How to fill holes and cracks in walls before painting (2026)
Quick Answer
To fill holes and cracks before painting, first make sure the wall is dry, stable and free of loose material. Clean and open the damaged area slightly if needed, apply the right filler for the size and type of defect, let it dry fully, then sand smooth, remove dust and prime before painting. The key is not rushing: filler applied over dust, movement or damp usually fails and shows through the finish.
Overview
A neat paint finish depends as much on surface preparation as on the paint itself. Small nail holes, dents and fine cracks can usually be repaired by a careful DIYer, but the repair only lasts if you deal with the cause as well as the surface. That means checking for damp, crumbling plaster, recurring movement or peeling paint before you reach for filler. If the wall is sound, the basic method is simple: remove anything loose, shape the defect so fresh filler can grip, apply filler in controlled layers, allow it to dry as directed on the product label, sand flush, then seal or prime the repair so the paint dries evenly. Different fillers suit different jobs. Lightweight fillers are handy for small cosmetic holes, whereas deeper repairs often need a tougher powder or ready-mixed interior filler. Flexible decorators’ caulk is usually better than rigid filler where two surfaces meet, such as along skirting boards or around architraves. Taking time over dust removal, drying and priming matters because patched areas otherwise flash, sink, crack or stand proud under paint. If cracks keep returning, are wide, or suggest movement in the building, treat that as a repair issue first and a decorating job second.
Who this is for
Homeowners, tenants allowed to decorate, landlords and DIY beginners repairing minor wall defects indoors before painting.
What you’ll need
- Dust sheets or floor protection
- Scraper or filling knife
- Utility knife for opening cracks carefully if needed
- Suitable wall filler for the defect type and depth
- Decorators’ caulk for gaps at joints and trim if needed
- Fine or medium-fine abrasive paper or sanding sponge
- Soft brush or vacuum for dust removal
- Clean cloth
- Primer, sealer or mist coat as appropriate to the paint system
- Paint and painting tools
- Safety glasses and dust mask if sanding
Before you start
Check that the damage is only cosmetic. Do not simply fill over damp patches, staining, bubbling paint, active leaks, mould, crumbling plaster, or cracks that are widening or returning quickly. Read the filler and paint manufacturer instructions for compatibility, drying time, maximum fill depth and whether priming is required. Test for hidden cables or pipes before cutting into a wall, especially near sockets, switches and plumbing routes.
Step-by-step
- 1
Assess the defect and choose the right filler
Look at the size, depth and location of each hole or crack. Use an interior wall filler for small holes, dents and stable cracks in plaster or drywall. Use a flexible decorators’ caulk where two materials meet or where slight movement is normal, such as along skirting boards, door frames and coving. If the wall is damp, loose or structurally cracked, stop and fix the underlying problem first.
Why: Different repair materials behave differently. Rigid filler can crack at movement joints, and cosmetic repairs will fail if the substrate is unstable or damp.
- 2
Prepare the area properly
Lay dust sheets, scrape away flaking paint, loose plaster and any crumbly filler, then brush or vacuum out dust. For fine cracks, carefully widen the surface slightly into a shallow V-shape with a scraper or knife so the filler can get in, not just bridge the top. For holes, remove any loose edges and undercut fragile rims if needed without enlarging the damage more than necessary.
Why: Filler sticks to solid, clean edges, not dust or loose paint. Opening a crack slightly gives the repair material a key so it is less likely to pop out later.
- 3
Apply filler in controlled passes
Press the filler firmly into the hole or crack with a filling knife so there are no voids behind the surface. Smooth off the excess, leaving the repair just proud of the wall if you plan to sand it back. For deeper holes, build up in layers if the product instructions require it rather than packing in too much at once. If using caulk at joints, apply a neat bead and smooth it with the method recommended by the manufacturer.
Why: Well-packed filler is stronger and less likely to shrink, sink or crack. Layering deep repairs helps them dry and cure properly.
- 4
Let the repair dry fully
Leave the filler until it is fully dry or cured as stated on the packaging before sanding or painting. Keep the room ventilated if the product instructions allow, but avoid forcing the process in a way the manufacturer does not recommend.
Why: Partly dry filler can tear during sanding, clog abrasives and fail under paint. Painting too soon can trap moisture and make the patch visible.
- 5
Sand smooth and check with side light
Sand the repair until it is flush with the surrounding wall. Run your hand over it and look across the surface with light from the side to spot ridges, hollows or knife marks. If needed, apply a second skim, let it dry and sand again.
Why: Paint highlights imperfections, especially with matt daylight or sheen finishes. Side light reveals defects better than looking straight at the wall.
- 6
Remove dust and seal the repair
Brush, vacuum or wipe away all sanding dust. Prime or seal the patched area if the filler manufacturer or paint system calls for it, or if the repair is more porous than the surrounding wall. On new bare plaster patches, use the paint manufacturer’s recommended prep before topcoating.
Why: Dust weakens paint adhesion, and porous repairs can absorb paint unevenly, causing flashing, patchiness or different sheen.
- 7
Paint the wall
Once the repair is sound, smooth, dust-free and properly sealed, apply your chosen paint in line with the paint manufacturer’s instructions. Blend repaired areas carefully, and repaint the whole section or wall if needed for an even finish.
Why: Even a good filler repair can stand out if the paint is applied unevenly or only dabbed onto a visible patch.
Why this works
This process works because durable repairs rely on three things: a stable substrate, mechanical key and compatible finishing. Cleaning and opening the defect improves adhesion, proper filling restores the surface plane, drying prevents shrinkage problems, and sealing equalises porosity so the final paint film dries to a uniform appearance.
Common mistakes to avoid
- Filling over damp, dirty or flaky surfaces
- Using rigid filler in moving joints instead of flexible caulk
- Applying deep filler in one heavy application when the product needs layering
- Sanding before the filler is fully dry
- Skipping dust removal before priming or painting
- Painting straight onto porous filler without sealing when the paint system requires it
- Ignoring recurring cracks that may indicate movement rather than simple surface damage
Troubleshooting
The repair shrinks or sinks after drying
Apply another thin layer once the first is fully dry, then sand smooth. For deeper holes, use a filler suitable for deeper builds and follow the product guidance on layering.
The crack reappears after painting
Rake out the crack again, check for movement or loose plaster, and use the appropriate repair method. If the crack is at a joint or trim, flexible caulk may be more suitable than hard filler.
The patched area flashes or looks dull under paint
Lightly sand if needed, remove dust and apply the recommended primer or sealer to equalise porosity before repainting.
Filler crumbles out of the hole
Remove the failed repair, clean out all dust and loose edges, then refill onto a sound substrate. Check whether the wall is damp or friable.
The surface still looks lumpy after painting
Let the paint dry, sand back the high spots carefully, skim-fill any hollows, then reprime and repaint.
Compare your options
Lightweight ready-mixed filler
Best for: Small nail holes, pinholes and minor dents
Pros: Easy to use, simple for small cosmetic repairs, usually sands easily
Cons: Not always the best choice for larger or deeper repairs and may be less durable in some situations
Powder filler mixed on site
Best for: Larger holes or repairs where a firmer fill is needed
Pros: Can be economical for bigger jobs, often suitable for more substantial patching
Cons: Needs mixing correctly and can be less convenient for tiny repairs
Flexible decorators’ caulk
Best for: Gaps where slight movement is expected, especially around trim and at junctions
Pros: Stays more flexible than standard filler, useful before painting around woodwork
Cons: Not intended for all hole repairs and may not sand the same way as wall filler
| Option | Best for | Pros | Cons |
|---|---|---|---|
| Lightweight ready-mixed filler | Small nail holes, pinholes and minor dents | Easy to use, simple for small cosmetic repairs, usually sands easily | Not always the best choice for larger or deeper repairs and may be less durable in some situations |
| Powder filler mixed on site | Larger holes or repairs where a firmer fill is needed | Can be economical for bigger jobs, often suitable for more substantial patching | Needs mixing correctly and can be less convenient for tiny repairs |
| Flexible decorators’ caulk | Gaps where slight movement is expected, especially around trim and at junctions | Stays more flexible than standard filler, useful before painting around woodwork | Not intended for all hole repairs and may not sand the same way as wall filler |
Alternatives
- Use a mesh or self-adhesive patch system for larger damaged areas if the filler manufacturer recommends it
- Cut out and patch damaged plasterboard where the substrate is broken rather than trying to bridge a large void with filler alone
- Hire a plasterer for widespread cracking, blown plaster or visibly uneven walls
Pro tips
- Use side lighting from a lamp or window to spot defects before you paint
- Keep your filling knife clean to avoid dragging dried bits through fresh filler
- It is usually easier to add a second skim than to sand down a heavy ridge
- Label or keep the filler packaging until the job is done so you can recheck drying and overpainting advice
- If repainting only one area leaves a visible patch, repaint the full wall for a more uniform finish
Safety notes
- Wear eye protection and a suitable dust mask when scraping and sanding
- Take care using knives or scrapers, especially above shoulder height
- Check for hidden electrical cables and pipework before cutting into walls near fittings or service routes
- Ensure good ventilation when using fillers, primers or paints, following the product safety instructions
What this guide does not cover: This guide covers minor interior wall repairs before painting. It does not cover structural cracking diagnosis, asbestos risks in older materials, exterior masonry repairs, major plaster replacement, or specialist fire-rated or moisture-resistant systems.
Cost considerations
Minor filling and sanding is usually a low-cost part of decorating, but repeated cracking, damp-related damage or loose plaster can turn it into a repair job that costs more than the paintwork itself. Buying the right filler for the defect is usually cheaper than redoing a failed repair.
Prefer to hire a professional?
If this job is beyond a confident DIY — or the work needs to be done by a licensed professional — you can find a verified painter or decorator through Trade Directory (tradedirectory.co.nz), New Zealand's directory of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.
Find a painter or decorator on Trade DirectoryFrequently asked questions
Can I paint straight over filler?+
Often you need to let it dry fully first and then seal or prime it if the manufacturer or paint system says so. Bare filler can absorb paint unevenly, leaving a visible patch.
Should I use caulk or filler for cracks?+
Use filler for stable cracks in the wall surface. Use flexible decorators’ caulk where surfaces meet or where slight movement is normal, such as between trim and wall.
Do I need to sand every repair?+
Usually yes if you want an invisible finish. Even smooth-looking filler often leaves slight ridges that show once painted.
Why do cracks keep coming back after I fill them?+
The wall may be moving, the crack may not have been prepared properly, the wrong product may have been used, or there may be damp or loose plaster. Recurrent or widening cracks should be investigated rather than repeatedly covered.
Can I fill over peeling paint?+
No. Remove loose paint first and repair back to a sound surface, otherwise the filler and new paint can fail together.
Sources & references
Guidance on this page is traced to documented sources. Last checked 24 September 2026.
- Dulux Trade · manufacturer
Supports the need for proper surface preparation, removal of loose material, correct priming or sealing, and following paint system instructions for repaired areas.
- Health and Safety Executive · government
Supports safety points on dust control, PPE, and safe handling of decorating materials.
The basic repair method changes little, but exact drying times, overpainting advice and product suitability vary by manufacturer.