Oven floor repair help

I am repairing an old brick oven, the cooking floor was previously just a large steel plate sitting on top of a concrete base…
After some research on this site and others, I plan to lay calcium silicate board on top of the concrete, then the sand layer, then fire brick layer.
However the concrete is quite badly damaged, eroded, and very uneven. I’m wondering if anyone has any helpful tips or ideas on how I might manage this, anything I could use to level the concrete to place the calcium silicate board on top.
Any other suggestions welcome, thanks

Welcome to the BrickWood forum!

It sounds like you are rebuilding on at least part of the BWO plans, which will get you a much more useful hearth than was previously there.

Based on what you describe, I’d suggest the following:

  • Repair any through cracks or holes in the concrete with type S mortar. Don’t worry about leveling or smoothing, just get an intact surface.
  • Use self-leveling concrete—enough to reach the high point of the uneven surface and thus make a new surface. Let it cure according to manufacturer’s instructions.
  • Lay your calcium silicate board on top of the now-level concrete surface, then sand, then firebrick in a herringbone pattern.

In this method, you are ensuring that the concrete will not erode any further and you will obtain the level surface you need to proceed.

Hope this helps. If you can, please share a photo or two of your project so we can see it.