Would you recommend the installation of a water proof membrane on shower walls?

Hello Paula

Should the wall surface you are tiling your slate onto be constructed of either plaster or plasterboard then to protect from water damage yes, a waterproof membrane would be required.

As a product suggestion for you, Mapei UK produce a product called Mapelastic Aquadefense, this product is very easy to apply, simply like when applying emulsion a wall.

Should you require further help or information on this product please call our office on 01283 730388 and ask for Becky.