Tiling adhesives bond to subfloor in new build

Schluter Technical Manager Ian Knifton explains why problems sometimes occur and what can be done to overcome them.

A problem sometimes facing builders is that normal tiling adhesives won't always bond to the subfloor in their newly-built property.

This means that, on the face of it, their end-user customers won't be able to have tiled floors in showers, bathrooms and kitchens.

Schluter-Systems ., world market-leader in tiling solutions, was recently called in to troubleshoot when a builder needed to put tiles on the floor of a new house.

But the tile adhesive just wouldn't stick.

Schluter Technical Manager Ian Knifton explains why the problem occurs, and what can be done to overcome it.

A number of modern floorboarding materials are either specially impregnated or have a coating which resists water penetration.

This is because the floor will often be open to the elements while construction work continues, and could suffer damage from rainwater and dampness before the roof is put on.

Also, you will find that some coatings which make the floorboards fire-retardant, may have the same effect on tile adhesive.

In situations like this it could cut down on the possibility of tiling floors in areas where customers traditionally want tiles.

However, if you overboard the subfloor you will create a surface which the adhesive will stick to.

Unfortunately, this will raise the overall height of the floor by a significant amount, and will add to the cost of the tiling, but it can overcome some problem areas.

When that answer was presented to the builder, he wasn't too happy with having to pay more, and asked if there was an alternative solution available.

One solution which is proving increasingly popular in overcoming this particular difficulty is to uncouple the tiles from the problematic substrate.

The most effective and popular way of doing this is with Schluter-DITRA, a polyethylene matting with a fleece laminated to a grid-type structure of square cavities on the top.

The fleece is adhered to the substrate, and the adhesive used to bond the tiles actually anchors into the dovetailed configuration, mechanically locking the tiles on to the top.

Because you're not actually bonding the matting down with the same force that would be required for bonding tiles directly to the substrate, alternative vinyl-type adhesives can be used which will fasten it sufficiently to most types of wax coatings or impregnated sealers in the floorboarding.

Ideally, however, you would still need to seek specialist advice, because, while there is a wider range of adhesives suitable for bonding the membrane to the subfloor, not all types will be suitable.

To successfully bond the Schluter-DITRA matting, use an adhesive which is appropriate for bonding the membrane to the coated or impregnated floorboarding, as mentioned above.

Apply using a 3mm x 3mm notched trowel.

The anchoring fleece on the underside of the matting must be fully engaged in the mortar to provide a mechanical bond to the substrate.

Then, using the thin-bed method, set the tile covering directly on to the membrane, so that the tile adhesive becomes mechanically anchored to the cavities which form the top surface.

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