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Commercial Flooring News

Hygrometer Refutes Installer’s Guesses

John Alcock on monitoring moisure and surface laitance

A RECENT support job dealt with by my Bostik colleague James Rosher highlighted the importance of carefully monitoring moisture during flooring work.

This might seem like second nature to many CFJ readers, but you may well be surprised at the number of calls we receive over this kind of mistake.

James was called to a site to inspect the bubbling of some vinyl floorcoverings in a bathroom area.
The subfloor was a standard anhydrite screed laid about three months previously, although the situation had been complicated by the presence of underfloor heating, which had been fully commissioned, beginning around a week after the screed had been laid.

The floorcovering had been laid to spec – about four weeks after the screed and with a two-part
primer and a floor levelling compound – and from there vinyl had been fitted with the relevant adhesive product.
However, the floor had star ted bubbling soon after, and the inspection revealed two dinner plate sized bubbles. Upon peeling away a small piece of the vinyl near to the doorway, it was clear the smoothing compound had cracked and was separating from the subfloor.

The underside of the smoothing compound was covered with a dusty residue. When the floor was tested with a Protimeter MMS2 in Pin mode it indicated a high level of moisture within the smoothing compound.

From his findings James had questions to ask the contractor regarding his preparation of the subfloor prior to star ting the job. The contractor felt that as the under floor heating had been switched on this would dr y the floor to an acceptable level. When asked if he’d tested the screed for moisture before fitting the floor, he replied that he had not felt he needed to because experience had told him it was fine to work on.

Questioned on the preparation of the surface, the contractor answered that it was swept to remove any dust but not abraded as anhydrite screeds do not have surface laitance.

But this is not always the case as anhydrite screeds do vary. In fact, dust was found on the underside of the lifting smoothing compound, confirming that sur face laitance was present and was acting as an adhesion barrier to the primer and smoothing compound used.

In shor t, although the contractor felt that there was no problem with his installation or preparation, the combination of the high moisture levels and the surface laitance meant that this floor was bound to fail.
The main point here is that it can be easy to assume from sight and experience that a floor is ready to work on, yet for a relatively small investment in a hygrometer / moisture meter, you can be sure that is the case. This in turn can help to avoid the hassle and expense of return visits, and potentially the cost of work to put the

problem right.

John Alcock is technical specifications manager at Bostik I

I T: 01785 272727

This article has been reproduced from the Contract Flooring Journal website. You can find them at