Sometimes, says Richard, problems with a particular type of flooring can come in waves for no obvious reason. Recently, the problem has been underlays…

SOMETIMES complaints come in waves. This would be expected if, for example, a faulty batch of a product had been distributed and so there were a lot of similar issues. But sometimes it just happens for no discernible reason.

For the past few weeks, the common issue has been underlay. It started with an inspection of some laminate flooring which was coming apart at the joints and when I investigated, I found it had been fitted straight over the customer’s old carpet.

Then I had a series of calls to failed click-LVT flooring. Some were the usual problems with expansion gaps or silicone sealant, but there were three for which laminate underlay had been supplied. In each case there was either an excuse from the retailer (‘The LVT underlay was out of stock so we sent what we had’) or there was a lack of knowledge (‘It’s the same stuff, isn’t it?’). But there was also significant damage to the flooring: it looked bad because the joints were separating and breaking, and the damage was widespread.

Then another laminate problem was perplexing me. Two header joints on adjacent rows had come apart close to the back door of a kitchen, with the doorway through to the utility room close by. The joints didn’t seem broken, and other joints in the utility room which had previously come apart had been ‘kicked’ back together by the customer and appeared to be holding.

I went through my inspection routine and took of a kitchen unit plinth to check the subfloor (or to see if the flooring was fitted underneath the units, which isn’t a good idea). It looked as if there was a lot of sawdust, but when I reached down, it was the customer’s old kitchen carpet which hadn’t been uplifted.

The boards had been forced open by the softness of the carpet combined with the ‘ratcheting’ action of the pile which pushed the boards one way but resisted any movement back.

Yesterday was another variation on the theme. I’d asked the retailer who instructed me to confirm what the flooring and underlay were. They gave me a copy of the invoice to confirm what had been ordered and supplied. The flooring was laminate, and the underlay was an expanded foam 5mm thick and a black colour, recommended specifically for laminate flooring, and a product I was familiar with.

When I got to site the flooring was a mess. There was extensive damage along the joint lines, and in the hallway the joints had failed completely, with wide bands of exposed core material around all the joints, and some end joints opening up allowing the boards to slide into the kitchen where the doorbar had been removed.

Alarming as it was for the customer, this was a great help to me as it exposed the underlay. A soft white felt, discoloured, and ingrained with dirt and debris where the gapping had been occurring, but clearly very different to the underlay I’d been told to expect. I lifted the edge of the boards in the doorway and there was no sign of the black foam underlay.

It’s not for me to question where the correct underlay was, or why it had been substituted. Perhaps the fitter had something he felt (forgive the pun) was suitable, or he used something that was already down to save work and had retained the unused product for another job. I can understand the temptation to do either of these, but it’s not only dishonest, it also shows a lack of understanding about the important role underlays play.

Before I recap on the benefits, let me point out, from years of looking at failed flooring, what underlays don’t do.

Underlay doesn’t make laminate or LVT flooring feel softer or more luxurious. Although this is a great selling point for carpet underlays, LVT and laminate are not intended to ‘give’ underfoot. The joint profiles are only strong enough to stop the boards separating but they cannot take the weight of a person and need to sit flat against a firm enough surface to ensure the joints stay together. This is why the density of the underlay is crucial.

Laminate has a greater inherent stiffness than LVT, with rigid (mineral-based) LVT products coming somewhere in between, and that’s why you can’t interchange the underlay from one product type to another. And it’s why in the inspection I just described, the over-soft underlay had caused such extensive damage.

Underlay doesn’t even out uneven subfloors. Whether you’re looking to bridge over a few lumps or spikes in a subfloor, an underlay is a consistent thickness and doesn’t vary in order to flatten out irregularities. It will create a floor surface the same profile as the subfloor below and only minor blemishes will be effectively hidden.

Just as important, it isn’t for filling hollows in the subfloor to try and create a flat surface. An installer in Nottingham found this out when he tried to even out a subfloor that varied by more than 40mm in height by using multiple layers of underlay – it would’ve been quicker and cheaper to use the right preparation product, even without including the cost of the new flooring that was needed because it didn’t work.

Underlay also doesn’t act as a damp-proof membrane, unless it’s specifically made to do this. Laying underlay as a substitute for taking moisture readings isn’t to be advised.

Under LVT and laminate, underlay has two principle benefits: sound and heat insulation. It helps prevent noise when using the flooring, both for the user and people in connected rooms, and it can help make the flooring feel warmer underfoot as it minimises heat loss into the subfloor. It can also cover very minor blemishes, such as very small particle of grit that got missed when the fitter vacuumed up before starting work.

And while we’re on the subject of heat insulation, this also needs to be taken into account when fitting click LVT over underfloor heating, or under or inside large areas of glass such as bi-fold doors and glazed ceilings where, because temperatures in direct sunlight can at times exceed 60degC, heat dissipating underlay should be used, and the manufacturer’s instructions should be followed.

One final thought is about fitting laminate flooring over underfloor heating. Some UFH manufacturers make underlays to go underneath electric heating mats which they claim are suitable for use directly under laminate flooring.

Not all laminate manufacturers agree, and as these underlays are sometimes too soft, they’re not universally acceptable. The manufacturer of the flooring should be consulted.