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Hardwood Flooring Fitting Advice

On site pre-delivery conditions - before the boads come on site

1) All wet trades (such as concreting, plastering, and decorating) should be finished, and the building must be throroughly dried out  (please note that plaster may take six weeks or more to dry completely) . There must be no signs of moisture or condensation and the average relative humidity shoud be in the range 45-65%. Flooring must not be laid until the relative humidity of the sub-floor is below 65%.

2) The heating should have been commissioned and operating for a minium of 2 weeks, in any event the temperature and relative humidty should be stable. Pre-finishing acclimatisation of boards on site is very important.

3) Providing that site conditions are correct before the boards arrive (see above) the boards should be shored prior to laying in warm dry conditions (similar to those which will prevail when the floor is laid and in use). Ideally they should be kept in the room where they are to be laid for two weeks or more, to allow them to acclimatise to the ambient temperature and humidty. The flooring must be well protected against damage from other building operations. Above all they must not be stored outdoors, in an outbuilding, or in a room with poor ventilation or with damp or condensation problems.

Expanion gaps on fitting -

4) When the boards are fixed, expansion gaps must be left wherever the floor meets obstructions including all walls, doorframes, thresholds, structural supports, fireplaces etc. These expansion gaps can be covered using skirting, or edge trims (e.g scotia or quadrant), or a tee-section in doorways. The expansion gap must be at least 2mm for every 1m span across the boards, with a minimum of 15mm. A tee-section can be used in doorways to increase expansion provision where several rooms run continuously. In large areas it is recommended that additional expansion provision should be allowed by the inclusion of washer or panny joints at intervals across the floor. Seasonal fitting should be taken into account. For example in centrally heated houses it tends to be drier in the winter than in the summer, so floor boards which are acclimatised and laid during the winter may expand in the summer when the heating is off. 

Laying boards over underfloor central heating -

5) The ambient humidity range between when the heating is on and off is greater than with more conventional above floor heating systems and result in greater fluctuations in the MC of the boards. It is therefore not recommended to lay boards over underfloor central heating. Contractors who wish to take this route do so at their own risk. The moisture content of existing timber is a useful guide to prevailing conditions, and can be checked using a moisture meter.

Fitting to a Sub-floor -

6) The sub-floor too must be even, with no greater than 3mm deviation over 3000mm, with no unduly high or low areas. Hot pipes should be well insulated to prevent localised hot spots under the floor, as these can lead to excessive shrinkage.

The sub-floor should be in good structural condition, dry, sound and treated with insecticide and fungicide. New timber joists, battens and supporting timber should be kiln dried to 15% and under. The mositure content of the sub-floor boards or sheets should not exceed 15%. If boards are being laid on a ground floor the underfloor cavity should be filled in with insulation. The sub-floor must also have a damp-proof membrane installed.

Fixing to timber joists: Kiln dried timbers may be fixed to joists on 1st floor level or above. On ground floor joists it is recommended that a structural (i.e load bearing) timber based sheet of material is first installed to the joist. A moisture vapour narrier building paper must then be laid over the sheet material with joins overlapped by 100mm and taped with a moisture resistant tape. (This is to protect the wood from humidty beneath the floor, which  can lead to cupping.) The joists should be 400mm centres or less and the boards should be laid 45 or 90 degrees to the joists. If there is chipboard or plywood over the joists, the boards should where possible be nailed or screwed into the joists (through the sheet material) at 400mm centres or less.

According to BS8201- boards exceeding 100mm in width cannot be secret nailed alone, but require additional adhesive which must be applied to the sub-floor (fully bonded), and/or face nails or screws.

Important note: At no time should the adhesive be applied to the long togue and groove joint.

Fixing to a concrete sub-floor -

7) Concrete screeds and slabs must be sound, dry, level, smooth, free of laitance and have no excessive localised irregularities, and must contain a damp proof membrane. Concrete takes a particulary long time to dry and should not exceed 65% relative humidity (which is approximately 3% moisiture content).

Important note: If there is any doubt that the sub-floor meets the required standard for moisture or has an effective intergral damp proof memebrane, a surface applied damp proof membrane must first be installed.

Maintenance - 

8) Always have a dust-attracting mat at enterance sites, this will prevent any sharp stones or dirt scratching the floor.

9) In a domestic situation a dust-attracting mop can be used, it will keep floors clean and dust free. Use felt pads on the feet of furniture to protect the floor from excessive scratching.

10) In a commercial location, felt pads or other forms of protection need to be used to protect from excessive scratching of the floor. Heavy scratching will break the seal of the lacquer, causing damage to the timber by ingress of dirt and moisture from cleaning.

In summary: basic rules to check

1) Sub-floor moisture content (must be 65% rh).

2) Relative humidity level in the room between 45%-65%.

3) All windows and doors to be fitted/watertight.

4) All heating/air conditioning systems commissioned and operating.

5) Sub-floor to be even as indicated ( 3mm over 3000mm)

6) Expansion gap where ever the floor meets obstructions is essential (2mm per 1m with a minimum of 15mm).

7) Timber should be acclimatized for two weeks in living conditions.

 

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