Wood Floor Laying Advice

Preparing to lay

The most dangerous enemy of hardwood floor is moisture. Wherever you are planning to lay your floor all other materials (concrete, plaster and timber) must be dry. The room in which the floor is to be laid must have settled to the ambient conditions of temperature and humidity that will usually prevail at that time of year.

Any timber – existing flooring, joinery or battens – should have a moisture content of no more than +2% above the moisture content of the new floor. It as advisable, when laying on to existing timber, to ensure this is treated against fungal or insect attack.

Concrete or screed should contain a damp proof membrane and have a moisture content of no more than 5%. This is, in practice, almost impossible to achieve and so additional precautions should be taken to prevent moisture reaching the new floor.

However it is worth remembering that any new concrete or screed will take approximately 1 day per mm thickness or 1 month per 25mm of thickness to dry naturally to a moisture content of 5%. The thicker the slab, the longer the period, for example a 150mm slab will probably take 10-12 months to dry back to a safe moisture level. (Please contact Millennium Hardwoods for advice on how to cut this time.)

At the time of laying the ambient conditions in the room should lie somewhere in the range of 40-50% humidity and a temperature of 15 to 25oC.

Only order the floor when you are ready to lay it. Under no circumstances store it in a room that is wet or outside, or even in a garage where it could pick up moisture.

Take the floor into the room in which it is to be laid in the optimum working conditions and allow it to adjust to the temperature etc for a minimum of 48 hours. True acclimatisation will take a few weeks and this is best done after the floor has been laid (assuming correct allowance has been made for expansion of contraction).

Allowing for expansion

All wood floors will expand and contract over the course of the year. Typically they will expand across their width during the summer as the air becomes more humid and the boards take in moisture, and shrink during the winter when heating dries out the air and removes moisture from the boards.

Kiln drying to 8-10% moisture content will minimise excessive movement.
Allowance for expansion should be left around the edge of the floor – a gap of 15-20mm is usually sufficient.

However, a floor laid in winter that will expand in the summer may require additional expansion to be allowed for across the width of the floor.

Recommended fitting methods

Millennium Hardwoods recommend that all our floors be installed by secret nailing to timber (either an existing floor or battens or plywood laid over concrete). The advantage of this method is that boards can be fitted tighter together for a better fit. In addition, the mechanical fixing of boards is a long established technique that allows the boards to expand and contract whilst remaining firmly fixed down.

Gluing directly to concrete is becoming an established method of fixing providing that the screed is completely smooth and level. Where this is seen as the preferred option we would still recommend the laying of plywood over the concrete and the floor being glued and pinned to the plywood. (Millennium stock Sika glues.)

Any board more than five times wider than it is thick is more prone to bowing and cupping. Therefore any board over 140mm wide should be nailed additionally across its width either by screwing and pelletting, face nailing or using adhesive on the back of the board.

Fitting to concrete floors

We do not recommend directly to ground floor joists as this may cause the floor to cup. This occurs typically when the air below the floor is moist and causes the underside of the board to expand whilst the air above the floor is dry (usually due to heating) causing the topside to contract.

Millennium Hardwoods would recommend the laying of 18mm exterior grade moisture resistant plywood overlaid with a non-polythene vapour barrier with the hardwood floor secret nailed to the plywood.
On second floor joists where the problem of differential moisture is unlikely to occur, the hardwood floor can be secret nailed directly to the joists (assuming they are at centres no wider than 400mm). An additional vapour barrier is not required.

Fitting to existing floors

A new solid hardwood floor can be fitted to an existing floor whether it be old floorboards, sterling board, plywood or chipboard (though chipboard does not hold a nail as other floor types).
When fitting to existing floorboards these should be well fixed down, any high points sanded out and all nails punched below the surface. On a ground floor we recommend overlaying with a non-polythene vapour barrier. The new floor is then secret nailed at 90◦ or 45◦ to the direction of the existing floor.

Where, for aesthetic reasons, it is desirable to lay the new floor in the same direction as the old floor a layer of 6mm exterior grade plywood can be firmly fixed down and the new floor secret nailed with a nail long enough to penetrate the plywood and into the old floor. The plywood serves to stop the expansion and contraction of the softwood floor from affecting the new floor. The plywood can be laid as sheets or as strips at 300mm centres.

Under no circumstances is it recommended to fit a solid hardwood floor to a floating chipboard floor, as it is not rigid enough.

Underfloor Heating

When laying a floor where Underfloor heating has been installed it is important to follow these guidelines:

1. We recommend an Engineered Board rather than a solid floor
2. The heating has been on at least 3 weeks prior before laying the floor
3. Make sure there is not water leaking and the concrete is dry. This means no more than 3% moisture, full depth of screed
4. The concrete meets all the requirements for Underfloor heating
5. The surface temperature of the ground cannot exceed +27oC
6. We advise that the heating be switched off 48 hours prior to the laying of the floor

Engineered Floors

Engineered boards are ideal for Underfloor heating. Always use an underlay with a damp proof membrane when floating the boards. In large or odd shaped rooms, engineered boards should be glued and not floated.

Pre-Finished Floor (Finished)

Our automated process sprays lacquer on to ALL edges of the board totally sealing it to keep all moisture out.

We also offer a selection of different lacquers and finishes.

Finally a catalytic infra red drying system then dries any chosen finish and expels any odour quickly and efficiently. With some suppliers this process is carried out on installation, we prefer any odour to be in our factory – not your home.

Finishing a Millennium Hardwoods floor

Before applying any finish to your floor, the surface should be flat, smooth and clean. On new wood floors this should be carried out using first medium grit sandpaper (60-80 grit) followed by fine grit (100-120 grit) to ensure a smooth surface. Alternatively Millennium Hardwoods can supply boards pre-sanded to a 100/120 grit finish to save the work of sanding.

When complete, all dust should be removed (including ledges and skirting) prior to applying finishes. A wide range of finishes are available. Those we recommend are:-

Granglaze Satin – An oil based seal which gives a deep colour to wood similar to an oil finish. It is especially good on oak floors.

Application – All these finishes can be applied using a 12” applicator & Pad or a good quality brush. Rollers are not recommended. After thorough shaking and pouring into a suitable tray, the product should be evenly applied along the grain of the wood. When dry, the surface should be lightly sanded using fine sandpaper (160 – 180 grit) to remove raised grain.

After removing dust further coats are applied as directed. Three or four coats are usually required although heavy traffic areas may require additional costs.

When the final coat is dry the floor should be left for a minimum of 24 hours in domestic and 48 hours in commercial premises prior to light use.

The floor will remain susceptible to scratching until the full curing time is achieved (approx 7 days). The floor should not be cleaned or covered with rugs for this period.