How To Fill Gaps Between Skirting Boards and Floorboards

What is the best product to fill 3–10mm gaps between skirting boards and floorboards?

Selleys No More Gaps is the product for this job. It gives a long lasting, paintable finish for gaps inside the home, and its water-based formulation delivers the flexibility and long-term resistance to cracking and crumbling that a skirting joint needs.

The size range in your question is the important part, and it happens to land right on the product limit. The No More Gaps Interior Multipurpose data sheet specifies a maximum gap of 10mm wide by 5mm deep. A 3mm gap is comfortably within that. A 10mm gap is at the edge of it — fillable, but only if you keep the depth to 5mm rather than packing the filler all the way back into the void.

Why the depth limit matters more than the width

This is the single most useful thing to understand about a water-based gap filler. It is water-based, so as it dries it loses that water and shrinks slightly. The deeper the bead, the more total shrinkage there is, and shrinkage is what cracks the paint film sitting over the top. Selleys is explicit that the 10mm × 5mm limit exists to minimise the effects of shrinkage and the paint cracking that follows.

So for a wide gap, resist the urge to fill it in one go. Fill to about 5mm of depth, let it dry, and add a second pass if the joint is still hollow. You will get a better result than a single deep bead, and the paint over it will survive.

The published figures

Technology	Water-based acrylic
Colour	White
Density	1.64
Skin time	Approximately 20 minutes (23°C, 50% RH)
Cure to touch	30 minutes before painting or sanding
Full cure	24 hours
Movement capability	Up to 15% (ISO 9046)
Elongation at break	+300% (ASTM D412)
Maximum gap	10mm wide × 5mm deep
Shelf life, unopened	24 months

Indicative data only, not intended for the preparation of specifications.

Paint-over times, by paint type

This is the detail that most often decides whether the finished joint looks right. The filler has to have skinned before paint goes on, and different paints need very different waits:

Semi-gloss	0 minutes
Gloss	10 minutes
Low sheen	10 minutes
Flat	100 minutes
Ceiling	120 minutes

Flat and ceiling paints need the extra time because they are highly filled and contain less binder than a gloss, so the dried film flexes less and is far more likely to craze as the sealant underneath finishes drying. For oil-based paints, allow 24 to 48 hours.

How to fill the joint

1. Vacuum the gap and wipe the skirting and floor either side. The surface has to be clean, dry and free of dust or grease.
2. Cut the nozzle at a 45° angle to roughly the width of the gap, fit it to the cartridge, and load a caulking gun.
3. Apply by pushing the product into the gap, working in one continuous run rather than short stabs.
4. Smooth off with a wet gloved finger or a spatula, leaving enough product in the joint.
5. Clean up excess with a damp cloth immediately, before it dries.
6. Let it skin — about 20 minutes — then paint according to the times above.

Apply above 10°C. Below that the product will not dry or perform properly.

Limitations

• Not suitable for permanent water immersion or constantly damp areas. In a bathroom or laundry, the gap around a bath or sink needs Wet Area Silicone instead.
• Not suitable for gaps between tongue and groove boards or weatherboards. Use No More Gaps Exterior for those.
• Not suitable for polyethylene, polypropylene or Teflon.
• Movement capability is up to 15% — enough for a skirting joint, but not for a joint that moves a great deal. Where movement is excessive, a silicone sealant is the right answer.

If you would rather see timber than paint

No More Gaps is white and made to be painted. If the skirting and the floor are both finished timber and you do not want a painted line, No More Gaps Timber Flooring comes in four timber-matched colours — Jarrah, Hardwood, Walnut and Baltic — in 380g cartridges, contains real wood fibre, and is both sandable and stainable. Its listed uses include skirting boards and architraves. Allow at least 24 hours before sanding residue off the timber, and note that it is not for gaps wider than 3mm in trafficable joints and not for exterior use.

Common questions

Can I fill a 10mm gap in one pass?

Only if you keep it to 5mm deep. The 10mm limit is on width; the 5mm limit is on depth, and it is the depth that drives shrinkage and paint cracking.

How soon can I paint?

Semi-gloss immediately after skinning, gloss and low sheen at 10 minutes, flat at 100 minutes, ceiling paint at 120 minutes. Oil-based paints need 24 to 48 hours.

How long until it is fully cured?

24 hours for full cure. It is dry to touch and ready to paint or sand at about 30 minutes.

Can I sand it?

Yes, once it has cured to touch at around 30 minutes.

How much movement will it handle?

Up to 15% under ISO 9046.

What if the room is cold?

Apply above 10°C. Cold or humid conditions extend drying times.

How do I clean up?

Damp cloth, immediately, while the product is wet. Cured product has to be scraped off.

Can I use it in a bathroom?

Not for constantly damp areas or anywhere subject to water immersion. No More Gaps Bathroom & Kitchen is formulated for damp rooms, but even that product directs you to Wet Area Silicone for gaps around baths, sinks and showers.

Is there a step-by-step guide?

Yes — how to fill gaps between skirting boards and walls, and how to update skirting boards if you are refinishing the whole run.