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Do you have a gap in your knowledge when it comes to floating floors?

It’s essential any product to be fitted as a floating floor must have a minimum expansion gap around the perimeter which will vary according to the product type. Richard Renouf advises.

ALL building products will naturally expand and contract with changes in ambient conditions. Wood (including engineered wood and laminates) is mainly affected by changes in relative humidity and LVT and SPC flooring is mainly affected by changes in ambient temperature, although there’s some overlap as relative humidity is affected by temperature (I dealt with relative humidity in detail in a past issue of CFJ which can be accessed on the CFJ website).

To accommodate this natural expansion and contraction – which affects the building as well as the flooring – it’s essential the manufacturer’s instructions are followed, and any product to be fitted as a floating floor must have a minimum expansion gap all around the perimeter which will vary according to the product type: for SPCs this may be as little as 2mm, for LVTs it’s more likely to be about 6mm and for laminates, engineered and solid wood it will be in the region of 10-15mm depending on the product and manufacturer.

The flooring must also not be fixed down in any way by fixtures such as kitchen units or stone hearth slabs underneath wood-burning stoves, etc.

Although this is basic knowledge to most readers of CFJ, the results of restricting a floating floor are not so obvious and in many cases the results are taken to be faults with the flooring and the connection with the installation isn’t made by the installer.

It’s also not always easy to explain when someone wants a blow-by-blow account of why there’s a gap here and a chip there that seem to be away from the restrictions.

A quick calculation tells me I’ve inspected more than 1,500 failed floating floors. In my experience there are three types of restriction that can affect a floating floor, and the results of these are logical and predictable if you take the time to think them through.

The first issue is caused when the flooring is fitted without any expansion gap or with too small an expansion gap. When close-fitted, any expansion of the flooring will cause it to lift as soon as it’s tight at any point around the perimeter. If the gap is too small, this may only happen in more extreme changes in ambient conditions. It only needs two ‘pinch points’ where the flooring is against the wall or another obstacle for the flooring to lift.

The best illustration of this is in your hands (if you’re reading the printed edition of CFJ). If you lay the open magazine flat on a desk or table and then put one finger at the top of the page and a finger of the other hand at the bottom and slide one finger (with the page) about a millimetre towards the other, the whole page will ripple, not just the area between your fingers, the pinch points.

Once lifted, the paper can be pushed and prodded and it will simply move the ripple around the page. In practice, when flooring lifts like these it may only be half a millimetre, but it’s enough to cause the joints to flex underfoot and this in turn will cause damage to the joints.

In almost every case it’s the header joints which are damaged first. This is because there are fewer of them per metre and they are smaller so cannot take the same pressure as the joints along the rows. The damage that results is usually visible because the joints will become uneven (lipping) and on laminate flooring the wearlayer will chip easily. In more extreme cases the joints can peak and curl upwards, with LVT tiles showing distinct crease lines parallel to the header joints.

A second issue is where the flooring is fixed down in some way. It is quite common for a floating floor to fail because a fitted kitchen or island has been fitted on top of it, or the flooring has been fitted underneath the front feet at least. It might also be that a wood-burner has been fitted after the flooring, or a doorstop or floor socket has been fixed through it into the subfloor.

Fixed points will cause the flooring to lift when it expands, but they will also cause the joints to be pulled apart when it contracts. This can result on the joint profiles breaking and the headers coming completely apart. Gapping like this, however, can be less predictable because the joints will fail where the friction is lowest and this may be well away from the area under tension. With LBVT floors tension can also cause creasing and opening along the header joints.

But a fixed point may not be quite so obvious. I’ve seen a lot of installations where the installer has not fitted the kitchen onto the flooring but has cut the flooring tightly around features such as décor end panels. Where this happens along a run of units, the flooring between these ‘hooks’ cannot expand or contract. If the kitchen is ‘L’ or ‘U’ shaped, this can create complex forces that damage the joints easily and permanently.

Another fixed point can be created by using incorrect door bars and edge trims. Screwed down cover plates trap the edge of a floating floor and prevent movement.

The third most common issue I come across is the use of sealant around the perimeter of a room. Sealant is actually a very strong adhesive and although it may be described as ‘flexible’ on the tube, when it’s applied at the bottom of a skirting board it will prevent the flooring from sliding to and fro during expansion and contraction.

It’s quite common in these circumstances to find the skirting board is actually being pushed in at the bottom and so is opening up along the top edge. It’s also common to see the sealant coming away and leaving a gap of several millimetres where the flooring contracts.

Combine more than one of these issues and the results can be dramatic. Gapping and lifting in the same area, external door frames being pushed outwards, entire rows separating, or lines of header joints breaking upwards where the flooring has been laid in brick-bond fashion (which, it must be said, isn’t good practice).

One final reflection: although a floating floor acts as one whole unit where it can, some restrictions can force boards to slide in relation to each other when expanding or contracting but the joints may not return when the flooring moves in the opposite way.

The next period of expansion then causes the joints to move further apart, and again they don’t close up when conditions change. This can create a ‘ratchet’ effect which separates the joints completely over a period of time.

There are other reasons why joints may get damaged or may open up, so the presence of compression damage or gaps may be the result of other factors, but check how the flooring is fitted and it should be easy to work out.
Richard Renouf is an independent flooring consultant

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