Temperature Changes Can Leave You Unstuck
John Alcock on adhesive selection
I RECENTLY visited a house that had been built in the 1950s; it had a modern concrete floor extension leading off from the kitchen. Problems arose after new floors had been fitted throughout the house after the extension was completed.
Luxury vinyl tiles were laid in the kitchen, but unfortunately these begun to lift shortly after they had been installed. It should be noted that a warm water underfloor heating system had been fitted as part of the extension project – but only in the new areas and the kitchen.
My first thought was whether the UFH had been commissioned properly, but the contractor assured me that it had.
As I’ve said in previous articles, the best way to ensure this sort of system is commissioned correctly is to follow CFA guidance. That states, in brief, that after allowing 21 days for cement and sand screeds and seven days for calcium sulphate, the UFH must be started by switching on the system at ambient water temperature for a period of three days.
Thereafter temperature should be raised by up to 5degC per day until the design temperature has been achieved.
After leaving the system running at this level for at least four days, the process should be reversed until the ambient temperature is reached again. From here the floor can be tested for moisture and further work done.
Because it appeared that these steps had been followed, we could rule out the UFH as the cause of the problem.
Further investigation was required, which revealed the kitchen floor to be a traditional floorboard construction with a cavity underneath. The cavity had largely been filled in with loose aggregate, with the underfloor heating pipes laid on top of these close to the floorboards.
Due to the type of finishing fitted throughout the house and including in the kitchen, the floorboards had then been covered with ply and a standard latex smoothing compound. Whilst this was suitable for most of the house since the floorboards in these areas weren’t exposed to the changes in temperature from the UFH, and therefore not liable to repeated, frequent movement. The inflexibility of the latex smoothing compound in the kitchen meant it had started to crack.
The situation had been made worse by the fact that the contractors had used a standard pressure sensitive adhesive throughout. Again, a perfectly suitable product for normal applications, but not with regular temperature changes caused by UFH, which meant it had failed to maintain adhesion to the LVTs.
The best bet for a screed in this situation – where frequent movement of the subfloor is anticipated – is a highly elastic fibre reinforced product that can best withstand movement without compromising its integrity. Selecting an adhesive designed specifically for dealing with these conditions – namely a high temperature adhesive – is the best bet for avoiding any expensive return visits.
It’s likely that the flooring contractor was under pressure to complete the job quickly, and felt that using the same screed and adhesive throughout would be good enough and help speed things along.
However, this example shows it’s always a wise idea to take into account how factors such as UFH can affect the performance even of products you may have used reliably for years, and the importance of making sure the products you eventually choose are specifically designed to be up to the job.
John Alcock is technical specifications manager at Bostik
T: 01785 272727
This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.