A homeowner’s new tiled floor quickly failed, exposing crucial mistakes in
underfloor heating and installation methods. Richard Renouf has the story…

THE grout between ceramic floor and wall tiles is not just for decoration. Like all building materials, tiles, and the surfaces on which they are bonded, can be affected by expansion and contraction, so it is important to have a flexible grout that can accommodate this movement and prevent the tiles from cracking.

Mrs L contacted me to ask if it was normal for grout to fall out between her newly-laid floor tiles. After a brief discussion on the phone it was clear that there was a problem that needed investigating, so she commissioned me to visit to inspect the tiled floor.

The tiling had been fitted by a plumbing company which had moved into underfloor heating and claimed it as a specialism.

They’d used expanded polystyrene UFH panels laid over the existing cementitious screed and then, once the heating had been commissioned, had laid the ceramic floor tiles over a decoupling mat. When problems had developed they had sent their tilers back and they’d tried to do some remedial work without success and eventually they had decided nothing was bad enough to warrant a complaint and so they had gone away and were not responding to the homeowner’s queries at all.

That also meant they were not willing to provide any details about the UFH system and the adhesives and other products used to complete the tiling project, information which would have been extremely helpful.

The property was a two and a half hour drive away and as soon as the customer opened the door the failure of the grout was obvious down the hallway. There were seventy square metres of tiles and the grout was cracking everywhere, and in some places had broken out.

There were many hairline cracks along the tile edges and the floor was noticeably ‘giving’ under foot and one tile around a door frame rocked if you trod on one corner. This, not surprisingly, was one of the tiles that had been treated to ‘remedial work’.

It was fortuitous that after the job had been completed, an area of tiles had been lifted inside the front door to create a mat well – of sorts. At least it was enough to enable me to look at the UFH panels and a decoupling mat that has been used over the UFH and to which the tiles had been bonded.

The adhesive bed between the tiles and the mat was very good, but the decoupling mat peeled up from the UFH very easily.

The customer had taken a lot of photographs during the project so I spent quite a while browsing through them on the customer’s phone. There was no indication of how the decoupling mat was fixed and I couldn’t be certain that the empty cans of DIY spray adhesive that were lying around after the decoupling mat’s installation were what had been used to fix the mat, but the mat itself was clearly branded and so I was able to look up the full details and instructions for its installation.

There were two basic requirements: the mat had to be fitted onto a load-bearing surface and it was to be bonded to that surface using tile adhesive. This was repeated throughout the data sheet, so it must be important.

It was obvious the apparent softness of the floor was due to the softness of the UFH panels and this was causing the tiles to move underfoot which in turn was cracking the grout. Whether the use of a tile adhesive to fix the decoupling mat would’ve created enough rigidity to support the tiles was not clear, and without the specification for the UFH the manufacturer’s recommendations couldn’t be consulted. But the movement was not helped by the poor bond of the decoupling mat which is designed to create a flexible layer between the subfloor and the tiles which resists differential movement within the floor while holding the tiles securely.

Here, the tiles were essentially fitted as a ‘floating floor’ on a flexible mat with no rigid support beneath them. Even without the full product specification, the reasons for the failure were clear, although the specifications would have added further weight to the conclusions.

Flooring products and materials have advanced significantly in recent years and it is important to keep abreast of new developments. CFJ is a great source of industry news and the Harrogate flooring show gives contractors the chance to browse and learn what’s new.

But, of course, the most basic way to avoid pitfalls is to read the instructions.

www.richard-renouf.com
Richard Renouf is an independent flooring consultant