How To Fill Gaps Between Skirting Boards and Walls
How do you fill the gap between a skirting board and the wall?
That thin dark line where the skirting meets the wall is what stops a freshly painted room looking finished. Closing it is genuinely simple, even if you have never held a caulking gun: clean the joint, fit the cartridge, run the gun along the gap at about 45° with even pressure, wipe the bead smooth with a damp finger, and clean up immediately.
The product for the job is Selleys No More Gaps Interior Multipurpose. The reason a flexible gap filler is used here rather than a rigid wall filler is worth understanding, because it is the difference between a joint that stays closed and one that splits open again by the following summer. The skirting board and the wall are two different materials fixed to a building that moves. A rigid filler cannot follow that movement; a flexible one can.
Technical specification
| Technology | Water-based |
| Skin time | 20 minutes (23°C, 50% RH) |
| Movement capability | Up to 15% |
| Maximum gap for paint crack resistance | 10 mm wide × 5 mm deep |
| Paintable | Yes; allow 24 hours before oil-based paints |
| Water resistance | Low |
| Suitable for | Interior use |
Indicative data only, not intended for the preparation of specifications.
What you need
- Selleys No More Gaps Interior Multipurpose
- A caulking gun
- Secateurs or a sharp knife
- A cloth for cleaning, and a bowl of water
- Masking tape, if you want the tidiest possible finish
How to fill the gap
- Clean the area. The joint has to be free of dust, grease and loose or flaking paint. Skirting boards collect a surprising amount of both, and a bead laid over dust is bonded to dust.
- Cut the seal and the nozzle. Cut the seal on the No More Gaps cartridge and cut the nozzle with secateurs, then fit the nozzle to the cartridge. Cut the opening to roughly the width of the gap — you can widen it later, but you cannot narrow it.
- Load the gun. Place the cartridge into the caulking gun.
- Run the bead. Position the gun at 45 degrees and apply even pressure to the trigger as you move along the gap. Work in one continuous pass along each wall rather than stopping and starting — joins in a bead are weak points and they show under paint.
- Tool the bead. Use a damp finger or a rounded spatula to wipe off the excess and leave a clean, smooth finish. Do this while the product is still wet; the skin time is 20 minutes, and once it starts to skin, tooling tears the surface instead of smoothing it.
- Clean up. Wipe up with a damp cloth immediately.
When can you paint over it?
Allow the bead to skin before painting — about 20 minutes for water-based paints. Allow longer, around 2 hours, when painting with flat or ceiling paints, or in cooler conditions. Allow 24 hours before painting with oil-based paints.
The reason flat and ceiling paints need so much longer is not obvious, and it is genuinely useful to know. Selleys' data for its No More Gaps Interior Fast Dry variant sets out paint-over times by paint type — 10 minutes for gloss, 100 minutes for flat and 120 minutes for ceiling paint — and explains why: flat and ceiling paints are highly filled, meaning they contain a lower proportion of binder than other paints. A highly filled paint film does not flex as much as the sealant continues to dry underneath it, so it cracks. Give the bead longer under a flat paint and the film has less shrinkage left to cope with.
The other rule that prevents paint cracking is gap size. For optimum paint crack resistance, filled gaps should not exceed 10 mm wide and 5 mm deep. In a bigger gap the effects of shrinkage are more evident, and a thicker bead moves more under the paint film. Avoid applying the paint too thickly over the bead as well.
Getting a clean line
For a neater finish and easier clean-up, tape both sides of the gap before applying the product, then pull the tape while the bead is still wet. This is the difference between a caulk line that reads as part of the joinery and one that reads as a repair, and it takes only a few minutes on a straight run of skirting.
The 45° gun angle in step 4 is not arbitrary either. Held at that angle with the nozzle cut to match, the gun pushes product ahead of the tip and into the gap rather than dragging it across the surface. A bead that has been pushed into the joint has depth of bond on both faces; one laid on top has almost none.
Limitations — where this product should not be used
- Interior only. No More Gaps Interior Multipurpose is not recommended for exterior use or areas exposed to constant water. Outside, use No More Gaps Exterior.
- Low water resistance — not for permanent water immersion or constantly damp areas. Where the joint sees frequent water, an appropriate Selleys silicone sealant is the right product.
- Not suitable for polyethylene, polypropylene or Teflon.
- Not for gaps between tongue-and-groove boards or weatherboards — use No More Gaps Exterior for those.
- Maximum 10 mm wide by 5 mm deep for optimum paint crack resistance.
A gap wider than that behind a skirting board is usually a sign the board is not sitting against the wall. Fixing the board is a better answer than filling the void; if the cavity is genuinely large, Selleys No More Big Gaps expanding foam is formulated for cavities behind skirting boards and architraves, and can be cut back, sanded, plastered or painted once cured.
Clean up
Uncured product wipes off with a damp cloth. Once cured it has to be cut out, and any remaining residue can be softened with acetone before removal — which is a strong argument for wiping as you go rather than at the end of the room.
Safety: the caulk is unclassified, the foam is the opposite
No More Gaps Interior Multipurpose, the product this method is built on, is not classified as hazardous under Safe Work Australia GHS 7 — no signal word, no hazard statements. Two of the alternatives named above do carry one: Interior Fast Dry and Exterior are each Warning — H317, may cause an allergic skin reaction. Wet-finger bead smoothing along a whole room of skirting, repeated over years, is the contact pattern that builds a sensitisation, so tool the bead or wear a glove with those two.
The expanding foam suggested for a genuinely large cavity is a different product entirely. Selleys No More Big Gaps is an isocyanate-based polyurethane foam classified Danger, and it carries the longest hazard list of anything in the range:
| H222 | extremely flammable aerosol |
| H229 | pressurised container, may burst if heated |
| H334 | may cause allergy or asthma symptoms or breathing difficulties if inhaled |
| H351 | suspected of causing cancer |
| H372 | causes damage to organs through prolonged or repeated exposure |
| H362 | may cause harm to breast-fed children |
It also carries H332, H335, H315, H317 and H319.
H334 is the one to understand, and this job is the worst case for it. Respiratory sensitisation works like a skin allergy but in the airways: the immune system learns to react to isocyanate vapour, the change is generally permanent, and afterwards a concentration far below the one that caused it is enough to provoke wheeze or an asthma attack. The exposure window is while the foam expands and cures, not afterwards — and a cavity behind a skirting board is a small, unventilated void at floor level with your face a foot away from the nozzle. That is the geometry the classification is describing.
If the cavity really needs foam: open the room up and ventilate actively rather than opening a door, wear an organic vapour respirator rather than a dust mask, wear nitrile gloves and eye protection, and keep children and anyone with asthma out until it has cured and the room has been aired. H362 means anyone breastfeeding should not use this product. H222 means no heater, no pilot light and no smoking in the room while you dispense — and a skirting-level gas heater is exactly where the propellant will collect.
The lower-hazard answer is usually the one this page already gives: fix the loose board back to the wall, then caulk the remaining gap with the unclassified interior filler. Foam is for a cavity, not for a gap.
Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.
Common questions about filling gaps between skirting boards and walls
How soon can I paint?
Allow the bead to skin, about 20 minutes, for water-based paints. Allow about 2 hours for flat or ceiling paints or in cooler conditions, and 24 hours for oil-based paints.
Why does my caulk line crack after painting?
Usually one of three things: the gap was wider or deeper than the 10 mm by 5 mm limit, the paint went on too thick, or a flat or ceiling paint was applied before the bead had dried enough. Flat paints are highly filled and do not flex with the drying sealant.
How do I get a straight, clean line?
Tape both sides of the gap before applying, tool the bead with a damp finger or rounded spatula, and pull the tape while the product is still wet.
Should I use a filler instead?
No. This joint moves, and Selleys' rigid wall fillers all direct you to No More Gaps where movement occurs. A rigid filler will crack along the same line.
What angle should I hold the gun at?
About 45 degrees, moving steadily along the gap with even trigger pressure so the product is forced into the joint.
How big a gap can I fill?
Up to 10 mm wide and 5 mm deep for optimum paint crack resistance. Anything much larger needs the board refitted, or an expanding foam.
Can I use this in a bathroom?
Not where it will see frequent water. The product has low water resistance; use an appropriate Selleys silicone sealant in wet areas.
How do I clean up excess?
A damp cloth, immediately. Cured product has to be cut out.
Is there a faster-drying option?
Yes — No More Gaps Interior Fast Dry has a skin time of 6 minutes and is paintable in 10 minutes with gloss, semi-gloss or low-sheen paints, though flat and ceiling paints still need 100 and 120 minutes respectively.
Can I get a coloured filler so I do not have to paint?
Selleys makes No More Gaps Coloured Gaps for joints where a colour match is wanted rather than paint.
Do I need to remove the old caulk first?
Yes, along with any loose or flaking paint. The bead only holds as well as the surface underneath it.
What if I am also refitting the skirting boards?
Fix the boards first and caulk last — see how to update skirting boards.
What supplies are needed to fill gaps between skirting boards and walls, according to Selleys?
According to Selleys, you need Selleys No More Gaps Multipurpose, a Selleys Light Speed Caulking Gun, and a cloth for cleaning.
How long does the Selleys guide say the skirting board gap-filling task takes?
The Selleys guide indicates the task takes a total time of 120 minutes (PT120M).
What is the first step in filling gaps between skirting boards and walls?
The first step is to clean the area.
How do you prepare the Selleys No More Gaps cartridge before use?
Cut the seal and nozzle of the Selleys No More Gaps cartridge with secateurs at a 45-degree angle and fit it to the cartridge, then place the cartridge into the Selleys Light Speed Caulking Gun.
At what angle should the caulking gun be held when applying the filler?
The caulking gun should be positioned at 45 degrees while applying even pressure to the trigger as you move it along the gap.
How do you achieve a smooth, clean finish after applying the gap filler?
Use a damp finger or a rounded spatula to wipe off the excess product, ensuring a clean, smooth finish.
What should you do immediately after finishing the application?
Clean up with a damp cloth immediately after finishing the application.
Which Selleys No More Gaps product is recommended for interior gap-filling and what are its features?
Selleys No More Gaps Interior Multipurpose is recommended for interior applications. It is a water-based gap filler in a 475g white cartridge with long-lasting durability, crack resistance, paintability, flexibility, and low shrinkage, and is suitable for plasterboard, wood, particleboard, cement sheeting, aluminium, and glass surfaces.
Is there a faster-drying alternative for filling gaps around skirting boards?
Yes, Selleys No More Gaps Interior Fast Dry can be painted in just 10 minutes. It comes in a 475g white cartridge, is water-based with an advanced skinning formulation, and is ideal for maintenance repairs, emergency repairs, and new builds.
What product should be used for gap-filling in moisture-prone areas like kitchens and bathrooms?
Selleys No More Gaps Bathroom & Kitchen should be used, as it offers superior water and mould resistance with a fungicide to protect against mould growth.