ENSURING TILED INSTALLATIONS ARE WATERPROOF - Ditra and Kerdi Drain
By IAN KNIFTON, Technical Manager, Schlüter-Systems Ltd., world market leader in essential tiling protection
People are often surprised to learn that tiled surfaces cannot be guaranteed waterproof without special, additional protection.
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 it is essential to ensure that both the floors and walls in wet areas have been properly waterproofed.
The British Standards Institution (BSI) recommends the use of impervious membranes to guarantee a waterproof surface – however, BSI also says that further advice should be sought from specialists in the waterproofing field.
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 some are designed specifically for walls; others waterproof floors while performing a second function of also uncoupling the tiles from the substrate, protecting the finished surface from damage caused by movement.
The damage caused by water ingress into the fabric of the building can be extensive. Schlüter was recently investigating a problem at a private house where water was dripping heavily from a first-floor shower cubicle into a garage below, every time the power shower was used.
The sealant between the shower base and tiled wall was leaking, meaning water was finding its way to the room below. It’s discoloured the plaster on the garage ceiling and wall -- no real problem in a garage -- but what if it had been a lounge? A correctly installed waterproofing membrane prevents this damage.
Anyone, whether a private householder or a business, who has suffered water damage because of the lack of waterproofing would readily agree that prevention is better than the cure.
There are alternatives to using impervious membranes. Other forms of waterproofing include brush-applied liquid. 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
Go on the top
TIPS ON INSTALLING WATERPROOFING FOR WALLS
If you use a polyethylene sheet with an anchoring fleece, such as Schlüter®-KERDI – a type of impervious membrane as recommended by BSI – 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, sticking additional strips down with a 5cm overlap, securing the joins with a waterproof sealing band. Special sections are available for internal and external corners.
If you use a polyethylene sheet with an anchoring fleece, such as Schlüter®-KERDI – a type of impervious membrane as recommended by BSI – 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, sticking additional strips down with a 5cm overlap, securing the joins with a waterproof sealing band. Special sections are available for internal and external corners.
The tiles should then be solidly embedded on the front side of the membrane using hydraulic tile adhesive.
Waterproofing both the walls and floors is a must in bathrooms and wetrooms nowadays. However, there’s another consideration for floors -- not only do the tiles need to be waterproof, they must also be protected against movement. Otherwise they could crack or become debonded from the substrate.
Because the sheet used on walls is purely to waterproof, it is equipped with an anchoring fleece on both sides. Therefore it is mainly used for wall tiling, and is also ideal for protecting surfaces such as renders, plasters, plasterboard and mature screed.
But to protect floor tiles from movement -- by uncoupling them from the substrate -- as well as ensuring they’re waterproof, it would be better to look at alternative solutions.
While there are types of brush-applied liquid which offer a degree of waterproofing protection, the British Standards Institution recommends 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 material should be impervious...and be sufficiently flexible and strong enough to resist movement in the structure, and loads, without rupturing.”
A universal underlayment such as Schlüter®-DITRA which is a polyethylene sheet with the anchoring fleece laminated just to the underside, serves as a waterproofing layer, as well as protecting the tiles against movement. In order to protect the tiles from movement its upper surface consists of a grid structure of square cavities which allow any stresses that occur between the substrate and the tiles to be neutralised evenly, in all directions.
Go on the top
INSTALLATION TECHNIQUES
In a nutshell, 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 latex modified 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. Again, Schlüter®-KERDI-COLL should be used to adhere any required sealing band onto the Schlüter®-DITRA. The tiles can be laid on top immediately afterwards, by anchoring the adhesive into the square cavities.
Go on the top
