Which wall cracks are safe to fill myself?

Only small, dry, shallow cracks that appear stable in an otherwise sound painted interior plaster or plasterboard wall. Cracks that widen, recur, show moisture, shift out of plane or appear with sticking doors or windows need professional assessment before cosmetic repair.

Should I use a flexible or rigid wall filler?

Use a paintable product the manufacturer explicitly approves for the wall material and crack width. Very slight movement may require an appropriate flexible product, while cracks with continuing movement need investigation; rigid filler is not a structural fix.

Why is the filler sinking or cracking again?

Some fillers shrink as they dry, especially if applied too thickly. Let the first coat cure and add a thin second coat only if the product allows. If the actual crack reopens or spreads, stop patching and investigate what is moving or causing moisture.

Can I sand and repaint straight away?

No. Follow the maker's curing time before any finishing or painting. Sand only when the wall finish and filler are known safe to abrade; old coatings may need testing or professional handling. Remove dust, prime where specified and use compatible paint.

Guides/Home/How to Fill a Small Crack in an Interior Wall

How to Fill a Small Crack in an Interior Wall

Repair a narrow, dry, stable cosmetic crack in a painted interior plaster or plasterboard wall using suitable paintable filler. Inspect for warning signs, clean loose edges, fill in thin layers and blend the finish before repainting. Do not use this method for widening, damp, deep or displaced cracks.

If the mark is a small nail hole rather than a crack, use How to Fill Small Nail Holes in a Wall instead.

Updated Nov 12, 2026

45 min8 stepsIntermediatenew

Close-up of a small hairline crack on a dry painted interior wall with a ruler held nearby to assess its width.

AI illustration

Step 01 / 08

Check that the crack is only cosmetic

Examine the full length in good light. Continue only if the crack is narrow, dry, shallow and apparently stable in a sound painted plaster or plasterboard wall. Stop and seek qualified assessment if it is widening, deep, displaced, repeatedly reopening, damp, associated with sticking doors or windows, or runs diagonally from openings. Do not fill a suspected structural or water-damage crack to conceal it.

Guide progress1 / 8

1. Check that the crack is only cosmetic
Instructional illustration generated with AI for Howmigo.
Examine the full length in good light. Continue only if the crack is narrow, dry, shallow and apparently stable in a sound painted plaster or plasterboard wall. Stop and seek qualified assessment if it is widening, deep, displaced, repeatedly reopening, damp, associated with sticking doors or windows, or runs diagonally from openings. Do not fill a suspected structural or water-damage crack to conceal it.
2. Protect the area and check the coating
Instructional illustration generated with AI for Howmigo.
Move objects away and spread a dust sheet. Check the wall's age and finish before scraping or sanding. If old paint may contain lead or the substrate may contain asbestos, do not disturb it; arrange suitable professional assessment. Keep children and pets away from the work area. Wear gloves and follow the filler manufacturer's ventilation and safety directions.
3. Lift loose material without widening the crack
Instructional illustration generated with AI for Howmigo.
On a known-safe modern finish, use the edge of a flexible filling knife to remove only flaking paint or crumbling previous filler that is already loose. Do not gouge sound plaster, enlarge the crack aggressively or cut into an unknown wall. If material keeps crumbling, stop; the repair may need a different method.
4. Brush clean and let the surface dry
Instructional illustration generated with AI for Howmigo.
Gently brush or vacuum loose dust from the crack and surrounding wall. If allowed by the filler instructions, lightly wipe the surface with a barely damp cloth. Let the area dry completely before applying filler; moisture or residue can weaken adhesion. Check again for any water staining or fresh dampness and stop if present.
5. Press suitable filler into the crack
Instructional illustration generated with AI for Howmigo.
Choose a paintable interior filler explicitly rated by its manufacturer for this wall material and crack width. Follow its preparation instructions. With a clean flexible knife, press a modest amount across the crack so it contacts both sides and fills the gap; smooth excess away with a shallow pass. If the product specifies a maximum layer thickness, stay within it. Do not bridge a moving joint with rigid filler.
6. Allow curing and correct any shrinkage
Instructional illustration generated with AI for Howmigo.
Leave the filler undisturbed for the manufacturer's stated drying or curing time, which varies with product, depth, humidity and temperature. Examine the repair in angled light. If it has shrunk or has a small low spot, add another thin coat only as the product permits, then let it cure fully. A crack that reopens or continues moving needs investigation rather than repeated filling.
7. Blend the finish and prepare for paint
Instructional illustration generated with AI for Howmigo.
If the coating and filler are known safe to abrade, gently smooth small ridges with fine abrasive using dust precautions appropriate to the product. Avoid sanding unknown or suspect old finishes. Remove dust with a soft brush or cloth. Apply compatible primer if the filler or paint maker requires it, then touch up with matching paint once the area is ready; let each coating dry as directed.
8. Inspect the painted repair after drying
Instructional illustration generated with AI for Howmigo.
Once paint has dried according to its instructions, look along the wall under side lighting. The surface should be smooth, dry and evenly coated, with no raised edges or fresh cracking. Minor colour differences may require a wider touch-up rather than more filler. If the crack returns, grows or shows moisture, stop cosmetic repairs and investigate the cause.