At the start of the heating season it is worth checking the stove, fireplace and flue: a crack in the masonry or at a pipe joint lets smoke and carbon monoxide into the room. Ordinary silicone or acrylic burns out in a firebox at the first firing, so a stove needs a fire-resistant sealant, also searched for as a refractory sealant. LACRYSIL makes the Fireplaces and Stoves silicate sealant, with a working range of -50…+1500 °C.

Silicate sealant versus silicone

Its base is silicate, chemically closer to water glass than to polymers. The most heat-resistant LACRYSIL silicone sealant is rated to +130 °C, so silicone is never used where it meets open flame. The Fireplaces and Stoves joint lets through neither smoke nor gases. It contains no asbestos: dust from a failed seal in the hot-air zone would go straight into the room.

Where it is used

Cracks, gaps, joints and seams in stoves, fireplaces, fireboxes and flues. It is also used to repair car and motorcycle exhaust systems. It bonds well to brick, concrete, metal and fireclay.

How to seal a crack in a stove

The sealant is applied at +5…+35 °C, so let the stove cool first. Joint depth is up to 5 mm. It dries in 24–48 hours, after which the stove is fired: only exposure to flame or high temperature makes the joint water-resistant and elastic. The joint is black. One 0.55 kg cartridge covers 17.6 m of a 4×4 mm joint. Shelf life is 18 months, so a cartridge bought before the season can be kept in reserve.

Questions and answers

Do I need to fire the stove after sealing?

Yes. A dry joint becomes water-resistant and elastic only after exposure to flame or high temperature.

Will it fill a wide crack?

The maximum joint depth is 5 mm. Deeper cavities are not filled with this sealant.

Can a stove crack be sealed with silicone?

No. Silicone is rated to +130 °C and does not work in the fire zone.

How many cartridges do I need?

Working it out from joint length and size is explained in “Sealant consumption per metre of joint”. Other LACRYSIL sealants are in the sealant catalogue.