Every timber surface needs to be properly prepared before you put a paint, stain or other coating on it.

Timber flooring is no exception. The better your preparations are, the better the finished job will be.

As is always the case with any new job, it's imperative that you carefully inspect the substrate to make sure there are no underlying issues that might cause problems later.

Most of the serious problems occurring in timber floors are related to moisture content.

You'll find more information on these issues in the unit: Inspecting and testing subfloors.

If you do find something that looks like it might cause trouble later, don't ignore it.

Remember, as a professional installer, it's your responsibility to decide whether the job is ready for you to proceed.

You'll be doing everyone a favour in the long run, including the owner, the original floor layer and yourself, if you raise any potential problems before you start, so they can either be fixed by the previous contractor or inspected by a specialist.

Below are the main preparations that either you or the floor sander should have completed before the floor can be coated.

Filling nail holes and voids

Some contractors like to fill the nail holes before they sand the floor, so that the filler is sanded flush as part of the overall process.

But others prefer to wait until after the first coat of finish is applied, particularly when using oil-based fillers.

This avoids the problem of the filler bleeding into surrounding wood fibres, or drying out too quickly as the timber sucks moisture out of the filler.

Either way, it's important to make sure that the filler is compatible with the coating system that will be applied.

Check that the filler completely fills the hole, so it doesn't later crack or come loose.

Sanding the floor

The sanding process is carried out with a range of machines, such as:

• drum sander, for the level or basic sand, which is designed to remove high points and ridges
  
  
• disc sander or 'edger', for working around skirting boards and into corners
  
  
• rotary or orbital sander, for the finish sand, which smooths off any coarse sanding marks and smooths the floor, ready for coating.

The number of passes required, and the grades of sandpaper used to complete each stage, will depend on the condition of the floor and the hardness of the timber species.

Between each sanding pass, the floor needs to be vacuumed thoroughly to remove all dust and dirt.

Special attention must be paid to cracks or other dust traps that might hold particles.

Sanding cork floors

Cork is much softer than timber and the tiles are much thinner, so it is normal practice to sand the floor with a plasterboard sander, also called a 'drywall' sander.

You can either use a power sander, which has a rotary action, or a hand sander on the end of a pole.