How to make fireproof mortar from wood ash

A mortar made from cement and sand or clay alone is not suitable for plastering a brick oven with a metal hob. It will quickly crack, which will impair the operation of the stove and even pose a danger to people. You need a mix based on wood ash.

Making fireproof mortar

We start by sifting the ash to remove small pebbles, nails and other materials whose presence is undesirable in the final product. It would also be a good idea to pass the liquid slaked lime through a sieve, since it may also contain foreign particles.

We prepared 6 liters of ash and 5 liters of slaked lime. Add 1 kg of table salt to the container with the ash, mix thoroughly and pour slaked lime into the resulting mixture, and mix thoroughly again.

The resulting mix contains 6 liters of sifted wood ash, 3-4 liters of lime milk and 1 kg of table salt. The consistency of the finished solution should resemble flour dough of medium consistency, that is, not very thick, but not liquid either.

Using a chisel and hammer, we break it up, and with a flat brush we sweep away the poor-quality coating, which is prone to cracking, around the hob with burner rings. Then we moisten the perimeter of the hob sufficiently with water to the width of the solution, distributing the moisture evenly over the entire surface, including the stove itself.

Using a narrow and wide spatula, evenly distribute the prepared solution based on wood ash, lime milk and table salt around the perimeter of the hob. We level the mixture, focusing on the thickness of the hob.

Let the applied plaster sit for a while and heat the oven. This will cause the steel or cast iron cooktop to heat up and expand. If this is not done, the stove may break the applied solution during operation of the oven.

The resulting solution can also be used to cover cracks on the hob. After the furnace has cooled, microscopic gaps can be observed between the plate and the solution as a result of thermal expansion of the metal and its subsequent cooling. These cracks do not pose any danger, because after heating the oven, they disappear.