Understanding the Limitations of Self-Levelling Compound on Timber Floors
Applying self-levelling compound directly onto traditional timber floorboards is generally not advisable due to issues such as gaps, uneven steps, and the natural movement of the timber. These factors can compromise the adhesion and stability of the overlay, leading to potential problems in the finished floor.
Most professional domestic floor layers recommend over-boarding the existing floor with a minimum of 6mm thick plywood before applying any self-levelling compound. This additional layer creates a stable, smooth, and level surface suitable for further flooring finishes. It’s essential that the original floorboards are firmly fixed to the underlying joists before over-boarding, typically achieved by securely screwing the boards down with appropriate wood screws. For detailed guidance, refer to our article “How to Ply over Floorboards”.
Self-Levelling Compound on Chipboard Floors
Can you use self-levelling compound directly on chipboard? The answer is generally yes, provided the chipboard flooring sheets are properly installed. When tightly interlocked and adequately screwed down, they form a suitable sub-floor for self-levelling compounds. To ensure optimal results, seal any gaps around the perimeter of the room with silicone or expanding foam to prevent seepage and unwanted leakage of the compound.
Unlike traditional timber floorboards, chipboard sheets usually interlock tightly, reducing the risk of gaps and steps. This makes them more amenable to direct application of self-levelling compounds, assuming the surface is stable and well-fixed. However, significant gaps, steps, or cut-outs—especially around pipework—may still warrant over-boarding with plywood for a smoother, more reliable base.
Addressing Gaps Between Floorboards
Gaps between individual boards can allow the self-levelling compound to leak out during pouring, creating messy situations and potential structural issues if the compound escapes into ceilings or below. Over-boarding with large sheets of plywood helps substantially reduce the number of joints and gaps, providing a more sealed and consistent surface for levelling.
Managing Steps and Unevenness
Many timber floors exhibit small steps, often up to about 2mm, where individual boards meet. These unevennesses can cause issues, especially if some boards protrude through the finished surface of the self-levelling compound. Over-boarding with plywood helps to level out these minor discrepancies, resulting in a seamless, smooth floor surface with fewer visible joins.
Dealing with Floor Movement
Individual timber floorboards tend to shift slightly when walked upon, which can lead to cracks or delamination in the self-levelling layer. The solution is to over-boarding with plywood, which is securely screwed to all the underlying floorboards. This method ensures the entire surface moves uniformly, preventing cracks and providing a stable, unified base for subsequent flooring installations.
Screwing Down Floorboards for Stability
When fixing timber floorboards with wood screws, aim to position the screws adjacent to the original fixings. This practice ensures the screws penetrate into the underlying floor joists, enhancing stability and reducing the risk of screws hitting pipes or electrical conduits—particularly crucial in areas like bathrooms or kitchens.
Using Self-Levelling Compound on Chipboard Floors
If your chipboard flooring contains numerous gaps, steps, or cut-outs—especially around pipes—it may be more effective to over-boarding with plywood rather than attempting to apply self-levelling compound directly. For comprehensive guidance, consult our detailed article “How to Ply over Floorboards”, which covers the fundamentals of preparing and over-boarding floors to achieve a perfect, level surface.