Site Preparation Guide for Broadleaf Wood Flooring

Careful site preparation is key to avoiding problems with wooden floors after installation. Please check the following before flooring is delivered:

Environment

Flooring should only be installed into normal living conditions. As part of your subfloor preparation regime, ensure that the room is sealed, dry, free from damp, heated and within the following scope: 

* Temperature – 15-24°C 
* Relative Humidity – 40-65%

Damp

A wood floor should not be installed anywhere that suffers from damp. We advise the following site preparation checks to rule out obvious causes but please bear in mind that damp is seasonal and may not be evident at the time of inspection. An expert should be consulted if you have any concerns and all issues resolved before the floor is delivered. 

Make sure that solid ground floor subfloors have a damp proof membrane. If there is not, do not proceed with installation until this is rectified. 

Check that air bricks below suspended floors have not been removed or blocked up and that air circulation is sufficient to prevent moisture build up and that existing joists show no signs of moisture damage. 

Make sure that drains next to the house are free of leaves and debris so that they do not block and cause water to build up against walls or under a suspended floor. 

Check that walls do not show signs of water ingress or damp. 

Check the relative humidity of the room. Readings outside the normal range for a heated environment could indicate the presence of damp. 

Note: If a subfloor is sealed with a paint-on damp proofing product you should not breach this and should check that any adhesive you plan to use is compatible with it.

Plaster

All plastering in and near the room where a floor is to be fitted must be complete and fully dry before the flooring is delivered. 

This will require at least 2 weeks from change of colour, which is generally about 2 weeks from application of plaster to plasterboard, and 4 weeks from plaster to render. Damp weather and other environmental conditions can extend this.

Pipes

Underfloor pipes (excluding underfloor heating which is dealt with separately) should be properly insulated to prevent hotspots and localised shrinkage. 

Although it is not always practical to deal with this retrospectively, check the floor with the heating on to identify any unusually warm areas. Resolve these by lagging pipes where these are accessible. Be aware that otherwise some localised shrinkage of boards may occur after fitting. This will normally only be an aesthetic issue and is unlikely to affect the structural integrity of the floor.

Subfloors

The condition of the subfloor is integral to the stability and performance of the finished floor, and as such, this is one of the most crucial aspects of site preparation. As a general rule, all subfloors should be dry, level and free from dust. 

Concrete subfloors must contain a damp proof membrane and have a moisture content of no more than 4% (by weight) as measured with a Tramex concrete encounter meter. These meters should not be confused with a standard damp meter, they are specialist meters – essential for subfloor preparation – and can be borrowed from Broadleaf showrooms. 

Generally, existing screeds should meet this criteria unless they are damp. New concrete up to 50mm thick will normally take approximately 1 month per inch (1 day per mm) to reach it. Thicker screeds can take longer. 

A good preliminary test is to fix a small area of plastic sheet to the surface of the concrete with airtight tape. After a couple of days, check the underside of the sheet. If there is no condensation present, then it is likely that the 4% level has been reached, but be sure to check with a meter before proceeding to installation. 

If you are going to glue-fix flooring directly to a screed or float Strata over it, it must be level to within 3mm across 2 metres for the adhesive to be fully effective. Check this at the site preparation stage, and resolve any more significant imperfections with self levelling compound or ply prior to delivery of the timber. 

Before glue-fixing, we also recommend the application of a primer to aid bonding and offer an additional moisture barrier. This must be compatible with the recommended adhesive. With Broadleaf Ultra Adhesive use Broadleaf Ultra Dry Moisture Barrier & Primer.

To nail-fix flooring above concrete, you will first need to install softwood battens. These must be dry (request them as such from builders’ merchants) and a minimum of 20mm x 50mm. They must be screw-fixed at a maximum of 400mm centres at 90° to the intended direction of the floor. Insulation can be added between the battens if desired. Battens should be packed as necessary to ensure that the surface is level. 

Timber subfloors should be structural flooring-grade plywood or chipboard (T&G) or existing floorboards. Plank flooring can be nail-fixed directly to chipboard/plywood in whichever direction is preferred. For added stability and sound insulation we recommend using glue as a supplement to the nails, applied in strips every 300mm. Strata boards can be floated over this style of timber subfloor and parquet can be glued. 

In the case of existing floorboards, these must be dry, reasonably level and firmly fixed. If they are not reasonably level we recommend that you remove them at the site preparation stage and, product permitting, fix the new floor directly to joists. (see below). 

If they are reasonably level and are on the ground floor, check that air bricks are present and clear and that there is no moisture build up beneath the existing boards. Bear in mind that this must be the case all year round. Sound, rot-free joists are a good indicator that this is the case. Cupping in the surface of the existing boards could highlight a problem. If there are moisture issues, do not proceed with the installation until these have been resolved. 

All being well, screw down any loose boards – check beneath them for services first – punch back any face nails to just below the surface of the boards and sand out any significant high points. Once subfloor preparation is complete, plank floors can then be nail fixed over the existing floor at 90°, eliminating the issue of any residual unevenness in the surface of the old boards. 

If you want to fix the new floor in the same direction as the old floor, you will need to overlay this with flooring grade plywood or chipboard at least 18mm thick, and then fix to this as noted above. Again, in this instance it may be easier simply to remove the existing boards during site preparation and fix the new floor directly to the joists. 

Joists need to be structurally sound, dry, rot-free, relatively level and at no more than 400mm centres. 

For ground floor installations the space beneath them must be free of moisture and you must be confident that this is the case all year round. During site preparation, always check that air bricks are present and have not been blocked up, there is no moisture in the space beneath the joists, and the joists themselves are sound and rot free. If you are in any doubt, consult a damp expert before proceeding with the installation. 

Lay the floor at 90°to the joists, packing where necessary to ensure that the floor is level. 

Tiled or stone floors are not recommended as subfloors. Ideally, these floor coverings should be removed and any wood floor fixed directly over the concrete subfloor beneath once this meets the required criteria. If this is not possible, or practical, then a suitable damp proof membrane must be installed over the tiles/stone followed by tongue and grooved plywood (18mm min). The flooring can then be fixed over this as recommended for the product. Remember that any nail fixing will need to remain within the thickness of the ply.

Heating

Once any new concrete has reached the required moisture level and plaster is fully dry, the heating must then be run to drive out any latent moisture before the flooring is delivered. Conventional heating should be run for a minimum of 2 weeks (even in summer). For underfloor heating recommendations see our Underfloor Heating page.

Acclimatisation

All Broadleaf flooring products must be acclimatised for 7-14 days before installation. They should not be delivered to acclimatise until all concrete and plaster are fully dry (see section 1) and the heating has been run for a minimum of 2 weeks after this (see above). 

Keep them in the room where they will be fitted, or one with similar environmental conditions, unwrapped and lattice stacked (criss cross) so that the air can circulate. In particularly dry or damp weather, or if using wide boards, err towards the upper end of the recommended acclimatisation period.

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