Tanking - waterproofing the walls prior to tiling a shower
Tanking is the term used to waterproof the walls within a shower cubicle or a shower area prior to tiling... or indeed any other area of wall or floor that requires waterproofing.
Tanking involves applying a waterproof membrane over the surface to be tiled. This membrane is usually applied in the form of a special rubberised liquid that is brushed on. Once cured, not only does this membrane bond extremely well with the underlying surface and form a protective waterproof layer, but it also in turn provides a sound surface on which to tile.
Plasterboard and plaster will gradually disintegrate if they are continually exposed to water, which means that over time any water that finds its way behind the tiles, past the waterproof adhesive and on to untreated plaster or plasterboard surface will eventually cause the tiles to come adrift and possibly even even fall off altogether.
Not many people realise this, but most grouts are to some extent mildly porous. This is not a fault as such, but rather the nature of grout. This is normal and is not an issue if the walls have been prepared correctly and tanked as any moisture finding its way past the grout has nowhere to go that it can do any damage. Over time grout can sometimes develop hairline cracks at tile/grout boundaries, which is where the real problems can arise if the underlying wall has not been tanked. However, if the wall has been tanked and the correct tile adhesive used, then even these hairline cracks in the grout are unlikely to pose a problem as any water ingress is halted at the tanking membrane. This water will be absorbed by the porous backs of the tiles which will simply dry out when the shower is not in use.
As in many things the key to longevity is preparation, and tanking walls within shower areas is extremely important in this respect. Obviously tanking a shower area comes at some cost in terms of both materials and the extra work involved, but in the long run it is money very well spent.
Many bathroom fitters, shower installers and tillers quite often cut corners here and neglect to apply a tanking membrane, either because they don't know any better or because this way they can put in a lower quotation and so undercut their competitors - and of course the client will be quite oblivious to this fact. The truth is that once the tiles are in place you cannot possibly tell whether or not the wall was tanked prior to tiling... only time will tell.
All this is just to say that tanking a shower area prior to tiling is not something that should disregarded, neither should it be an option - on the contrary, it is something that should be done as a matter of course.
- - Suffice to say, I always tank any walls within a shower cubicle or a shower area as a matter of course - -