Fire bricks lifting

[Alliance66]

Hi all, just want some advise, I have noticed recently that a few of the fire bricks on its base of my pizza oven are lifting when in use, which is rather annoying, as the moment I just tap them down with a mallet but wanted a more permanent solution, I have tried cementing but no good, any suggestions is appreciated.

[JRPizza]

Any pictures and descriptions of how your oven was constructed would be helpful. Normally the bricks are held down by their weight and don't move. As Newton said, objects at rest tend to stay at rest.

[Timothy_W]

Hello. How much do bricks rise? What material is under the bricks? It is possible that the problem is not with the bricks themselves, but with the material underneath. The material expands from heat and displaces the bricks.

[david s]

You don’t say what material you have under your bricks, but I do know from experience that vermicrete certainly can swell if fired too hard before it is dry. Because it is so water absorbent (by volume it takes 3 parts water for every 10 parts vermiculite). If significant amounts of water suddenly turn to steam the vermicrete swells and cracks. Other insulating materials could also do the same.
This is why I recommend drain holes in the supporting slab and a ventin the dome insulation layer.