Airset Refractory Mortar
Airsetting Refractory Mortar 25kg: designed for use in kilns and furnaces
The internal structure of the kiln is laid in fire brick, with extremely tight mortar joints (1-2mm). The sodium silicate in the mortar then reacts with the surrounding air and causes the mortar to take an initial set, allowing the kiln or furnace to be fully constructed. The structure is then fired to its full operating temperature (around 1500°C) and the airset mortar vitrifies, fusing to the surrounding bricks and becoming a ceramic.
If you’re building a Wood Fired Oven or Fireplace, you’ll need to make a hybrid mixture of airset refractory mortar, GP cement, lime and fine washed sand.
There are several reasons why:
1. You simply cannot get a Wood Fired Oven hot enough to vitrify the mortar. Without this firing the mortar will never set fully hard and will revert to a soft, clay consistency if it gets wet.
2. Unless you spend weeks precision cutting every brick to size, you’re going to have wedges of mortar in your oven (sections that taper from a tight joint on the inside face, to a large joint on the outside, sometimes up to 25mm). If you tried filling a wedge like this with pure refractory mortar you would see drying shrinkage cracking on the outside of the joint, and the mortar bond would be weak.
The Hybrid Mixture detailed below has been tried and tested for years, and works extremely well. Even so, we insist that our customers only use this mortar if the inside face of the joint is tight – if the mortar started to deteriorate in 20 years, with a tight joint on the inside face, the mortar will be locked in a wedge and the integrity of the joint will remain.
Hybrid Mortar Mixture for Wood Fired Ovens & Fireplaces
2 Parts AirSet Refractory Mortar
2 Parts Fine Washed Sand
1 Part General Purpose (GP) Cement
1 Part Hydrated Lime
(Parts by volume)