cob oven floor

I found donor floor tiles for my to build wood fired oven. It was used for over a century in an old French farm. The top of the tile is kind of damaged. Can they be saved for use, for example by applying a thin layer of cob?

It's good to reuse old materials. However, in this case, I don't think they will be usable as floor tiles. You can make a nice smooth surface with cob applied over the tiles, but it will never be strong and abrasion-resistant. You may be able to use them as part of the walls/dome of the oven where smoothness is not important.

Hi Mika,

Welcome to Permies.

How even are the backs of the tiles? Could that side be used?

I recall a story about someone wanting to get more use out of a stone slab at the door of their old house which was worn hollow, flipping it over, and finding that the other side had already been worn hollow. Someone long ago had the same reuse idea

The back of the tiles cause problems too, which would need the same treatment.   Would it be an option to redo the cob application every other year? The diameter of the inside of the oven will be 24 inch, so not a lot of surface to redo.

If you can be gentle with the cob surface and won't mind clay dust or sand occasionally on your baked goods, you can try it. A thick layer of cob will be more durable than a coat that just covers the holes in the tiles. I would make it at least 1 cm, maybe 2. There is no telling in advance how long the cob surface will last.

If you are making a traditional cob oven that has a fire inside the oven chamber, some of the cob may get baked into soft pottery similar to the tiles. You may be able to run a large very hot fire for several hours and bake much of the cob to pottery. The doorway will be the hardest part to fire, since cold air will be coming in there. I would put some good solid tiles in the front floor and doorway to be the finished surface there.

Thanks Glenn, for your insights. Maybe a few too many uncertainties with the cob layer solution, right? Hopefully I can find some tiles in a better condition.