Preparation of new and existing subfloors

Covid 19 Update Read More

We are open for business as usual (although there here is nothing usual about this situation) with our transport company (Brooks Transport) who are designated by the government as critical to the covid response. We are still delivering direct to door or site, (however collections or visits to the warehouse are not possible.) Our IT systems allow us to work from home so our staff are protected. Please Call or Email Us for samples or orders. Our factories are back to full capacity and the supply chain is operating effectively which can be seen here. As a trade supplier we have a minimum requirement of 50m2 for any samples and supplies. Please call 01666 504015 if you require less. For Government advice please click here. Even with these steps we have made, we must pull together, support one another, and get through this as a group, a family, and feel proud to say to our wider community we are critical to the Covid-19 response, and we will support it for as long as we are able. Stay safe, stay well, look after yourself, and each other.

The Building Centre will be open fully with the café back and exhibitions in place from Monday 12th April 2021. In the meantime, you can book visits in advance by contacting The Building Centre directly on 020 7692 4000. Please note that we do not have any representatives based at this showroom, but you can call us during your visit to talk through the options on display on 01666 504 015.

The Tetbury showroom is strictly by appointment only, maximum of two people with social distancing and face coverings required. Please call 01666 504 015 to book an appointment.

Preparation of New & Existing Subfloors

Subfloors and the issues surrounding them

A subfloor is what is underneath your present floor covering. Subfloors can become a nightmare if you do not follow the correct procedures because whatever goes on top of the subfloor will be affected by it.

Damp, damaged membranes etc can allow moisture to rise upwards, moisture will always go to the driest part. Our fitters will check the floor for moisture and the surrounding area for humidity to ensure that there will be no problems once the floor is laid. The moisture content of the floor screed should be checked along with the relative humidity.

If the following procedures are followed then you will be providing the right environment for a beautiful natural floor that should last a lifetime and you will not get “cupping” or warping problems which only occur where there is excessive moisture. Cupping is where the edges of the boards curl up.

Types of Subfloor

There are 5 basic types of sub floors upon which we fix hard wood floors.

  • Concrete screeds, power floated floors
  • Joists
  • Ground floor joists with open air below which are found in old houses that have air bricks and probably earth underneath
  • Old floor boards
  • Chipboard or plywood structure
  • Underfloor Heating Screed

Concrete: Concrete screeded floors can vary in condition and levels.  If it is flat and smooth with a moisture content of 2% or less then we can glue the boards directly to the floor using our advance SW-890 flooring adhesive, which is generally the best method of fitting rather than floating the wood floor with underlay.

If your subfloor is not flat and smooth you can use self leveling compounds but be aware that they can lift if you do not apply the compound correctly.

If you have your own builder or fitter please make sure they are experienced in fitting wood floors and understand the consequences of not following the correct procedures for concrete screeds.

To be extra cautious you should always put a Damp Proof Membrane (DPM) like the Bona R580 on any concrete screed.  Some concrete takes 10 years to dry out completely and if the membrane underneath cracks for any reason such as subsidence (which can happen in long dry spells) then moisture can work through the screed and affect the floor. 

Joists: If you are fixing floor boards directly to joist you can either use secret nails or screws.  These are applied using a purpose-made nail gun or screw fixer which is set at a predetermined angle so that the groove of the next board can be fitted up without the screw or nail showing.  

The joists must be in good condition and free of any wood worm, damp decay, dry rot or any other fungal type disease that can affect their integrity.  

Older homes in the Victorian and Edwardian era had joists over open ground with air bricks if the circulation is blocked then it can lead to serious damp problems. If you have enough height then a plywood base using at least 18mm marine plywood.  The ply can be screwed to the joists and the floor boards glued directly to the plywood.  This will cut out drafts and prevent the damp air affecting the boards.  If you do not have the height due to the existing fixtures in the house then you must always use an engineered board and ensure that all the ventilation openings and air bricks are clear

Old Floor Boards: Generally old floor boards will be pine or cheap softwood.  If these boards are sound, free of dry rot and fungus, then a new hardwood floor can either be secret nailed, screwed or glued directly on to these boards.

If the boards are loose then it would be best to screw them firmly into the joist. If necessary an acoustic can be placed between the two layers of wood when nailing or screwing down, this will reduce noise levels including creaking and helps to reduce the transmission of cold air from below.

If you are unsure then our fitters would be happy to make a site visit to ascertain the best way of fixing your floor

Chipboard or Plywood Floors: Chipboard and ply wood sub bases are the ideal surface to fit a hardwood floor. You will be able to choose any of our wooden floors and on plywood they can be nailed, screwed or glued, but on chipboard due to it being particles of wood and glue nails and screws would not hold properly over time so it is always best to glue the floor boards down.

Underfloor Heating: This is a specialist area and should be treated with care. Whichever system you have, the manufacturer’s instructions should always be followed. If it is a screeded system then always glue the boards direct to the screed this ensure not heat loss You can find out more in our underfloor heating section.