What is Selleys Fireproof Cement, and where should you use it?

Selleys Fireproof Cement is a fire-resistant cement for the interior filling of stoves, fireplaces and chimneys. It is a thick white paste that resists intense heat and cleans up with water.

The single most important thing to understand before you buy it is what it is not. Fireproof Cement is not an adhesive — it is a filling compound. It fills holes and cracks inside a firebox; it does not bond components together, and it should not be relied on to hold anything in place. If your job is sticking something back on, this is the wrong product no matter how well it handles heat.

Where to use it

• Interior filling of stoves
• Interior filling of fireplaces
• Interior filling of chimneys

Note the word "interior" in every one of those. It refers to the inside of the appliance or flue — the surfaces that see the fire — and it also marks the boundary of the product's approved use. The manufacturer's limitations rule out external appliances explicitly.

How to apply it

1. Remove dust, grease and loose debris from the area to be filled. Soot and loose material are exactly what a filler cannot key into.
2. Dampen the cavities for better adhesion. This is a water-based product going into dry, absorbent, often porous masonry; a dry cavity draws water out of the paste before it can bond.
3. Apply firmly into the holes and cracks with a damp knife or spatula. Firmly is the operative word — the material needs to be pressed into the void rather than laid across it.
4. If the paste is stiff, loosen it with a little water.
5. Trim off any excess before cure, and clean away residues with a damp rag while the product is still uncured.
6. Allow to dry for at least 48 hours before exposure to heat.

Why the 48 hours matters

Of all the instructions above, the 48-hour dry time before heat is the one that decides whether the repair holds. The product is applied wet, and water has to leave it before the fire goes in. Lighting a stove on a fill that is still carrying moisture drives that water off as steam from inside the material, which is a good way to crack or blow out a repair that would otherwise have lasted. Forty-eight hours is a minimum, and a deep or thick fill in a cold, damp room is a case for allowing longer rather than less.

The instruction to trim the excess before cure follows the same logic in reverse. Once the material has hardened it cannot be resoftened with water, so a bead of surplus cement smeared across the face of a firebrick becomes a mechanical removal job. A damp rag two minutes after application saves that entirely.

Limitations — where Fireproof Cement should not be used

These are the manufacturer's stated limits. Three of the four rule out applications people commonly assume a "fireproof" product will cover.

• It is not an adhesive. It is a filling compound and should not be used to bond or hold components.
• Not recommended for external use — for example, barbecues and incinerators.
• Not suitable for use in kilns.
• Not recommended for moving joints, such as expansion joints, as it sets rigidly.

That last point is worth dwelling on, because it is the failure most likely to look like a product fault. A rigid filler in a joint that expands and contracts with each firing cycle will crack, and refilling it will produce the same result. Where a joint is designed to move, it needs a product that moves with it, not a rigid one applied more carefully.

The kiln and barbecue exclusions matter for the same underlying reason: they are different service conditions from the interior of a domestic stove or fireplace, whether through sustained temperature, weather exposure, or both. "Resists intense heat" is a description of the product's behaviour in its intended application, not a licence to use it anywhere hot.

Clean up

Clean uncured product with water, and clean away any residues with a damp rag before the product cures. Trim off excess before cure.

Once it has hardened, the material cannot be resoftened with water. That property is exactly what you want in a firebox and exactly what makes late clean-up difficult, so it is worth having a damp rag on hand before you start rather than fetching one afterwards.

Hazard classification

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

• Eye damage — Category 1. Causes serious eye damage.
• Skin irritation — Category 2. H315: causes skin irritation.
• Specific target organ toxicity, single exposure — Category 3, respiratory tract irritation.

What is in it

Chemical entity	CAS number	Proportion (w/w)
Silicic acid, sodium salt (sodium silicate)	1344-09-8	10–30%
Non-hazardous or below reporting limits	—	Balance

This is a sodium silicate cement — water glass. Sodium silicate solutions are strongly alkaline, which is why a product that looks like grey paste carries an eye damage Category 1 classification.

Alkali injuries to the eye are more serious than acid ones because they keep penetrating tissue rather than self-limiting. A splash needs an immediate and prolonged flush, and medical attention.

The respiratory tract irritation classification matters for the way this product is actually used: sealing stoves and fireplaces means working in a confined firebox, often kneeling with your head inside it. Ventilate and avoid breathing the vapour, and keep your face out of the opening while applying.

Once set and fired, the cement is inert. The hazards belong to the wet material.

Protection

• Gloves — nitrile rubber; essential wherever a sensitisation classification applies.
• Eye protection — chemical goggles or safety glasses.
• Ventilation — work in a well-ventilated area; do not work in a confined space.
• Wash hands before eating, drinking or smoking, and wash contaminated clothing before reuse.

First aid

Exposure	What to do
Eyes	Rinse immediately and continuously with water for at least 15 minutes, holding the eyelids apart. Remove contact lenses if present and easy to do, then keep rinsing. Immediately call a Poisons Information Centre or doctor. This product causes serious eye damage and the injury is not always obvious at first.
Skin	Wash with plenty of water. Remove contaminated clothing and wash before reuse. If irritation develops, get medical advice.
Inhalation	Move to fresh air. If irritation persists, seek medical advice.
Swallowed	Do not induce vomiting. Rinse the mouth and seek medical advice immediately.

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 Fireproof Cement

Can I use it to glue a firebrick back in place?

No. Fireproof Cement is not an adhesive — it is a filling compound.

How long before I can light the fire?

Allow the repair to dry for at least 48 hours before exposing it to heat.

Can I use it on my barbecue?

No. It is not recommended for external use, and barbecues are given as a specific example, along with incinerators.

Can I use it in a kiln?

No. It is not suitable for use in kilns.

Will it survive a joint that moves?

No. It sets rigidly and is not recommended for moving joints such as expansion joints.

What does it look like?

A thick white paste.

How do I get it into a deep crack?

Apply it firmly into the holes and cracks with a damp knife or spatula, after dampening the cavity. Dampening improves adhesion.

The paste is too stiff to work. What do I do?

Loosen it with a little water.

How do I clean up?

With water, while the product is still uncured. Trim off any excess before cure and wipe residues away with a damp rag.

Can I soften it again after it has set?

No. Hardened material cannot be resoftened with water.

Does the surface need cleaning first?

Yes. Remove dust, grease and loose debris before applying.

Is it suitable for the outside of a fireplace?

The product is specified for interior filling of stoves, fireplaces and chimneys. For gaps and cracks in exterior brickwork and mortar, a different product is required.

For repairing cracks in brickwork and mortar outside the firebox, see No More Gaps Bricks & Mortar. The rest of the specialist range is under specialist fillers and putty.