Waterproof tile sealant?

Does anyone know if a waterproof (oil based) tile sealant is available. My bathroom tiles around the shower have been applied to wood and the water is leaking behind the tiles and into the cupboard behind.

Yes the previous owners were wrong to do this and no i cant afford to build a new wall (well not this year anyway). I need to be able to seal the tiles with some type of clear varnish/lacqeur which is waterproof and for application on top of tiles it obviously need to be clear......

I know of a waterbased sealer (clear) two coats are required. final stage is a clear two coats of polish. available from Homebase.
Lee.

p.s wear eye protection and gloves as i got some in my eyes and had problems for a week

How did you get on with your shower i have the same problem. did you find anything that worked?

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