Installation with under-floor heating
General
Multi Top Floor XL® flooring is among the most stable wooden floor products on the market, and is therefore very suitable for use with under-floor heating (UFH).
However, to obtain the best performance of your floor in the long term it is important to follow these guidelines. As there is no reliable way of recording or monitoring the heating-system settings and room conditions over time, it would be impossible to prove or disprove whether all the guidelines had been followed; therefore, we cannot give a guarantee.
Make sure the UFH system is installed, fully working and tested before installing your Multi Top Floor XL® floor; you risk causing irreversible damage if you cannot fully control the system and do not restrict the operating temperature according to the guidelines below.
In practice, Multi Top Floor XL® flooring is almost certain to shrink when used with UFH, and there will be some movement of the floor. This is due to the relatively high moisture content; the solid-wood wearlayer is about 10% and the ply core about 14% when the planks come out of the factory, and these levels cannot be reduced in advance through re-kilning, for example, without affecting the integrity of the plywood.
After a month's use with UFH, these levels can drop to 6-7%; this loss of moisture manifests itself as shrinkage. If the moisture loss is severe, there can also be a breakdown in the cellular structure of the wood, leading to splits in the wear-layer.
For maximum satisfaction, these effects need to be minimised and we recommend:
The manufacturers preferred method of under floor heating is water / piped systems rather than electric mats or film.
Manufactureres recommend that board widths do not exceed 200mm wide and where possible, each individual plank should be fixed in place, either stuck or secret-nailed/screwed.
If planks are loose-laid there will be an accumulation of shrinkage in one place, which may mean a gap of 1cm or more somewhere in the floor. Instead, the effect of shrinkage will be limited to about 0.5mm on each plank.
If floated as a raft - boards stuck together, but not fixed down - the whole floor may move in an unpredictable way, especially if the room is irregularly shaped.
Some species are more suitable for use with UFH than others - merbau, walnut and oak are particularly stable. On the other hand, the more "lively" species - hard, brittle woods, such as maple, jatoba and larch - tend to react by splitting and moving more readily. We recommend these species are not used with UFH.
Wood should be sealed as soon as possible after laying. Oiled floors should be fed and maintained more often than conventional, non-UFH floors.
The use of standard, micro-bevelled planks will minimise the visual impact of shrinkage. A square-edge board will show up the shrinkage much more through slight gapping.
Installation on a screed-based system:
The screed must dry naturally to below 4% moisture content - the under- floor heating should not be turned on before the correct moisture level is achieved.
The screed must be level to ±3mm over 3m.
A PU-based adhesive, such as Thomsit P625 or similar, should be used, and will act as both adhesive and moisture barrier.
After fitting, the flooring adhesive should be allowed to cure for 2 days before the heating is turned on.
For all types:
The maximum temperature at the underside of the wood should be 26°C.
Relative atmospheric humidity should be maintained between 40-60% - using a humidifier or climate control if necessary.
The heating should initially be turned on at the ambient temperature.
It should then be raised by no more than 1°C per day until the required temperature is reached.
The room temperature should be maintained between 20°C-23°C.
The heating system should be run in strict accordance with the manufacturers' instructions.
Beware of leaving solid furniture and/or heavy rugs in one position for any length of time. If the floor is "capped" in this way, the wood may be affected by excessive heat, which cannot escape normally. This will lead to cupping and gapping, from which the floor may not be able to recover.
Electric mats or film
When used with an electric mat or film systems, there may be no way of fixing the individual planks. In this case, the loose-laid floor can be cramped up after a month or so, in order to take out any shrinkage. Care must be taken, however, to prevent the sudden ingress of humidity, which may cause re-expansion of the floor, when, for example, windows are thrown open on a warm spring day.
Please refer to us in case of further questions.
