Builders and tilers are often surprised to learn that tiled surfaces cannot be guaranteed waterproof.
Impervious grout and water-resistant adhesive don't necessarily stop water seeping through into the fabric of a building, especially where modern, high-performance power showers throw out a lot of water at high force, so you do need to ensure that the walls have been properly waterproofed.The British Standards Institution (BSI) recommends the use of impervious membranes such as the polyethylene Schlüter-KERDI and Schlüter-DITRA. BSI also says that further advice should be sought from specialists in the waterproofing field. As the world market-leader in tiling accessories, Schlüter-Systems Ltd. is regularly called upon by specifiers to advise about waterproofing on particular projects.
Generally, waterproofing is a matter of education -- first of all about the overall need for it, and secondly which type of membranes to use. For instance, as well as protecting tiled walls, Schlüter-KERDI also protects surfaces such as renders, plasters and plaster-board, whereas Schlüter-DITRA can be used for uncoupling tiled floors from problematic substrates, such as timber.
All householders who've suffered water damage because of the lack of waterproofing would readily agree that prevention is better than the cure. The problem is that many builders don't offer waterproofing as an option in the domestic market, yet our research shows that the public generally think of a tiled surface as being waterproof.
There are other forms of waterproofing, which include brush-applied liquids. This, essentially, does the same job as the flexible membranes quoted in the BSI code, but will normally take longer, because each coat usually requires a drying time before tiling can start.
If you use Schlüter-KERDI, it has a fleece fabric on both sides, for easy anchorage into the tile adhesive. It doesn't rot, doesn't become brittle, and because it is extremely flexible it can bridge over cracks. Press the membrane into the adhesive over the whole surface, the fleece on the underside of the membrane needs to be solidly embedded into the adhesive so that its entire surface is bonded. Work the membrane into the adhesive, in just one direction, using a float or screed trowel. The perimeters and any membrane joints are then sealed using the waterproof sealing band Schlüter-KERDI-KEBA, which must be adhered with Schlüter-KERDI-COLL, to provide a guaranteed waterproof installation, and once the area has been fully sealed, tiles can be laid on top immediately afterwards. Special sections of Schlüter-KERDI are available for internal and external corners.
You'll make additional profit on the job, and if everything is installed correctly your customer will have a properly waterproofed installation.