Contract Flooring Journal (CFJ) the latest news for flooring contractors

Home> F Ball <The stages of subfloor preparation

The stages of subfloor preparation

Neil Sanders talks through the necessary preparation procedures to achieve a flawless flooring finish.

The application of a smoothing underlayment is recommended to create a smooth base for floorcoverings as part of any flooring installation. Equally important for ensuring that installations look as good as possible for years to come is properly preparing the subfloor beforehand.

Here I’ll talk through the necessary preparation procedures to achieve a flawless flooring finish.
Although undertaking proper subfloor preparation should be routine practice, neglecting to do so often results in floor failure, the leading cause of which is still unmanaged excess subfloor moisture. The following steps are essential for creating a suitable base for the installation of floorcoverings.

Initial preparations
The first stage in any flooring installation should be ensuring the subfloor is suitably sound and smooth. If a newly installed screed is present, contractors will need to ensure that any laitance, the crust of cement and fine aggregates that forms on the surface of the screed as it dries, is ground off. If not removed, laitance can cause subsequently applied smoothing underlayments to de-bond from the substrate, potentially causing floor failure. The normal method of removing laitance is using a rotary sanding or abrading machine.

If the project is part of a refurbishment, the condition of the subfloor will need to be assessed once old floorcoverings have been removed. It may be discovered the subfloor is cracked or damaged, in which case extra preparation will be required. In most cases, cracks as deep as 50mm can be filled with a floor repair compound.

Subfloors may also be contaminated with oil, grease or other chemicals, necessitating mechanical preparation by grinding, abrading or grit blasting before applying other floor preparation products. Contractors should refer to British Standard (BS) 8204 for guidance on testing if it’s possible to mechanically prepare concrete bases for the receipt of in-situ floorings where contamination is present. Old adhesive residues will need to be removed by mechanical means unless a smoothing underlayment that is suitable for use over old adhesive residues will be used. Any other contaminants that may prevent adhesion, such as wet trade waste or debris, should also be cleaned off.

Dealing with damp
Contractors must take care to ensure the substrate is dry enough to proceed with a flooring installation. Whether the result of rising damp or residual construction moisture, unmanaged subfloor moisture can attack adhesives and floorcoverings, possibly causing complete floor failure.

For this reason, F Ball recommends a moisture test is conducted to determine subfloor relative humidity (RH) levels as part of any flooring installation.

A calibrated digital hygrometer will give accurate readings of subfloor moisture levels as a measure of relative humidity (RH). Where relative humidity of the subfloor is 75% or above (65% for wood flooring installations), a moisture management solution must be installed to prevent subfloor moisture rising up to the level of the floorcovering and causing floor failure.

F Ball recommends the use of a two-part epoxy waterproof surface membrane system, such as Stopgap F77, which cures rapidly (about three hours at an ambient temperature of 20deg C) to create a barrier against moisture where RH values are up to 98%.

Prime importance
Once satisfied the subfloor is sound, smooth and dry, or an appropriate moisture management solution is in place, the application of an appropriate floor smoothing underlayment will create a uniform, smooth surface over which to install the final floorcovering.

In most cases it will be essential to prime a surface beforehand. This promotes the optimum performance characteristics of the smoothing underlayment and, when used over absorbent subfloors, such as concrete, prevents moisture being drawn from the smoothing underlayment too rapidly.

When working over raised access panels, cement-based primers, such as F Ball’s Stopgap Fill and Prime, are available that fill the gaps at the joints between the panels while simultaneously priming the subfloor. The product can also be applied to mechanically fixed and glued P5 flooring grade chipboard prior to the application of a recommended smoothing underlayment, removing the need to overboard the subfloor with plywood.

Smoothing underlayment selection
Finally, contractors should then take time to ensure they select the optimum smoothing underlayment for a particular situation.

For example, smoothing underlayments with high compressive strength should be used where floors will be subject to heavy loads or high foot traffic. For contractors working to tight timescales, fast-drying smoothing underlayments are available that will be walk-on hard from just 30 minutes and ready to receive floorcoverings in as little as 45 minutes after application.

Only by following these steps will you meet the highest standards for flooring installations and have the peace of mind that comes with being assured of avoiding costly floor failures – F Ball guarantees its products will perform for the entire lifetime of a flooring installation, providing the advised subfloor preparation and installation procedures are followed.
Neil Sanders, technical director at F Ball and Co

Please click to view more articles about

Stay Connected




Popular articles