Refractory mortar and wood fired ovens.

For high quality oven, refractory mortar should be used in only up to ¼" (6mm) thick application. Mortar only assist in forming firing chamber and shouldn't be used or exposed on the inside hot-face. Refractory mortar should not be used to plug holes or big spaces between firebricks. Body of firebricks face the heat. Thicker mortar applied always shrinks*, shrinkage would create increased brick movement/gap between cold state and state expanded by heat. Every time this gap happens bricks change position, just a little bit but enough to cause rebuilding job in the future.

Before work with firebricks and mortar
dip bricks in water.

* Firing linear mortar shrinkage of up to 8%

Refractory mortar recipes.

10 : 3 : 1.5 - Sand, Calcium Aluminate cement, Fireclay.

If you found hard to locate refractory cement don't worry here is recipe with Portland cement available in ordinary building stores. There are two Portland cement types, get the common gray in color, the other one is white used for around pools etc. where a white effect is required. Lime is calcium it takes over the cement in hot conditions (Portland will gradually burn out, it is used only for the mortar to set while working.)

10 : 6 : 2 : 3 – Sand, Fire Clay, Portland cement, and Lime.

Mixing heat resistant mortar.

(Fire clay explained.) Mix first all dry ingredients well, in small amounts start add clean room temperature water, and mix into peanut butter consistency. Thin application between firebricks and only where needed e.g. in "V" sections between arched bricks on outside. Inside the arch - these bricks should be in line next to each other touching without gaps. No need for mortar between floor and wall bricks, in barrel shape dome you will not use too much mortar in arch too - it's very easy. But if you do a round dome make sure you don’t get spaces in between bricks exposing mortar on inside the dome and big thickness of mortar on outside - start to angle cut bricks as soon as gaps begin to occur. In any case on inside of dome there shouldn't be any gaps. Only a small amount of mortar should always be used for it to stay strong. (When buying firebricks ask your refractory supplier about it too.)

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