Richard Renouf found that his feet, with shoes off, provided the perfect pointer to why an end-user wasn’t too happy with his flooring installation.

BOOTS. Really useful on a mountain as they absorb the unevenness of a rocky path and prevent your ankle twisting as you climb from rock to rock. My next call would be in North Wales, so the walking boots were in the boot in case time allowed a little excursion.

But first there was a little matter of some SPC flooring which had been laid during the refurbishment of a traditional property in a rural part of Merseyside. The size and shape of the tiles allowed it to be fitted in a herringbone pattern but the end-user had complained before the job was finished because the tiles had uneven gaps and this was not acceptable.

He’d stopped the installation before the first room had been completed. Interestingly, the installers had taken all the remaining packs of flooring away with them when they left.

I was still wearing normal shoes when I met the homeowner, but the laces were undone and the shoes were slipped off as soon as I got inside. The room was full of furniture but the tiles around the skirting boards had been taken up and I could see the edges of the fitted tiles protruding from under the dust sheets.

I could also see the exposed concrete subfloor with smoothing compound on its surface. I was also able to walk through into the dining room and kitchen where installation had not begun and could see the ‘quality’ of the work done laying the smoothing compound. I could even work out the brand of boots the builder had been wearing when it was laid because the brand name and tread pattern was imprinted in the surface before the compound had fully cured.

The photographs in this article are from the job. I’d been told, as often before, that the subfloor was perfectly flat because a smoothing compound had been put down. I’d been told the same story on the previous call the same day, but when walking over the floor in my socks I could feel the lumps and bumps that revealed some basic misunderstandings that are all too common:
Smoothing compound does not flow like water. It will not magically flatten a floor to a mirror-flat finish unless it is applied correctly.

‘Self-levelling’ does not mean that if I pour the compound over here, it will self-level the floor surface over there. It means I’ll have a lump over here with a lovely flat top and with ridges and flow marks all round the edges.

Applying compound over a small area at a time, working across the floor area will very likely give me a surface which follows the contours of any unevenness below. If I want to raise low spots to make the area more even, I have to know where the high spots are and plan to apply the compound taking this into account.

Using the wrong kind of mixing tool will trap bubbles in the compound which will rise to the surface and burst leaving pock-marks. Walking on it before it has fully cured is bad for the floor, bad for your footwear, and probably not welcome on the adjacent floor areas as well.

Usually the subfloor is not visible when I carry out an inspection but the irregularities can be detected using a laser floor scanner or even a 300mm straight edge laid across the joints between the tiles.
The location of cracks or ‘pimples (where a spike or piece of grit has burst through a tile) is an obvious place to check, but a call the day before this one had a crack right across the flooring between a breakfast bar and the opposite wall where a wall had been taken out and the floor had not been raised to the same level and a few months ago there was a crack which revealed where the electrician had channelled the subfloor for some cables.

The flatness of a subfloor is known as its ‘surface regularity’. In all the British Standards for flooring the requirement is for ‘SR1’, which means there’ll be no gaps bigger than 3mm underneath a 2m straight edge resting on the subfloor surface. Lower grades, SR2 and Sr3, are generally not relevant for flooring, but some flooring types require an even flatter floor than SR1 and the SPC I had gone to look at was one of these. The instructions said the subfloor must be flat to within 5mm over 3 metres and 1mm over 20cm.

It doesn’t sound much different, but in practice it’s a much greater demand and it’s because SPC (often called rigid LVT) is very brittle because of the stone fillers used in the backing and will crack under the weight of a user over any unevenness that exceeds this limit.

The customer was right. This flooring would be cracked within a few days at most. It needed to be uplifted so the subfloor could be correctly prepared.

I put my shoes back on as I left the house. Time didn’t allow me to use my walking boots on this trip, but their advantage on a mountain was probably the very reason why the builder couldn’t understand that there was a problem with his floor.
www.richard-renouf.com