SANDING AND FINISHING

Equipment

You’ll need abrasive paper ranging from 80- to 320-grit and a few lengths of sanding block. Vacuum-purged sanding blocks with Velcro adhesives are inexpensive and effective. They reduce dust and last longer, as the abrasives don’t clog.

Apply guide coat

When you start to sand the surface, the filler will take on an even colour and you won’t be able to see what’s been sanded. Use a guide coat so you can see the low points. A dry guide coat system (pictured) is a handier alternative to aerosol types.

Sand first fill

Use 80-grit abrasive paper on a sanding block of an appropriate size. Keep it constantly moving across the whole surface and change direction frequently to gain the correct profile. Turn the abrasive through 180° to give it a second lease of life.

Check profile

The matt surface hides imperfections. Happily, hands are incredibly sensitive to such things. Look away from the panel and use the flat of your hand to detect high and low areas. Mark areas that require further dressing or filling lightly with a pencil.

Repeat the process

Apply a skim of fine filler over a larger area. Once it’s cured, apply a guide coat, sand it with 80-grit abrasive paper and recheck the profile. Repeat until a perfect profile has been achieved. Sand the final skim with finer 180-grit paper.

Flatting large areas

Large panels are tricky, as they can feel smooth while undulating over their length. Use a very long sanding block. Move it at a 45° angle rather than in a straight line and regularly swap it round to sand in a criss-cross pattern.

Filling swage lines

It’s hard to see the profile when filler has been applied, as it’s all the same colour. Apply a guide coat and sand one face of the swage. Reapply the guide coat and sand the other face. The contrast between the guide coat and filler will highlight imperfections.

Apply glaze

A glaze is a very fine filler used to fill tiny imperfections and level minor undulations. Apply it in a very fine skim. Apply a guide coat and flat back with 180-grit then 320-grit paper. Note the size of the filled area here in comparison to the original ding.

Apply filler primer

Filler (or ‘high build’) primer is the final stage. Aerosol types are most convenient for home use. Make sure it’s compatible with the filler and the existing paint. Build up coats as per the instructions, apply a guide coat and flat with 320-grit paper.