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

Selleys No More Cracks Exterior Powder Filler is a cement based powder filler that you mix with water before use, made for exterior cracks and holes in bricks, cement, stone and other masonry surfaces. Once set it is waterproof, resistant to temperature and humidity changes, and can be sanded, nailed or screwed.

Two things follow from it being a powder rather than a ready-mixed paste, and they are the two things worth knowing before you start. First, you control the consistency — which matters more than it sounds for deep repairs. Second, once mixed you are on a clock: the paste stays workable for approximately 30 minutes, so you mix what you can use rather than the whole bag.

What the key numbers mean in practice

• Mix ratio: roughly 4 parts powder to 1 part water. For deeper cracks, use less water to give a firmer mix.
• Workable for approximately 30 minutes once mixed.
• Drying time: 5–6 hours, depending on humidity.
• Grey when set, which matches cement.

The instruction to use less water for deeper cracks is the most useful detail on the page. A wetter mix is easier to spread but slumps — in a deep vertical crack it sags away from the top of the repair before it sets. A firmer mix stays where you press it. Match the consistency to the job: looser for shallow surface work, stiffer for deep holes.

The 30 minute working time and the 5–6 hour drying time are doing different jobs. Thirty minutes is how long the mixed paste stays usable in your bucket. Five to six hours is how long the repair takes to dry in the wall before you can sand it. Humidity extends the second figure — on a damp day, expect to come back later than you planned.

Being waterproof once set is what separates this from an ordinary wall filler. It is why the same product is listed as suitable for wet area applications as well as exterior masonry, and it is also why it resists the temperature and humidity swings that an exposed wall goes through.

Where to use it

Selleys lists it for filling cracks and holes in:

• Bricks
• Cement
• Stone
• Other masonry surfaces

It is suitable for both interior and exterior masonry repairs, and once set it is suitable for wet area applications. The grey colour is deliberate: it matches cement when set, so on unpainted masonry, mortar or render the repair is less conspicuous than a white filler would be.

The fact that it can be nailed or screwed after cure is worth noting, because most wall fillers cannot. If you are making good a hole in masonry that later needs a fixing near it, a cement based filler gives you something to fix into rather than something that crumbles.

For a ready-mixed alternative on exterior masonry, see No More Cracks Exterior Brick & Render on the wall filler page. Selleys also has a general guide to filling cracks in masonry walls.

How to apply it

1. Make sure the surface is clean, dry and free of loose or powdery material. Cement based filler needs sound material to key into.
2. Mix the powder into a paste — typically around 4 parts powder to 1 part water. For deeper cracks, use less water for a firmer mix.
3. Use it within about 30 minutes. Mix in batches you can apply inside that window.
4. Press the filler into the crack or hole with a filling blade or scraper and remove the excess. Removing excess as you go is the cheapest sanding you will ever do.
5. Allow 5–6 hours to dry, depending on humidity.
6. Sand the surface with medium-grade sandpaper once dry.
7. Remove all dust after sanding before painting — dust left on the surface stops paint adhering properly. For best results apply an undercoat before your top coat.

Limitations

• Where movement occurs, use a flexible filler such as Selleys No More Gaps. A set cement based filler is rigid. If the crack you are filling is still moving — a control joint, a junction between two different materials, or a crack that has widened over time — a rigid repair will crack again along the same line.

This is the judgement call to make before you mix anything. Ask whether the crack is a finished defect or an ongoing movement. A rigid filler is right for the first and wrong for the second, and no amount of care in the application changes that.

Clean up

Clean up is with water. Do it before the filler sets — a cement based product that has gone off in a bucket or on a blade has to be removed mechanically.

Hazard classification

Classified as hazardous under Safe Work Australia GHS 7, with the signal word Danger — the higher of the two GHS signal words, and the only product in this filler range that carries it.

• Eye damage/irritation — Category 1. H318: causes serious eye damage.
• Skin corrosion/irritation — Category 2. H315: causes skin irritation.
• Specific target organ toxicity, single exposure — Category 3, respiratory tract irritation. H335: may cause respiratory irritation.

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)
Cement, Portland, chemicals	65997-15-1	10–30%
Ingredients determined to be non-hazardous or below reporting limits	—	Balance

H318 is the classification to take seriously. It is not “serious eye irritation”, which is the Category 2A wording used on several of the ready-mixed fillers in this range; it is serious eye damage, meaning effects that may not be reversible. Portland cement is the only hazardous ingredient the sheet lists, and cement is the reason the classification sits a full category higher than its stablemates: mixed with water it goes strongly alkaline, and alkali injuries to the eye keep penetrating after the contact rather than stopping at the surface. That is also why the first-aid advice below is fifteen minutes of irrigation and a trip to hospital rather than “rinse and see how it feels”.

The comparison worth drawing is with No More Cracks Interior Powder Filler, which looks like the same kind of product — a powder you mix with water — but is not classified as hazardous at all. The difference is the cement. Do not carry habits from the interior product across to this one.

The exposure happens at the step the directions above describe as mixing roughly four parts powder to one part water. Tipping and stirring dry cement-based powder raises dust, which is where H335 comes from, and dust in the eye is the realistic way a serious injury happens on a domestic job — not a splash. Wear sealed goggles rather than open safety glasses while you mix, mix outdoors or in a well-ventilated spot, wear a dust mask, and keep your hands away from your face until you have washed them. Sanding the set repair, which the page also calls for, raises dust of its own; keep the mask on for that.

Wet mixed paste on the skin should be washed off rather than left to dry, for the same alkalinity reason. Kneeling in it or letting it sit inside a glove or a boot is how cement causes burns on building sites.

Protection

• Eye protection — goggles or eye/face protection, worn from the moment the bag is opened. This is the one item not to skip on this product.
• Dust mask or suitable respirator — while mixing the dry powder and while sanding the set filler.
• Gloves — nitrile rubber; suggested by the SDS as suitable for intermittent contact, with the user making the final assessment.
• Ventilation — mix and work in a well-ventilated place so dust does not accumulate.
• Overalls and safety shoes on larger jobs. Wash hands before eating, drinking or smoking, and wash contaminated clothing before reuse.

First aid

Exposure	What to do
Eyes	Immediately irrigate with copious quantities of water for 15 minutes, holding the eyelids open. Remove contaminated clothing and wash the skin. Urgently seek medical assistance and go to a hospital or medical centre — do not wait to see whether it settles.
Skin	Remove contaminated clothing immediately and flush the skin and hair with running water. Keep flushing for at least 15 minutes, or until advised to stop by a doctor or the Poisons Information Centre, then go to a doctor or hospital if needed.
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 Powder Filler

How much water do I add?

Typically around 4 parts powder to 1 part water. Use less water for a firmer mix when filling deeper cracks.

How long can I use the mix for?

Approximately 30 minutes once mixed. Mix only what you can apply in that time.

How long does it take to dry?

5–6 hours, depending on humidity.

Is it waterproof?

Once set, yes. It is a waterproof formulation and is suitable for wet area applications once set.

Can I use it inside?

Yes. It is suitable for both interior and exterior masonry repairs.

What colour is it?

Grey — it matches cement when set.

Can I nail or screw into it?

Yes, after cure. It can be sanded, nailed or screwed.

What surfaces is it for?

Bricks, cement, stone and other masonry surfaces.

How do I sand it?

With medium-grade sandpaper, once dry.

Do I need to do anything before painting?

Remove all the sanding dust first, so the paint adheres properly. Applying an undercoat before the top coat gives the best result.

Can I use it where the crack is still moving?

No. Where movement occurs, use a flexible filler such as Selleys No More Gaps.

How do I clean up?

With water, before the filler sets.