Cracks in the Gasbeton*, the white layer under the fire brick is common and not a performance issue. It’s lighter more brittle than fire bricks but it’s an excellent heat conductor and insulator that helps keep the fire bricks hot. Sometimes the Gasbeton needs to be broken to fit through the oven door. A simple crack is the same as the seam between two pieces.
*****GASBETON® is an aerated autoclaved concrete with excellent thermal insulation and low environmental impact.
