1: Make or buy a casting frame (box).. To make one, screw four pieces of batten to a backing board.. Ensure a tight fit to avoid leakage.. Do not use glue as it is essential to be able to dismantle the frame later..

2: Cut a piece of heavy brown paper slightly smaller than the internal dimension of your frame, allowing a grout space around the edge..

3: Draw your design on the paper & trace through to the other side, leaving a mirror image to assemble the mosaic on..

4: Using a 50:50 PVA water mix glue the tesserae face down onto your design.. In some cases where the biscuit of different tiles is the same you may need to mark them some way, (I use a thin acrylic paint wash on the backs of the tiles before cutting so I know what colour I'm using).. When the mosaic is assembled, let it dry thoroughly..

5: Spread petroleum jelly evenly & thoroughly over the inside of the frame.. This acts as a release agent, ensuring the finished work doesn't stick to the wood..

6: Place your mosaic onto the base of the frame, paper side down.. Centre it with an even gap around the edge, (the petroleum jelly stops things from sliding around)..

7: Pregrout. Mix a slurry, (grout or cement) a bit runnier than the normal mix.. Push it into all the joints and sponge off enough to expose the biscuit backing the tesserae..

8: Mix together 1 part cement (by volume) with 2.5 parts sand.. Add water until the mixture is firm but workable, with no water running out of it.. Apply to the back of the mosaic and fill to half way up the frame..

9: Place some sort of metal mesh or chicken wire on the cement mix, to give your slab strength.. The mesh should be galvanized or rust proof on some way as rust stains the work.. Fill the frame to the top with more cement and smooth off the surface..

10: Wrap the slab in plastic and seal it for at least a week to set..

11: Unwrap the slab, carefully unscrewing the frame & inverting the work..