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Solid Oak Floors Guide

Timber will continue to take in or let out moisture in harmony with the surrounding environment where it is located.  Unless otherwise informed, once delivered to the site the timber floor should be acclimatised (laid horizontally or criss-cross in the location it is to be finally laid) for a period of 10-14 days, longer periods would help further. Without such a period problems may occur.

Average room temperatures should be between the range 15 degrees and 25 degrees Centigrade and the average Relative Humidity should be between 35-65%. An environment where the room temperature is likely to exceed 25/27 degrees Centigrade and the Relative Humidity % falls below 35% for any length of time should be looked upon as ‘extreme’ and unsuitable for any form of wood flooring, especially solid oak floors. Moisture is also a factor that effects potential movement. Limit fluctuations in moisture (Relative Humidity) and you limit the desire for timber to move.

Before installation and before the wood is delivered please ensure that:

a) A concrete floor should be sufficiently dry (75% Relative Humidity) and contain a damp proof membrane. Even though most modern floor slabs contain a DPM, in our opinion it is necessary to install a surface membrane before installation of the flooring, to ensure that the wood does not come into contact with any inherent damp that may be in the floor slab (‘belt and braces’). If a solid timber floor is laid on or near a concrete subfloor that is not dry moisture will eventually evaporate and in so doing it will be absorbed by the timber floor, which would then need to expand. As a guide, concrete slabs may take at least 1 month per 25mm thickness of slab i.e. for a slab 100mm thick. Thicker slabs will take longer than 1 month per 25mm thickness.

b) Plaster has been allowed to dry out (4+ weeks for solid plaster and 2-3 weeks for dry lining).

c) Wet trades such as tiling have been completed and the areas allowed to dry out (3+weeks).

d) Windows and external doors are fitted.

e) Radiators are fitted, tested. bled and functioning at a medium level of temperature.

f) All painting and wallpapering is completed and has been allowed to dry (1+week)

Installation Guidelines – solid wood flooring (Never float solid oak floors).

For boards of up to 160mm wide we would suggest fixing using the secret nailing method (if the timber is going over existing timber flooring, please check cables, water pipes etc. before using this method and we strongly recommend the use of a moisture barrier (such as Sisalkraft Paper 728) to isolate the new wood from the old).

Using a secret nailer and 50mm long serrated T nails fix the boards at a 45 degree angle through the base of the tongue at 300mm centres or less. This method can be used over existing floors, battens and plywood. If the flooring is to be fitted over joists, then the floor should be laid at 45 or 90 degrees to the joists and nailed where possible, but at not more than 300mm centres.

Laying solid wood “floating” over an underlay or glueing the tongues and grooves at the sides is not a recommended method of fixing.

Additional Information

Any wood flooring should not be fitted over joists over a poorly ventilated cavity. The timber will absorb moisture and expand. In these circumstances it is best to board over the joists with moisture proof plywood or with a waterproof membrane, such as Sisalkraft paper 728, which can be laid with ply and fit the floor using the secret nailing method.

If the floor is concrete then battens should be used fixed either by adhesive or screwing into the concrete. You can, if you wish insulate between the battens. Fix the flooring using the method described above, and with a moisture barrier such as heavy duty Sisalkraft paper 728 laid between the new boards and battens/joists to isolate the boards from any possibility of moisture. (Belt & Braces approach).

For solid wood boards wider than 160mm just using the secret nailing method is not enough and these need to be face fixed as well, either by plugging and screwing, screwing and filling or by using decorative nails.

The battens must be kiln dried with a maximum moisture content of 12-14% and placed at 300 mm centres at right angles to the direction of the timber floor.

Expansion Gaps

10/15mm gaps need to be left around the perimeter of the floor. Depending on the size of the room intermediate gaps 1-1.5mm may also need to be left across the floor, (so-called penny gaps – say, every 4/5 boards) particularly when wood is laid in the winter months and has been acclimatised with central heating running, causing the floor to contract. Without such expansion gaps when the floor expands it will either push upwards or push outwards i.e. either creating a dome effect in the centre of the floor or even pushing outwards a row of bricks from the base of a wall.

It is normal to expect during certain times of the year, a difference in the width of the joint between boards, caused through increase or decrease in the Relative Humidity. e.g. during the warmer weather there will be an increase in the Relative Humidity level: the boards absorb this additional moisture and expand across the face of the board. Consequently the joints become tight and a dehumidifier may be advisable.

In the winter period heating raises the temperature, which results in a drying-out of the environment which creates a shrinkage of individual boards and the joints between the boards increase in width.

During the winter months using a humidifier in the building would inject moisture back into the environment creating a long term stability of humidity that ensures the flooring remains stable.

Maintenance for oil treated floors – A dust attracting mop, very soft broom or vacuum cleaner will be sufficient for daily care. When necessary the floor may also be cleaned with a damp cloth previously impregnated with water containing a small amount of a professional wash and care wood floor cleaner, such as Osmo Wash & Care, then wiped dry to avoid moisture penetration into the joints of the flooring. Heavy stains should be removed with a cleaner such as Osmo Liquid Wax Cleaner. We can provide details of suggested maintenance products. Always have a dust-attracting mat at entrances to prevent sharp stones or dirt scratching the floor and use felt pads on the feet of furniture to protect the floor from excessive scratching.

It is recommended that wood flooring is installed by a professional flooring contractor

Stone and Wood Floors has used reasonable care in the preparation of this document but does not accept responsibility or liability suffered or incurred as a result of its use or reliance on it December 2016.


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