I'm planning on using a 600 x 600 mm tiles as a worktop surface applied to a piece of 15mm mdf. My question is should I use a tile adhesive or a mastic glue to fix them down.
From your posts you seem to be new to DIY. I'd suggest that you google johnbridge.com, an American tile forum where work top/counter top tile is expertly dealt with. Maybe put your proposal to them.
If your w/t has cut-outs, fixtures and returns, then it could get a bit complicated, but well doable for a DIY'er.
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