Laying wood flooring on an existing subfloor can sometimes bring about challenges. And tackling defects is key to ensuring a successful result. Here’s our advice on fixing subfloor issues to prepare for a sound and stable floor fit.
In older properties, subfloors may have deteriorated with age and may no longer provide a stable base for a new wood floor. Brand new screeds may need attention too.
Ensure any infestation or rot in timber subfloors is dealt with, and any loose or distorted joists and boards firmly fixed or re-levelled. Uneven boards can be overlaid with good quality plywood to provide a smooth, stable base.
It’s also important to consider the effects of covering up a traditional timber floor – check that airbricks are clear to allow airflow.
Old and New Screeds
Old floor screeds can often become soft and friable, and sometimes even structural concrete may need repair or replacement. Even a new floor screed needs to be checked for soundness, as a weak cement ratio or a badly mixed batch can sometimes result in a loose surface.
Repair weak patches by cutting back to sound material. Areas shallower than 50mm can be primed with Woodpecker Level-X Primer and filled with Level-X compound. Deeper repairs can be corrected using a sand and cement mix.
If adhesive or contamination is present, remove this by scraping or grinding, especially if a new wood floor is to be bonded down. Once a sound base has been achieved, seal the surface with a Woodpecker Level-X primer and re-finish with Level-X Compound for a smooth, reinforced surface.
Existing finishes such as plastic or ceramic tiles and parquet blocks should always be treated with caution as they may be disguising another issue. It’s also usually not possible to be sure how soundly bonded they are to the structural substrate.
As a general rule, it’s wise to remove any existing finishes and prepare the subfloor from a sound base. One point to look out for is that some older finishes may have been installed as a form of damp proofing, so once removed a new membrane may need to be installed.
There are a variety of other historical subfloor materials, and these can vary regionally. Some, such as asphalt, are usually stable and can often be overlaid with Level-X fibre-reinforced levelling compound before fitting the floor. Yet, other composite screeds can be very unstable and need to be removed. If in doubt, further research is always advisable to avoid a costly failure – our technical team are happy to help with any queries. We’re available on 02920 888 223 or email@example.com
Ensuring the subfloor is flat is vital for a good result. Wood floors can be intolerant to unevenness causing symptoms such as bouncing, squeaking, joint failure or adhesive de-bonding.
We recommend that bumps and dips shouldn’t exceed 3mm over any 2 metre area. Where undulation is greater, some levelling will be required.
Old joists can be shimmed to achieve a level structure on which to lay a new finish, and old boarding or plywood can be overlaid with a fibre-reinforced levelling compound such as Level-X.
Screeded floors can also be corrected with Level-X.
Many older properties (and even some brand-new ones), can suffer from moist subfloors. As this often can’t be fixed at the source, action should be taken to focus on protecting the new wood floor.
Use a DPM
A liquid DPM such as Woodpecker WP60 will hold back a fairly high level of residual moisture in a new floor screed, allowing it to dissipate slowly over time. Or, a polythene DPM with carefully taped joints will provide a simple and cost-effective barrier. Where moisture levels are higher or likely to continue (as is often the case in old properties), our Damp Proof Barrier offers a combined waterproof layer and underlay.
Where a new wood floor is being nailed down to an old timber structure or new timber joints that haven’t been dried, a separating membrane such as Moistop should be used to prevent moisture transfer.
Be aware too of damp subfloors where moisture levels may vary according to the groundwater levels as a period of heavy rain could create a more extensive problem than anticipated.
In some rare cases, the only safe course may be to remove and replace the existing subfloor completely and install a new structural damp proof membrane.
If you’d like any further advice about subfloor preparation, please get in touch with our Technical team on 02920 888 223 or firstname.lastname@example.org