Tiling on self levelling screed

The decoupling membrane people would recommend you use their products, however this is not strictly necessary! It works like this: if a cement based adhesive is applied to an anhydrite screed the adhesive reacts with the gypsum in the screed, a mineral layer is formed at the surface and the tiling adhesive will not bond. This is simply overcome. Yes you can insert a decoupling membrane, but you can also just treat the surface then tile straight onto the screed. Its vital that you measure the moisture content of the screed, for decoupling membranes it must not have a residual moisture of more than 2%, for tiling directly to the screed it must not exceed 0.5%! (this is why the membrane guys ‘sell’ their ‘solution’). So wait until your screed is measured by a moisture meter at being less than 0.5% moisture then you have to really make sure you brush off the layer of laitance (this is a mechanical process – there are no easy chemicals!) then you must treat the surface with the correctly specified primer repeatedly until no more primer can be absorbed. Once dry you can tile directly to this without a membrane. (if you have underfloor heating under that screed you need to use a fully flex adhesive to fix your tiles)