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Stone & Wood Floors

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Underfloor Heating Guide

Fitting engineered timber floors over under floor heating:

This guide is a recommendation only and in no way should it be construed as a guarantee. If using timber flooring, care should be taken with the temperature that the underfloor heating is running i.e. the surface of the sub floor should be running at no higher than 27ºC, floor stats should be sited at floor level and checked on a regular basis using an infrared surface thermometer. Rugs or other floor coverings should be used to a minimum because the timber flooring can become too dry and may well result in some splitting or even delamination. Large items of furniture can also cause a similar effect and care should be taken when arranging. Electric Mat U/F/H systems need very careful management

Preparation for under-floor heating installation:

The following instructions for the starting of the under floor heating should be followed closely in both summer and winter.

All under floor heating systems, whether a wet system or an electric mat system, should have floor stats.

The heating layer of the cement should be allowed to dry out for approximately 21 days prior to starting. Beginning at 15 degrees for 24 hours and increase by 5 degrees daily until maximum temperature of 27 degrees on the surface of the screed has been achieved.

Run at this temperature for a few days or at least for 24 hours for each centimetre of the heating layer, then reducing by 5 degrees every 24 hours down to 15 degrees and then turn off at which time the floor can be acclimatised and then laid.

Preparation for a floating floor installation for both solid sub-floors and over under-floor heating:

Without gluing lay the first two rows of boards exactly together and parallel to the walls using spacing wedges (10 to 15mm).

The off cut from the first row should be used to start the beginning of the second row (for stability the off cut should not be less than 60centimetres). When you are happy with the fit remove the second row, apply a bead of the PVA glue to the top of the tongue on the long side and the head joints and re-position. You can now continue laying and gluing the floor using a damp cloth to remove excess glue. Allow the adhesive to dry for at least 12 hours before you remove the spacing wedges and put any weight on the floor.

The boards can be floated over under floor heating using the method as described above and a 3mm Universal underlay. The under floor heating system needs to be up and running for at least 3 weeks before fitting which allows:

  • All snagging with the heating system can be completed
  • That the sub floor is dry

Preparation for Gluing Method over Under-floor Heating:

Start in the corner where the two longest straight walls come together and preferably lay your floor in the direction of the incoming light. Use an adhesive, such as MS Flex, which has been made specifically for this type of installation.

Without gluing lay the first two rows of boards exactly together and parallel to the walls using spacing wedges (10 to 15mm). The off cut from the first row should be used to start the beginning of the second row (for stability the off cut should not be less than 50cms).

When you are happy remove the boards and wedges and apply the recommended adhesive with a trowel (toothed at 3mm) over that area and re-fit the wedges and boards.

Continue to apply glue to the floor and fitting the boards but work in areas of 1m2 at a time removing any excess glue with a damp cloth. To ensure overall adhesion cover the floors with weights, this can be removed after 12 hours along with the wedges.

Three days after installation is complete the temperature of the under-floor heating should be increased by 5 degrees daily to a maximum floor temperature of 27 degrees. When the full temperature is reached it can then be reduced by 10 degrees.

The under-floor heating can now be used normally to a maximum floor temperature of 27 degrees; however, we recommend that the room temperature be between 18-22 degrees with a relative humidity of 50-60% the ideal for timber floors.

If the underfloor heating system is the type that is set in insulation between joists or batons then a structural board i.e. 20mm/22mm can be secret nailed into the batons

If these guidelines are not followed the wood may swell, contract split or delaminate.


Protect your floor from Dirt, Stones and Water by installing a large dirt attracting mat at all entrances.
Felt pads under furniture legs reduce scratching.
Regular cleaning increases the durability of the finish. (Please see the Osmo Care & Maintenance Instructions).
Remove any sticky residue or soil by wiping with a damp cloth and all spillages should be mopped up immediately.
Ladies’ high heels will dent any wood flooring.

Key Points for Wood Floors over U/F/H

  • Solid Floors are not suitable
  • Do not fit wooden floors over damp sub-floors (over 2%rh)
  • Do not fit floors in damp conditions (plaster walls still damp, no windows, rising damp etc.)
  • Do not store timber in damp conditions for long periods of time-even in plastic wrapping
  • Do examine site conditions before fitting a timber floor-this should include sub-floor and air humidity check)
  • Do use an experienced and professional installer
  • Do maintain your floor

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