How To Fill Cracks and Dents in Walls
How do you fill cracks and dents in walls?
Hairline cracks around doors and windows, holes left by old picture nails, and dents from furniture or a stray elbow are ordinary wear on a painted wall. Fixing them is one of the easiest jobs in the house: clean the surface, press Selleys Spakfilla Rapid firmly into the defect, scrape off the excess, let it dry, sand lightly and paint.
The detail that decides how long you wait is not the size of the crack across the wall but how deep the fill is. Spakfilla Rapid's technical data sheet gives two very different figures: less than 2 mm dries in 30 minutes, more than 2 mm needs 24 hours. Most picture-hook holes and hairline cracks fall into the first category, which is why this is genuinely a same-afternoon job. A deeper dent does not.
Technical specification
| Technology | Water based |
| Appearance | Smooth paste |
| Colour | White |
| Sand / paint time — less than 2 mm | 30 minutes |
| Sand / paint time — more than 2 mm | 24 hours |
| Shrinkage | Virtually non-shrinking |
| Use | Interior and exterior |
| Pack sizes | 180 g and 260 g tubs |
Indicative data only, not intended for the preparation of specifications.
What "virtually non-shrinking" changes about how you work
Most people learn to overfill a repair because the filler they grew up with sank as it dried. Spakfilla Rapid is described as virtually non-shrinking and non-cracking, and Selleys' direction is explicit: there is no need to overfill. That single fact changes the technique. Instead of mounding filler above the surface and sanding a crater back flat, you press it in, take the excess straight off with the blade, and sand only lightly. Less filler on the wall means less dust in the air and far less chance of sanding through the surrounding paint.
The other useful figure is that it needs only one application. For anything under 2 mm you fill once, wait half an hour and paint. That is what makes it worth keeping a tub in the house rather than buying filler each time something gets knocked.
What you need
- Selleys Spakfilla Rapid
- A filling blade or scraper
- Fine sandpaper
- A dust pan and broom, or a cloth
- Selleys Sugar Soap or Selleys Super Kleen for cleaning dust off before painting
- Undercoat and your topcoat
How to fill cracks and dents
- Prepare the surface. Make sure it is clean, dry and free of loose or powdery material. Sand lightly first if there is anything protruding.
- Press the filler in. Use a filling blade or scraper to firmly press Spakfilla Rapid into the crack, dent or hole. Pressing rather than smearing is what gets filler to the back of the defect, where it grips.
- Scrape off the excess and feather the edge. Take the surplus off to minimise sanding, and feather the edge so it merges with the wall. A feathered edge is what makes a repair disappear under paint; a hard-edged patch catches the light no matter how well you paint it.
- Let it dry. 30 minutes for fills under 2 mm; 24 hours for anything deeper. Expect longer again in cold or humid conditions.
- Sand lightly. Fine sandpaper, and only lightly — minimal sanding is required for a smooth finish.
- Clean off the dust. Before painting, clean dust and loose filler particles off using Selleys Sugar Soap or Selleys Super Kleen.
- Undercoat, then paint. For best results apply an undercoat before your topcoat. For oil-based paints, allow 24 hours before painting.
Limitations — where Spakfilla Rapid should not be used
The technical data sheet is specific about this, and the limits are easy to run into around a house.
- Not on plastic or metal, and not on exterior timber likely to swell or shrink as it absorbs water.
- Not below 5°C or in wet conditions.
- Do not nail it. A filled hole is not a fixing point.
- Not where load or compression occurs, as the product may be crushed. Selleys' own example is the spot behind a door where the knob strikes the wall — fill it and it will be crushed out again the next time the door swings hard.
- Where movement occurs, use Selleys No More Gaps instead. A crack that keeps reopening is a moving joint, and a rigid filler will keep splitting along it.
That last point covers most repeat failures. Hairline cracks in the middle of a sheet of plasterboard are a filling job. Cracks that follow the line where two materials meet — plaster to timber, wall to cornice — usually are not.
Clean up and storage
Uncured filler comes off with water, and your application tools can be cleaned with water. Cured filler has to be scraped or sanded off. Keep the container closed when not in use. If the filler has stiffened in the tub, stir it; if it is still too dry, add a teaspoon of water and stir again to the consistency you want. Product that has properly hardened should be discarded.
Safety: what the products in this job are classified for
| Product | Classification |
|---|---|
| Spakfilla Rapid | Warning — H317 may cause an allergic skin reaction; H319 causes serious eye irritation |
| Sugar Soap (concentrate) | Danger — H318 causes serious eye damage |
| Super Kleen | Warning — H315 causes skin irritation; H319 causes serious eye irritation |
The H317 on the filler is about step 2, and about doing this job often. Skin sensitisation is not irritation. It is the immune system learning to react to the material; once that has happened it is generally permanent, and thereafter far smaller exposures than the one that caused it will provoke a reaction. The method above already tells you to press the filler in with a blade or scraper rather than a finger, and that is the technique that keeps the repair flat. It also happens to be the thing that stops a tub of filler a year, over years of picture hooks and door dings, turning into a sensitisation.
The H318 belongs to the bottle, not the bucket. Half a cup in five litres is a weak solution. The two moments that put you in contact with undiluted concentrate are measuring and pouring it, and neat application on a sponge for stubborn marks. Wear eye protection for both. Step 6 of this job also frequently means cleaning dust off a whole wall or a ceiling with a wet cloth above your head, which is the geometry that puts cleaner in an upturned eye — worth goggles even though the solution in the bucket is dilute.
If you only need to lift sanding dust, Super Kleen is the milder option of the two named in step 6. Its classification is eye irritation (H319) rather than eye damage (H318). Sugar Soap is the one to keep for greasy, smoke-stained or heavily marked walls where you actually need the alkali.
An H318 splash needs fifteen minutes of irrigation with the eyelids held open and urgent medical attention. Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.
Common questions about filling cracks and dents in walls
How long before I can paint?
30 minutes for a fill less than 2 mm deep, with water-based paint. Deeper than 2 mm, allow 24 hours. For oil-based paints, allow 24 hours regardless.
Do I need to overfill?
No. Spakfilla Rapid is virtually non-shrinking, so Selleys specifically says there is no need to overfill.
Why has my repair cracked again?
Most likely the crack is a moving joint rather than a static defect. Where movement occurs, Selleys directs you to No More Gaps rather than a rigid filler.
Can I use it outside?
Yes, it is rated for interior and exterior use. In exterior applications, protect the repair from rain until it is dry and painted over with two coats of paint.
Can I fill a hole and then hang a picture on it?
No. The data sheet says do not nail the product, and it should not be used where load or compression occurs.
Will it work on a wooden door or a plaster ceiling?
It is suitable for wallboard, wood, masonry, plaster, primed nail heads and plasterboard. It is not for plastic or metal.
Does humidity really make a difference?
Yes — expect longer drying times in cold or humid conditions. If the room is cold and damp, give it more than the stated time before you sand.
What is the best way to get an invisible repair?
Feather the edge of the fill so it merges with the wall, sand lightly, clean the dust off with Sugar Soap or Super Kleen, then undercoat before the topcoat. The undercoat evens out the difference in porosity between the filler and the old paint.
The paint looks a different colour over the filler.
Some paints may temporarily discolour when applied over the filler, but they revert to the correct colour once dry.
My tub has gone stiff. Can I save it?
Stir it. If it is still too dry, add one teaspoon of water and stir again. Discard filler that has actually hardened.
What about a hole bigger than a dent?
For a substantial hole, see how to repair a large hole in a wall, which uses a mesh patch under the filler.
What product does Selleys recommend for filling cracks and dents in walls according to this guide?
Selleys recommends Selleys Spakfilla Rapid for filling cracks, dents, and holes in walls.
What tools are needed to fill cracks and dents in walls?
You need a scraper, a dust pan and broom or cloth, sandpaper, and a cloth to fill cracks and dents in walls.
What is the first step before filling a crack or dent in a wall?
Make sure the surface is clean, dry and free of loose or powdery material before starting.
How do you apply Selleys Spakfilla Rapid into a crack or dent?
Use a filling blade or scraper to firmly press Selleys Spakfilla Rapid into the crack, dent or hole.
How should excess filler be handled after application?
Scrape off excess filler to minimise sanding, and for a perfect finish, feather the edge to merge with the wall.
How long does Selleys Spakfilla Rapid take to dry?
It takes 2 to 3 hours to dry, depending on humidity.
What should you do after the filler has dried?
Sand the filled area lightly with fine sandpaper after it has dried.
What should be done before painting over the filled area for best results?
For best results, apply an undercoat before painting with topcoat.
How long does the whole process of filling cracks and dents in walls take according to the guide?
The total time for the process is listed as 120 minutes (2 hours).
What causes cracks and dents in walls, according to the page?
Hairline cracks around doors and windows, holes from old picture nails, and dents from bumping furniture (or clumsy teens) are simply part of the wear and tear of life.