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Expansion and contraction part 2

WITH this article coming after the Christmas and New Year holidays, you’d be forgiven for thinking this is going to be another about expanding waistlines and what to do about it. But no, this is my first technical article for 2020 which will hopefully highlight that expansion, and the need to consider it, is a recurring theme in flooring. What I’ll try to do is cover the most common expansion topics to hopefully give a useful overview.

Expansion is a natural phenomenon in both buildings and products. It can be best described as the increase in the dimensions of a body or substance when subjected to an increase in temperature. It’s diametrically opposite to contraction which is where dimensions reduce owing to cooler conditions. Expansion and contraction are important considerations when installing flooring, particularly with the current trend and increased availability of loose-lay products or systems.

Back in February 2018, I wrote an article in CFJ centred on acclimatisation that mentioned expansion and contraction of flooring:

So, correct site and product temperature really does go hand-in-hand with acclimatisation – get these right and together they will allow the flooring to relax and take up its correct size (many products will contract when cold and expand when warm). Failure to do so may end up in failure of the floor installation.

It’s expansion which provides the biggest headache onsite, often revealing itself post-installation, usually when the building is heated or sunlight streams in through large south-facing windows. By contrast, cooler temperatures will result in gaps appearing between product sections or around walls. Expansion in products can cause lipping or lifting of floor sections which, in extreme cases, can present a trip and health and safety issue.

Back to acclimatisation, all products need to be acclimatised to the standard 18-27deg C stated in British Standards or, by exception, to the expected conditions for normal use in the building/room. Failure to work to this temperature range (including before, during and after fitting) will open the product and installation to possible movement. While expansion is a headache onsite and can cause lots of issues, contraction is probably one of the most common aesthetic complaints that modular product manufacturers receive. An otherwise acceptable floor becoming entirely unacceptable to a client owing to gaps between tile joints.

Manufacturers and suppliers will provide information on typical expansion figures for their products and clear guidance as to fitting requirements. If any doubt exists before fitting, always refer to the manufacturer/supplier for guidance.

For products that are liable to expand/contract in use, allowance needs to be made in the form of expansion gaps around the product perimeter and sometimes in the body of the floor to facilitate any movement due to temperature changes. This is common with loose-lay products and an essential gap that must be left around the edge of the room when fitting for example, hardwood, bamboo or laminate flooring.

The expansion gap should be around the whole perimeter of the room, wherever the flooring may be against fixed objects, such as walls, doorways, radiator pipes and fireplaces. As with train stations, the gap between the train and platform is designed in for a good reason.

As wood is a natural product, wood and wood-based floors will absorb excess moisture in the air caused by humidity with the resultant expansion of planks of flooring. Then, as the levels of humidity in the room are reduced, the planks of flooring will contract again. An expansion gap around the edge of a room will allow for natural expansion and contraction into the gap without causing any damage or distortion to the flooring itself.

If no expansion gap has been left, when a floor naturally expands it will have nowhere to go and will lift-up and damage the flooring and, in the worst-case scenario, even push walls out and damage the structure of a building.

Vinyl (classed as an elastic product) is susceptible to temperature changes in its ambient environment which will cause the vinyl flooring to expand and contract with normal hot and cold fluctuations. When installing floating vinyl flooring it’s also necessary to allow for this expansion by leaving a gap around the perimeter of the floor or anywhere it meets another floor or vertical surface.

We usually think of gaps as a bad thing. But when properly used, expansion gaps can relieve the pressure from heat expansion that can affect a floating floor before it meets an immovable, vertical obstruction. Such close encounters between the floor and a wall, for example, can result in a noticeable and unsightly buckling or peaked appearance.

Expansion gaps will vary for each product type and range from 1mm to 15mm or greater, so care needs to be taken to check the actual requirement. Just guessing is not sensible or scientific when it comes to expansion. To ensure the correct sized expansion gap is left, flooring spacers can be used during installation which are removed once the installation process is complete.

But it’s not just the flooring product that can expand, wooden substrates (especially floating systems) can also be affected in the same way as wood flooring by changes in humidity. When fitting to timber based substrates, it’s important to check the conditions in which the boards were stored and fitted. This is particularly true of new build houses.

At a recent CFA manufacturers’ committee meeting, Ian Rochester, technical affairs manager, Wood Panel Industries Federation, listed some simple checks that can be carried out prior to fitting flooring:

  • Try to determine how conditioned the floating floor is:
  • Take moisture readings of the panel and other pieces of wood in the room
  • Get an idea of how ‘wet’ the room is
  • Find out how long the floor has been down
  • How long unoccupied/occupied, how long ago were wet trades were working, has heating been on?
  • If you suspect an issue, advise what needs to be done before the floor is laid to bring as close to ‘in use’ conditions as possible
  • Look for expansion and movement gaps at the edge of the room
  • Look for intermediate expansion gaps in long runs

The mention of wet trades is important as, for example, plastering can introduce large amounts of moisture to the building which in turn can adversely affect the stability of any wood or wood-based product.
While mentioning wood, it’s also possible for movement within stud partition walls and floor joists owing to humidity changes from a building site to a fully occupied and heated space. This usually takes the form of shrinkage, as the wood dries out, revealed by perimeter gaps around flooring installations or rippling/lifting of sheet or tile installations. Basically, the original subfloor, once dry and contracted, is now smaller than the flooring fitted to it.

I remember going to a newbuild house where the builder was complaining that the vinyl sheet flooring in the first-floor bathroom was rippling. After asking some of the questions above, I discovered the house was built to the first-floor level, then the floating chipboard floor fitted before a roof or covering, and all this in mid-winter!

Although explaining that the subfloor had moved (contracted) with heat when turned on, the builder wasn’t happy. We then went into one of the bedrooms where carpet had been fitted – the builder said: ‘Look this is OK.’ Lifting an edge of the carpet revealed two things:

  • A large vertical gap between the chipboard floor and the skirting (where the joists had shrunk)
  • More interesting, a very skilful paint job. The painter had manged to paint the skirting and a thin line on the floor away but parallel to the skirting. I couldn’t help myself, saying: ‘Interesting, you must get me his contact details,’ as I looked up at the builder. Enough said. The builder admitted defeat and we left for a cuppa in his office.

From a contract product perspective, I have experience of a carpet tile installation where the tiles had dished across the floor. The customer complained the tiles were faulty. It turned out that the tiles had been transported during the winter on a cold truck and fitted without being acclimatised into a cold site. Once the heating was turned on, the tiles naturally expanded. The sideways pressure, in all directions, caused the tiles to ‘dish’ or become deformed. That doesn’t mean there was a product fault, rather a classic case of product expansion owing to lack of acclimatisation. There was just not enough floor space for the expanded tiles to lay flat.

Sunlight can create differential expansion issues with flooring particularly in south facing sides to buildings with floor to ceiling glazing or conservatory type buildings. The floor temperature can increase exponentially (most commonly reaching 40deg C or higher) where the sun hits the floor with subsequent expansion pressures in the floor. It’s common in LVT installations for manufacturers to recommend the use of high temperature adhesives or two-part PU adhesives to ‘fix the tiles’ to prevent them from moving.

Of course, this isn’t only to manage expansion and contraction as in extreme conditions (south-facing patio doors, no curtains) high temperature can cause the product to be over-annealed, releasing internal stresses caused during manufacturing and thus also causing gapping. This isn’t expansion or contraction in its pure form as the structure of the product has been modified. The adhesive is restraining the product and stopping it from becoming damaged.

Another product area requiring a suitable expansion gap is rigid entrance flooring systems. These products are loose-lay into matwells (recessed or surface ramp type frames) and, as they’re usually in doorways, the need to allow expansion is paramount. I’ve seen incorrectly fitted products expand and dome (lift off the floor) to the extent the door catches on the surface or cannot even open, both becoming health and safety issues.

Manufacturers will make custom-sized product orders with an expansion tolerance built into the product dimensions. Importantly, when fitting and shaping products onsite, the same expansion tolerance must be adhered to.

It’s also important to understand how certain products behave when being fitted. Linoleum sheet is one such product that, while dimensionally stable once fully bonded to the subfloor, will experience contraction and expansion before and during fitting. Back-rolling of linoleum is recommended to release any tension in the product between the hessian backing and the linoleum surface. When you back-roll linoleum, the product will shrink a little in the length. If you don’t back-roll, the product is likely to shrink during fitting with gaps appearing at the ends.

Also, when the sheet linoleum is placed into the wet adhesive, the product will expand very slightly in the width. This explains why, when fitting adjoining sheets, it’s advised to leave a wafer-thin gap to allow the sheet to expand slightly to avoid a peaking seam.

Lastly, solid subfloors have expansion joints built into the design as concrete and similar substrates will move with thermal changes. A common question is: ‘Can we fit the flooring over/across these expansion gaps?’ The answer is no, if they are structural expansion joints. They’re in the subfloor for a reason and need to perform the task they are designed to do, namely allow the subfloor to move freely. There are proprietary expansion joint cover profiles specifically designed to allow the subfloor to move freely without damage to the flooring either side.

Fitting directly over subfloor expansion gaps will cause the floor to either split (contraction of subfloor) or ripple (expansion of subfloor). Either way, a problem that can be easily avoided by retaining the integrity of the expansion gap.

In closing, always refer to manufacturer/supplier installation guides and standard documentation such as the CFA Guide to Contract Flooring, before commencing the fitting of any floor. Even similar type products can require different handling or have unique fitting requirements.

This is especially true of loose-lay products requiring a minimum expansion gap tolerance. It’s better to check first than encounter a major problem.

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