Just started on this in the traditional picture frame with Polyfilla Large Cracks for the concrete. The concrete has been painted a darker shade than the MInenraumer so will be using Tamiya AS18 spray can as I have some of that laying around but may paint a satin varnish over it possibly.
Done a basic plan of how the concrete is done in slabs to help when I do the polyfilla. First off is some varnish to seal the cheap mdf that you get as a base in these frames.

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