How to Over-Ply Old Floorboards
Applying an extra layer of plywood over existing floorboards is a highly recommended step before installing new flooring or self-levelling compounds. This process helps to stabilize irregular, gappy, or uneven floorboards, creating a flat, uniform surface that ensures your finished floor looks professional and performs well. Over-plying can also help prevent creaking and movement in the floor, extending its lifespan.
Step 1: Secure Existing Floorboards
The first crucial step is to make sure that all existing floorboards are firmly fixed to the underlying joists. Loose floorboards can cause instability, unevenness, and noise, which will compromise the effectiveness of over-plying. Use appropriate screws or nails to secure any loose boards, ensuring a solid foundation for the new layer.
Step 2: Planning Your Plywood Overlay
For optimal results, it is advisable to run your plywood sheets perpendicular to the direction of the original floorboards. While this is not strictly necessary, it can help improve stability and reduce joint alignment issues. When selecting plywood, a 6mm thickness strikes a good balance; it is thick enough to bridge gaps and unevenness without significantly raising floor height. If your floorboards are tongue and groove, this thickness is usually sufficient to create a smooth, level surface ready for subsequent finishing layers.
Step 3: Cutting and Fitting the Plywood
Measure carefully and cut the plywood sheets to fit the space, minimizing joints and overlaps. Proper sizing reduces the number of joints, which can be points of weakness. Once cut, position the sheets on the floor, ensuring they sit flush and are properly aligned.
Step 4: Securing the Plywood
Use small, appropriate-length screws to attach the plywood to the underlying floorboards. For instance, if you have 20mm thick floorboards, 4.0 x 25mm screws are ideal. These screws should penetrate through the plywood and into the floorboards without sticking out at the back. Begin by fixing each sheet with one screw in each corner, providing initial stability. Afterward, screw down the entire sheet systematically.
Step 5: Achieving Even Fixings with a Grid System
To ensure an even distribution of screws, draw a 150mm x 150mm grid across the plywood surface. At each intersection, drill a pilot hole using a 4mm bit—just deep enough to penetrate the plywood without going into the floorboards behind. Insert the screws into these pilot holes, tightening them securely. This method guarantees consistent fixing points, reducing the risk of movement or squeaks later.
Step 6: Pilot Holes and Screw Placement
The pilot holes should match or slightly exceed the diameter of your screw threads (e.g., a 4mm drill bit for 4.0mm screws). Drilling through the plywood allows the screw to draw the plywood tightly against the floorboards, effectively clamping the layers together. If you skip pilot drilling, screws may not seat properly, compromising stability. Additionally, a countersink bit can be used to sink the screw heads flush or slightly below the surface, preventing protrusions that could interfere with subsequent layers or finishes.
Step 7: Organizing Your Tools
For larger floors, consider preparing three drills: one fitted with a Pozzi driver bit for driving screws, another with a drill bit for creating pilot holes, and a third with a countersink bit to finish screw heads flush. Setting up your workspace with all necessary tools and performing the steps sequentially will save considerable time and effort, ensuring a smooth and efficient installation process.
Remember: Proper preparation, precise measurements, and organized execution are key to achieving a durable, level base that will support your new flooring for years to come.