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QI’ve just tidied some rust scabs on my Austin A40. I bought some ‘matching’ paint, but the match was terrible. I’ll have to get some more – but what if it’s just as bad? What paint do you recommend? I had a choice of four types and ended up picking at random. Sandy Grisham, Chipping Sodbury
APaint matching is a very tricky business. A number of pigments are blended to give the intended colour. The balance is so fine that it’s impossible to guarantee that exactly the same shade will be produced every time, even if the paint is made to the same formula. Even in car factories the shade of a given colour varies from batch to batch. Thus, the single formula that your paint factor uses to mix the paint will not necessarily be accurate.
It’s a lottery. For some colours the difference is almost indistinguishable; for others, the mismatch is visible from space. To add to the confusion, a paint that matches in daylight can look totally wrong under artificial lighting. Paint changes colour as it gets older, too. You can polish away the dull oxide layer with T-cut, but sometimes age and ultra-violet light cause chemical changes to the pigments. Also, your car may already have been repainted in a slightly wrong shade.
It’s worth taking the fuel filler flap, or similar, with you when buying paint. It’ll help if there’s confusion about the colour – and a good paint matcher should be able to tint the paint to correct any mismatch. Some firms can scan the colour with a computer and produce a custom tint.
What paint type to choose is more straightforward. Aerosols are handy for large areas, but impractical for stonechips. You can generally obtain ‘normal’ paint in 250ml or 500ml tins. This is thick enough to touch-in a chip, but can be thinned-down and used in a spraygun for larger areas. It’s an economical way to buy it, too.
Cellulose paint has been the default choice of the amateur car repairer for many years. Fast-drying, it can be lightly rubbed-down and recoated quite quickly if the finish is poor, so it’s almost foolproof. It’s perfect for touch-ups and spraying, but it’s very hard to brush it over large areas due to its fast drying time.
Synthetic enamel or singlepack polyurethane paint is slowdrying and can be used for brushing or spraying. The slow drying time can be a nuisance, as it can sag and run badly on vertical surfaces. It’s better than cellulose for brushing over
a larger repair area, though, as the brush marks ‘flow’ out. Leave it well alone for at least a couple of hours afterwards. Thin it with white spirit.
Single-pack acrylic paint requires its own special thinner, though this isn’t expensive. It combines the fast-drying of cellulose with the free-flowing ability of synthetic paint – so brush and spray marks have time to flow out and disappear, but runs and sags are less likely to develop. It also tends to have good opacity when quite thin, meaning patches of primer won’t show through.
Water-based paint needs a lacquer on top of it, so it’s not appropriate unless you car has a lacquered finish to start with. Two-pack acrylic paint requires mixing with a separate hardener. It contains (to cut a long story short) a respiratory irritant. You’ll need an air-fed mask, an all-over suit and gloves if you intend to spray it.