.
- Stain-block and spot-prime. Water marks get a stain-blocking primer, and filled or bare areas are primed so they take paint at the same rate as the rest of the wall.
This takes longer than most people expect. A wall with deep repairs may need two or three short sessions spread over separate days, because each layer has to dry before the next stage can start. Cold, damp rooms slow everything down.
How to tell the wall is ready
- Run a flat hand over every repair. You should not feel a ridge, a dip or a gritty edge.
- Shine a torch along the wall from the side. Low, raking light shows hollows and ridges that look invisible face-on.
- Check the filler has hardened all the way through. Fully dry filler is hard and even in colour. Darker or softer areas are still drying.
- Treat the first coat as a test. A thinned mist coat or first coat often shows up small flaws that were missed. Fill and spot-prime them then, before the finish coats go on.
If the repaired area is in the middle of a wall, paint the whole wall from corner to corner. Even a perfect repair can show when only a patch is painted, because the surrounding paint has faded and gained a slight sheen over the years.
When to hand it over
Some walls are mostly filling, caulking and priming, just more of it than usual. Voltify Contractors’ wall preparation service can do that as a preparation-only visit if you want to apply the finish coats yourself, or as the first stage of interior painting if the whole room needs decorating. If your list includes holes through plasterboard or board damaged by water, the repair needs doing first. Daylight photos of each wall, with close-ups of the worst areas, give the clearest picture of what is involved.
