Technical Information
Site Conditions
Whatever wood floor you are fitting the same general rules apply. The sub floor should be clean, dry, even and sound. The property into which the floor is being fitted should also be in a habitable condition, i.e. the heating, ventilation and air-conditioning systems, if applicable, should be operational. The doors and windows should all be in place, as should the roof. All wet works should have been completed and allowed to dry out fully. That is, all plastering and concreting. N.B. A general rule of thumb for concrete drying times is for every 1” (25mm) depth of concrete, 1 month’s drying time should be allowed. In other words if the surface screed is 3” (75mm) thick then it should be left for 3 months to dry out before putting a wooden floor on top of it, unless you plan to use a special underlay system.
Taking these basic points one at a time:
Clean…
There should be no dust, drops of paint or plaster on the sub floor, especially if you are planning to use an adhesive to stick the wooden floor down.
Dry…
The sub floor, if it is concrete, should have no more than 5% Moisture Content within it. This can be measured by a hygrometer or specialised moisture-testing equipment, which any competent wood floor fitter should carry. If the sub floor is to be of timber, whether this be joists, plywood or even in some cases chipboard, then this timber must not vary more than +/- 5% from the moisture content of the wooden floor that is to go on top of it. Again this can be measured very simply with a pronged timber moisture tester.
Even…
A wood floor can be laid on a completely sloping sub floor as long as it is even. Undulations within the sub floor will be reflected in the surface floor and this will cause problems in time. A wood floor may even accentuate any unevenness within the sub floor. The general rule for flooring is that if you put a 3 metre straight edge across the floor there should be no more than +/- 3mm of undulation anywhere along that 3m length. If there is more than a 3mm gap underneath the straight edge then the floor will need to be levelled before fitting your new floor. If there is a rise of more than 3mm anywhere then this will have to be reduced.
Sound…
The base onto which the new wood floor is to be laid should be completely sound, e.g. no flaking or blown concrete, no loose floorboards, creaking timber substructures need to be rectified before the new floor goes on top, no voids, etc.
Under Floor Heating
There are a number of different types of systems available and really the type of system one uses is irrelevant as to whether the wood floor can be put over the top of it. If a wooden floor can be laid over a water based pipe system, equally it can be laid over an electric matting system and vice versa.
The important things to note are:
- The moisture content of the timber.
- How it was dried and
- What type of construction the board is.
Timber moisture content…
Floorboards are usually dried out to between 8-10% moisture content. In the case of timber for use over under floor heating it should really be 6-8%. The drier it is to start with the less initial movement there will be when the heating first goes on. Gapping is almost inevitable in the wintertime, but nothing to be worried about.
Drying methods…
There really are only two methods of drying timber; the old traditional way of air-drying (curing) and the more modern kiln drying. Kiln drying is much faster and more accurate but air-drying, whilst much slower and therefore more costly, produces the most stable timber, ideal for use over under floor heating. Sometimes a combination is used of first air-drying over a period of many months, if not years and then finishing in a kiln, for uniformity.
Type of Board
There are three main choices on the market today, when it comes to buying a hardwood floor.
First is a Solid Wood floor, which is a single piece of timber from top to bottom. This will always be one single piece of timber cut from the tree. The sawing method used will greatly affect the timber’s appearance. This is the most durable and has the advantage of being thick enough to sand and refinish over and over again. It is the least stable of the three options. But, given the right preparation, can be used almost anywhere. Usually this would be secret nailed to a timber sub-structure (plywood or joists).
Secondly, and this is probably the most common option, a Floating Wood floor. This is a multi-layered timber product where only the surface layer is the timber that one is expecting to walk on. Underneath that is a further two or sometimes four layers of a different, cheaper timber (usually pine/spruce) laid cross-grain to each other. Each layer bracing the movement of it’s neighbour. Each board is laid by gluing or locking the tongue and groove together, without fixing it down to the sub floor in any way, hence the term floating floor.
Finally, there is the Engineered Wood floor, which rather like the floating floor is made up of a number of different layers of wood, cross-plied together, but this time each layer is of the same type of timber. The board in this case is glued to the sub floor, rather like a tiled floor would be. It is always best to follow the manufacturer’s guidance on installation, whichever type of board one is using, and that is especially so with installations over under floor heating.
Acclimatisation and Installation
Always find a qualified, professional wood floor fitter who has years of experience and a number of satisfied customers who will vouch for his/her workmanship. The difference between a good wood floor fitter and someone who lays all types of flooring is that the former will add quality to your floor, whereas the latter will simply lay your floor. But a wood floor is something that is being fitted for a much longer period than a carpet or vinyl floor and therefore much more preparation and care needs to be put into the process, not to mention attention to detail.
Every manufacturer has their own specific rules regarding the installation of their floor. Check to make sure your installer is familiar with the product you have selected. N.B. Not all floating floors are laid the same. This is also true of solid wood floors and engineered floors. If you are not sure there are a number of professional bodies that can advise. We also have a help-line for advice and assistance. See our contacts page.
Acclimatisation is something that varies according to the type of floor selected and the manufacturer’s particular rules, but in most cases if the timber needs to be acclimatised, then please allow at least two weeks for this prior to installation. This period allows the timber to adjust to its new environment BEFORE it is laid!
Furthermore the timber needs to acclimatise in the room in which it is due to be laid. It is no good allowing it to be stacked in a garage or outbuilding for two weeks prior to installation, only to bring it into the room into which it is to be fitted on the first fitting day. It will then adjust to, potentially, this completely different environment after fitting, which is best avoided.
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