What is Selleys No More Cracks Exterior Wood Filler, and where should you use it?

Selleys No More Cracks Exterior Wood Filler is a ready to use, weather resistant flexible filler for exterior timber. It is a pine coloured paste that flexes with the timber's natural movement, so it will not crack, split or fall out of the repair the way a rigid filler can when the boards around it swell and shrink through the seasons.

Two practical points sit behind that. First, it is stainable and paintable, so the repair can be finished either way — you are not locked into paint. Second, priming is unnecessary before filling, which removes a step compared with fillers that specify a primed exterior substrate. You still protect the repair from rain until it is painted.

What the key numbers mean in practice

• 2–3 mm application: 2–3 hours to dry at 25°C
• 10 mm application: 16 hours or more
• 450 g tub

Those two drying figures are the most useful numbers on the page, because the relationship between them is not proportional. Going from a 3 mm fill to a 10 mm fill roughly triples the depth but multiplies the drying time by five or six. Depth costs disproportionately, which is exactly why Selleys directs you to apply deeper repairs in 10 mm layers rather than in one pass.

Plan the job around that. A morning of shallow fills on window frames and trim can be sanded and painted the same afternoon. A deep repair to a rotten section is an overnight job at minimum, and a very deep one is a multi-day sequence of layers.

Note that these are 25°C figures. In cooler conditions expect longer — and the product is not to be used below 5°C at all.

Where to use it

It is suitable for all exterior timber — window frames, doors, trim, weatherboards, decking components and similar external joinery, wherever a hole, split or damaged section needs to be made good and then painted or stained.

The pine colour is a starting point rather than a match. Selleys makes one specific point about staining: when tinting or staining, the final colour is not achieved until the varnish is applied. If you are colour matching a stained finish, judge the match after varnishing, not before — a stained repair that looks slightly off before the varnish goes on will very likely look different again afterwards.

For interior timber, use No More Cracks Interior Wood Filler instead; the full range is on the wall filler page. Selleys also has advice on splits in wood.

How to apply it

1. Make sure the surface is clean and dry.
2. Remove rotten wood and fix splits before filling. This is the step that decides whether the repair lasts. Filler placed over rot hides the problem rather than stopping it, and the rot continues underneath.
3. Press the filler firmly into the surface and remove the excess. Removing excess now saves sanding later.
4. For deeper repairs, apply in 10 mm layers, letting each layer dry.
5. Allow it to dry — 2–3 hours for a 2–3 mm application at 25°C, 16 hours or more at 10 mm.
6. Sand, then paint or stain. It can also be nailed or planed.
7. Protect the repair from rain until it has been painted.
8. Clean tools with water before the filler dries.

Limitations — where Exterior Wood Filler should not be used

These are the manufacturer's stated limits:

• Not for permanently wet areas. Weather resistant is not the same as immersed or constantly damp.
• Not for joints subject to movement. This one needs reading carefully alongside the product's flexibility claim. The filler flexes with the natural movement of the timber it is filling; that is different from bridging a joint between two components that move relative to each other. For a joint that moves, use a flexible gap filler such as the Selleys No More Gaps range instead.
• Do not use below 5°C.
• Protect from rain until painted. Until the paint or stain system is on, the repair is exposed.

Hazard classification

Classified as hazardous under Safe Work Australia GHS 7, with the signal word Warning.

• Sensitisation — Skin — Category 1. H317: may cause an allergic skin reaction.

It is not classified as Dangerous Goods under the Australian Code for the Transport of Dangerous Goods by Road & Rail or New Zealand NZS5433.

What is in it

Chemical entity	CAS number	Proportion (w/w)
Poly[oxy(methyl-1,2-ethanediyl)], alpha-(methylphenyl)-omega-hydroxy-	9064-13-5	<1%
1,2-Benzisothiazol-3(2H)-one (BIT)	2634-33-5	<0.05%
2-Methyl-1,2-benzisothiazol-3(2H)-one (MBIT)	2527-66-4	<0.05%
2-Octyl-2H-isothiazol-3-one (OIT)	26530-20-1	<0.05%
Ingredients determined to be non-hazardous or below reporting limits	—	Balance

The striking thing about that table is how little of the product is classified at all. Everything listed is present at under 1%, and three of the four entries are below 0.05%. They are preservatives — isothiazolinones, the biocides that stop a water-based paste spoiling in the tub — and that chemical class is the one that carries skin-sensitisation classifications across water-based fillers, paints and adhesives generally. The SDS does not name a cause for the classification, so this page does not either, but it is worth understanding that a hazard classification can come from a fraction of a percent of a formulation.

Sensitisation is not irritation. Irritation is a local effect that stops when the contact stops. Sensitisation is the immune system learning to react to something: once acquired it is generally permanent, it is triggered afterwards by much smaller exposures, and it is built up through repeated everyday contact rather than through a single bad incident. On an exterior timber job — a run of weatherboards, a window frame, a deck edge — that repeated contact is exactly what happens when you press filler in and smooth it with a bare thumb, session after session.

The fix is unremarkable: wear gloves, and do not let the tub become the thing you dip your fingers in for an afternoon. The precautionary statements on the label also ask you to avoid breathing dust, which matters at the sanding stage rather than the filling stage, and to keep contaminated work clothing out of the house.

Protection

• Gloves — nitrile rubber, recommended by the SDS for intermittent contact, with the user making the final assessment.
• Eye protection — protective clothing including eye/face protection (P280).
• Ventilation — natural ventilation is adequate under normal use conditions; add a dust mask when sanding the dried filler.
• Keep out of reach of children. Avoid breathing dust, fume, mist, vapours or spray. Contaminated work clothing should not leave the work area, and should be washed before reuse.

First aid

Exposure	What to do
Eyes	Wash out immediately with water, holding the eyelids open, and keep rinsing. In all cases of eye contamination it is a sensible precaution to seek medical advice.
Skin	Effects may be delayed. Remove contaminated clothing and flush the skin and hair with running water. If swelling, redness, blistering or irritation occurs — including hours later — seek medical assistance, as that may indicate sensitisation rather than simple irritation.
Inhalation	Move the person to fresh air, keep them warm and at rest until recovered. Seek medical advice if effects persist.
Swallowed	Rinse the mouth with water. Do not induce vomiting. Give a glass of water to drink and seek medical advice. Never give anything by mouth to an unconscious person.

If poisoning occurs, contact a doctor or the Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand — with the container to hand. Selleys emergency line: 1800 220 770 in Australia, 0800 220 770 in New Zealand.

Common questions about Selleys No More Cracks Exterior Wood Filler

How long does it take to dry?

At 25°C, 2–3 hours for a 2–3 mm application. A 10 mm application takes 16 hours or more.

How do I fill a deep hole?

In 10 mm layers, allowing each to dry before the next.

Do I need to prime the timber first?

No. Priming is unnecessary before filling.

Can I stain it?

Yes, it is stainable and paintable. Remember that when tinting or staining, the final colour is not achieved until the varnish is applied — so judge your colour match after varnishing.

What colour is it?

A pine coloured paste.

What size does it come in?

A 450 g tub.

Can I nail or plane it?

Yes, it can be nailed or planed, and it is easy to sand.

What do I do about rotten timber?

Remove the rotten wood and fix any splits before filling. Filling over rot does not stop it.

Can I use it somewhere permanently wet?

No. It is not for permanently wet areas.

Can I use it in a joint that moves?

No. It flexes with the timber's own movement, but it is not for joints subject to movement.

What is the minimum temperature?

Do not use it below 5°C.

What if it rains before I paint?

Protect the repair from rain until it has been painted.

How do I clean up?

With water, before the filler dries.