Why do the insulation tiles (vermiculite) in the combustion chamber crack?

There may be several reasons why the vermiculite tiles crack. The typical causes are natural wear, overheating or vermiculite exposure to moisture. There may be several reasons why the vermiculite tiles crack. The typical causes are natural wear, overheating or vermiculite exposure to moisture.

Natural wear and tear

The yellow tiles in the combustion chamber are naturally prone to wear and should be replaced if cracks are more than 0.5 cm wide. If the cracks are not larger than 0.5 cm across, cracks and splits in the tiles will not have any effect on the stove's insulation capacity. Lifetime of the tiles depends on how often and how heavily the stove is used. You can replace the tiles yourself, as these are sold in complete ready-to-use sets. These sets can be purchased from our dealers or online here.

Overheating can affect the vermiculite

Vermiculite is a natural material which is why its appearance and physical properties can change if it is exposed to very intense heat for prolonged amounts of time. The color of vermiculite changes as it reaches higher temperatures. A dark, reddish vermiculite can indicate that the stove was overheated.

If vermiculite is overheated it will become:

• More fragile – it will break easily if exposed to changes of temperatures or pressure from the expanding metal inside the fire chamber.
• More brittle - it will break easily if hit accidentally while loading the stove.
• Less effective - it will lose its ability to isolate the stove, which leads to a loss of efficiency.

Moisture can affect the vermiculite

If the vermiculite is exposed to moisture, its lifespan is shortened. Vermiculite may be exposed to moisture if you use wet wood or through condensation in the chimney.

Chimney sweeping

During chimney sweeping, the soot lands in the stove. Often, the soot will land behind the rear insulation tile, meaning there is no room for the steel to work. This can result in the tile cracking.