Best Gap Fillers for Every Room in Your Home

Which is the best gap filler to use, and how do you choose between them?

There is no single best gap filler — there is a best one for the location. Selleys' own recommendations split four ways: interior, high-moisture areas, timber floors, and exterior, with a fifth product for brick and cement. Getting this right is what determines whether the repair is still invisible in two years or has reopened by next winter.

The reasoning underneath the split is straightforward. Interior joints move a little as the building expands and contracts, so the filler must flex. Wet areas add mould as a failure mode. Timber floors move a lot with humidity, and the filler has to look like timber. Exterior joints add UV, rain and much larger temperature swings. A product optimised for one of those is compromised in the others.

Interior gaps

If you are repairing a crack or gap inside the house, Selleys recommends a long-lasting filler with flexibility. Fillers used internally should be resistant to further cracking where movement may occur — which is precisely what happens at the joint between two building elements.

For gaps between skirting boards, cornices, or between the wall and ceiling, the two products are No More Gaps Interior Multipurpose and No More Gaps Interior Fast Dry.

The difference between them is how soon you can paint:

	Interior Multipurpose	Interior Fast Dry
Gloss paint	60 minutes	10 minutes
Semi-gloss paint	60 minutes (sheen)	0 minutes
Low sheen paint	60 minutes	10 minutes
Flat paint	180 minutes	100 minutes
Ceiling paint	180 minutes	120 minutes
Maximum gap	10mm wide, 5mm deep	10mm wide, 5mm deep

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

What that means in practice: if you are caulking a room and painting it the same day, Fast Dry saves you most of an afternoon of waiting — the gloss and low sheen figures drop from an hour to ten minutes. If you are caulking today and painting next weekend, the difference is irrelevant and Interior Multipurpose's low shrink and flexibility are what you are buying.

Note that flat and ceiling paints take longest on both products. That is not a quirk — those paints contain less binder and are therefore less flexible, so the filler underneath needs to be further through its cure before you cover it, or the paint film cracks.

High-moisture areas — bathroom, laundry, kitchen

In areas that stay damp for prolonged periods, the filler needs three properties at once: resilient, mould resistant and paintable. Selleys No More Gaps Bathroom & Kitchen is the product, and it is designed for filling and sealing cracks near windows, cabinets, skirting boards and walls. Its joint movement capability is ±25%, and it is paintable after 60 minutes for gloss, sheen and low sheen paints, or 180 minutes for flat and ceiling paints.

Its important limit: No More Gaps Bathroom & Kitchen is not recommended for use around bathtubs, showers and sinks. Those need a waterproof seal, which means a wet area silicone such as Selleys Wet Area Silicone or Selleys No Mould. It is also not for outdoor use or constant moisture exposure, and not for polyethylene, polypropylene or Teflon.

The distinction matters. "Bathroom and kitchen" describes the room, not the joint. Filling the gap where a skirting board meets a tiled laundry wall is the intended use; sealing where a bath meets a wall is not.

Timber floors

Selleys No More Gaps Timber Floors is formulated specifically to seal gaps in timber flooring. It contains wood fibres that give a timber-look finish, and it can be stained to suit your home. It also works for sealing between timber panels and other fittings — kitchen cabinetry, for example.

Its movement capability is 25% (ISO 9046), which it needs: hardwood floorboards move noticeably with temperature and humidity, and that movement is why an ordinary filler fails in a floor.

Limits: not for exterior use; not for gaps larger than 3mm wide in trafficable joints — that is, anywhere people walk; and not for gaps between tongue and groove boards or weatherboards, where No More Gaps Exterior is the right choice. Store above 5°C.

Exterior

Exterior gap filler goes between windows and walls, on the eaves of your home, on paving, fences, tiles, and between particle board and fibre sheeting. If you are filling or sealing anything on the outside of the house, use a product specifically formulated to provide a weatherproof seal — the Selleys exterior range is designed to be weather, mould and UV resistant.

No More Gaps Exterior gives ±25% movement capability (ISO 9046) and is paintable once it has skinned, at roughly 30 minutes. For oil-based paints, allow 24 to 48 hours before painting for best results.

Limits: not for sealing around bathtubs and kitchen sinks; maximum gap 10mm wide by 5mm deep; not suitable for areas prone to frequent water immersion — where excessive joint movement or frequent water contact occurs, use an appropriate Selleys silicone sealant instead; and not to be stored or applied below 10°C. That last figure rules out early winter mornings in much of southern Australia.

Brick and cement

Selleys No More Gaps Bricks & Mortar provides a mortar-like finish appropriate for repairs in brick and cement, pathways, or between brick and the roof. It is paintable, and for best results apply an undercoat before the top coat.

Limits: not for areas of frequent water immersion, not for replacing mortar in construction, and not for moving cracks. Not to be stored or applied below 5°C.

The "not for moving cracks" limit deserves emphasis. A crack in brickwork that is still opening is a structural symptom, and filling it will hide the evidence without fixing the cause. Get the cause diagnosed first.

How to apply gap filler with a caulking gun

The technique is the same whichever product you choose.

1. Understand the gun. A caulking gun has a barrel or cradle that holds the cartridge, a plunger rod, a large trigger for extruding product, and a small trigger that releases the plunger rod so you can remove the cartridge.
2. Prepare the cartridge. Cut the tip off the cartridge — secateurs work well for this and are safer than a knife. Cut the nozzle to the width of the joint or the bead size you want, at a 45 degree angle. Insert the cartridge into the gun, making sure the plunger rod is pulled all the way out first.
3. Practise, then apply. If it is your first time, gun some product onto cardboard to get a feel for how it comes out. Then apply into the joint, gunning in a forwards direction and making sure the product is pushed in as you go. When you release the trigger to pull again you may get a small blob — that smooths out when you tool the bead.
4. Finish the joint. Soapy water often works well for smoothing, though the manufacturer of the product will recommend the best way to finish their own sealants and fillers.

The step that most affects durability is pushing the product into the joint rather than laying it on the surface. A bead sitting on top has almost no depth of bond and will peel away; one pressed into the gap grips both faces and can flex with them.

Common questions about choosing a gap filler

What is the best gap filler for skirting boards?

No More Gaps Interior Multipurpose or Interior Fast Dry. Both are flexible enough to resist further cracking where movement occurs, which is what a skirting board joint does.

Which gap filler dries fastest?

Interior Fast Dry. Semi-gloss paint can go on immediately, gloss and low sheen at 10 minutes, against 60 minutes for the Multipurpose version.

Can I use No More Gaps Bathroom & Kitchen around the bath?

No. It is not recommended around bathtubs, showers and sinks — use a wet area silicone sealant there instead.

What is the biggest gap these products will fill?

10mm wide by 5mm deep for the interior products and for No More Gaps Exterior. Larger than that and shrinkage during cure becomes visible.

Can I fill gaps between floorboards?

Yes, with No More Gaps Timber Floors — but not gaps larger than 3mm wide in trafficable joints, and not between tongue and groove boards.

Can I stain gap filler to match my floor?

No More Gaps Timber Floors contains wood fibres for a timber-look finish and can be stained. It can also be varnished or painted once dry.

Why does the paint crack over my filled gap?

Usually the gap was over the 10mm × 5mm maximum, so shrinkage during cure was more pronounced, or a low binder paint went on before the filler had cured enough. Flat and ceiling paints are the ones most prone to this.

What temperature is too cold to apply gap filler?

No More Gaps Exterior should not be stored or applied below 10°C. Bricks & Mortar and Timber Floors have a 5°C floor.

How do I cut the nozzle?

To the width of the joint or the bead size you want, at a 45 degree angle. Secateurs are safer than a knife. Cut smaller than you think — you can always widen the opening, but you cannot make it smaller again.

Is exterior gap filler UV resistant?

The Selleys exterior range is designed to be weather, mould and UV resistant. Interior products are not, which is the main reason not to substitute one for the other.