I think cork is too "spongy" but it's worth a try if you go into it knowing it might not last.

Maybe hope it's attached to a thin wafer-board or something, and take the cork OUT completely? Probably better. Thanks.

One of the early projects when I was experimenting w/mosaics, I mosaiced a $5.00 garage sale lamp that had a cork base. It was quite solid. Here's the picture. This was done w/the ready-mix grout/adhesive, hence white grout. This reminds me to paint that grout when I get time.