Tile fixers often feel that using a water-resistant adhesive or grout will be good enough to provide a waterproof finish in bathrooms, shower rooms and wet areas, but that's not the case.
During the numerous training courses we deliver to the flooring industry - many under the RIBA Continuing Professional Development Programme - we regularly include the fact that a tiled surface cannot be guaranteed as waterproof. As soon as that point is raised, we are often asked the following question:
"So how can I ensure that my work is waterproof?"
While there are types of brush-applied liquid waterproofing systems which offer a degree of waterproofing, the British Standards Institution suggests using impervious membranes. BS 5385 states: "Tiles and bedded finishes, even when the joints are filled with impervious grout, cannot be guaranteed to eliminate entirely the passage of liquids downwards...in the case of suspended floors water passing downwards may cause dampness on walls and ceilings below, and in the worst cases leads to flooding."
It says the most satisfactory method of preventing this is by: "Providing a membrane between the base and the tiling...the membrane should be impervious...and be sufficiently flexible and strong enough to resist movement in the structure, and loads, without rupturing." It concludes by saying that further advice should be sought from specialists in the waterproofing field.
TIPS ON INSTALLING WATERPROOFING
A correctly installed waterproofing membrane would prevent water ingress damage. There's also a need for waterproofing where floors have to be washed regularly - even more so where chemicals are used, in places such as breweries, dairies and food processing plants.
And, indeed, waterproofing should be considered even for domestic bathrooms nowadays, especially with the growing use of power showers which throw out a lot of water at high pressure. Schlüter-KERDI is ideal for waterproofing walls, and is as simple to install as wallpaper, whilst Schlüter-DITRA is recommended for floors, due to its uncoupling capabilities.
If you're using Schlüter-DITRA - the type of impervious membrane as recommended by BSI - the installation technique is simple. After ensuring that the substrate is even and load-bearing, the bonding adhesive is applied with a 3mm x 3mm, or 4mm x 4mm notched trowel. While the type of bonding adhesive depends on the type of substrate, for most substrates a dry-set tile adhesive is suitable.
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.