How to Ply over Floorboards
It is often best practice to over-ply old floorboards before you apply a new floor covering or self-levelling compound. If your floorboards are gappy and uneven the plywood will help to create a smooth unified surface, that is ready for your finished floor covering or self-levelling compound to be applied.
How to Over-ply floorboards
The first step is to ensure that the floorboards are screwed down to the joists. If the floorboards are loose to start with, then over-plying them will not work as effectively. The floorboards underneath may still be able to move and creak.
Now the floorboards are fixed securely, you can start to Ply over the floor. It can be best to try and run your plywood sheets in an opposing direction to timber floorboards. But this is not essential as the main aim here is to fit the plywood with as fewer joints in it as possible.
I prefer to use 6mm Plywood as it does not raise the floor level greatly, but it is still thick enough to bridge most gaps and steps in a timber tongue and groove floor.
Once you have cut the Plywood to size you will need to fix it down to the floorboards with small screws. The screws need to be just long enough to go through the Plywood without sticking out at the back of the floorboards. If you are using 6mm plywood and you have 20mm thick floorboards then 4.0 x 25mm screws will be ideal.
It is always best to fix each piece of Plywood down with one screw in each corner to start with. Once you have got all the Plywood sheets into position, you can then start to screw them all down.
The quickest way to ensure that you have the correct amount of fixings distributed equally across the floor is to draw a 150mm x 150mm grid. Then pilot a 4mm hole where the gridlines intersect. Then place all your screws in the pilot holes and work your way around screwing them all in.
The pilot hole should go just deep enough to go through the 6mm Plywood but not into the Floorboards behind. The pilot hole should be the same diameter or slightly larger than the threads of the screws you are using.
If you are using 4.0 x 25mm screws then a 4mm-5mm drill bit will be perfect.
Drilling through the plywood means that the screw will go into the floorboards behind, pulling the two surfaces together, and effectively clamping the plywood to the floorboards. If you fail to pilot the plywood it will not work as effectively.
A countersink bit can also be useful to help the screws finish flush or slightly below the surface. If the screws are proud of the plywood then they can show through the self-levelling compound or finished floor covering.
If I am doing a large floor I tend to set myself up with three drills. One with a Pozzi Driver bit, one with a drill bit, and one with a Countersink bit. If you drill all your pilot holes, then countersink them all, then fire in all your screws – you will be fine with just one drill. The key is to get organised before you start, this will save you tons of time on the job!
