The worst subfloor Richard Renouf has ever come across was in a former Soviet bloc country.
But recently he inspected the worst ones he’s seen in the UK.
THE worst subfloor I ever came across was not in the UK, but was while I was doing charity work in a former Soviet bloc country where sheet vinyl had been loose laid directly onto earth. I was in one of the poorest areas of the country and few houses had concrete floors – the exceptions being the high-rise concrete blocks of flats which had other issues.
A recent inspection, however, was the worst subfloor I can remember seeing in the UK. The area concerned was part of a kitchen and utility room. This had recently been extended by removing an external wall and leaving an archway from the old to the new. Just to the left of the archway was a hump of more 30mm in an area only about a metre square, and to the far right the flooring sloped up in the corner by more than 20mm. To compound the issues, there were other visibly uneven sections which looked very much like trowel marks from poorly applied smoothing compound or uneven screed.
The customer had the original architect’s drawing and specification for the subfloor. How a builder could create such unevenness using flat insulation boards with a chipboard top surface is something I’m hoping to learn as the case unfolds. But the clue may have been hinted at by the irate builder who called me after reading my report to ask where the (bleep) I had obtained that information as the make-up had been completely changed during the build and I had clearly, in his eyes, been misinformed.
Subfloor flatness can be a contentious issue. In many cases, a flooring manufacturer will state how flat the subfloor should be for their product, and if this requirement isn’t met the manufacturer will understandably reject complaints where unevenness is likely to be contributing to the problems. Gaps in stuck-down LVT tiled flooring, breaking joints on laminate and other floating flooring products, and even cracking on rigid LVT and engineered stone products.
Where this is no manufacturer guidance, however, or the product installation instructions simply state ‘the subfloor must be flat’, what is the standard?
British Standards give three ‘grades’ of flatness. SR1 is flat to within 3mm over 2 metres and there are greater tolerances for SR2 and SR3. But the British Standards do not state which tolerance should be used for a given type of product, they simply require that this issue is discussed and agreed before the contract is finalised, and the gradings are simply a way of stating what the flatness is, not what it should be. In the present case, however, I doubt the flooring would have managed SR5 if such a standard existed.
The product instructions stated that the subfloor needed to be flat to within 5mm over 3 metres. This is much harder to achieve than SR1, even though it may not sound much different. As it was the builder who laid the flooring as well as the floor, there were no excuses for the really poor and completely unsatisfactory results.
But even if SR1 had been achieved, the trowel marks which were showing through the vinyl were not significant enough to ‘fail’ the standard. Fortunately the CFA Guide to Contract Flooring and the NICF Guide to Domestic Flooring both state that trowel marks (aka flow marks) are not acceptable if they show through the finished flooring. A self-levelling compound relies on competent installation, it does not work miracles.
www.richard-renouf.com
Richard Renouf is an independent
flooring consultant
