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I’d like to coachpaint my Austin Ten. I vaguely recall a Practical Classics feature on how to do this some years ago. Can you refresh my memory? Bill Briggs, Petersfield
We showed a traditional method in the October 2013 issue. We used synthetic enamel paint thinned with white spirit and applied by brush. A coat of primer was followed by a number of applications of thick undercoat. This was rubbed down to a perfectly smooth surface and a couple of top-coats were applied. All rubbing down was done wet using relatively fine grades of wet-and-dry paper.
We recently chatted to Steve at Gilbert Michaelson (gilbertmichaelson.co.uk) on the matter. He offered an updated method that takes advantage of modern materials. You can still use a brush throughout if you want to avoid spraying. All rubbingdown is carried out dry to minimise the possibility of microblistering and the grades of abrasive are considerably coarser to increase adhesion. We’ll be mentioning specific readily-available products here, because experience has shown they’re the easiest and most reliable to work with. They’re all common enough. If you can’t buy them off-the-shelf or order them at your local motor paint factors, you’ll find them online.
Ideally, start by rubbing down to bare metal. It’s impossible to guarantee that old paint won’t interfere with the finish, either immediately or later on. Key the surface with P80 abrasive and apply a coat of MIPA Grundfiller. This is an epoxy filler-primer. It’s mixed with a hardener but it’s not a ‘two-pack’ as such, so you won’t need to don two-pack protective gear. When cured, rub to a smooth surface with P80. Apply U-pol Big Easy body filler, as necessary. This will bond directly to the abraded primer – don’t grind it back to bare metal.
Smooth the filler with P80. Apply two or three more coats of filler-primer as necessary. Rub down with P180 abrasive. Apply a wispy ‘guide coat’ from an aerosol or a thin wash-coat of colour. This will highlight low patches in the final rubbingdown session. For this, use P400. Correct any surface defects highlighted and repeat for that local area only. Finally, apply the top-coat. Two coats should be enough, though this will depend on the paint you choose to use and how much you thin it.
The epoxy primer can have any kind of paint applied on top of it. You can use traditional coach enamel thinned with white spirit, but we’ve recently had a very good experience brush-painting with MIPA singlepack acrylic. It needs its own thinner, or at least a universal non-cellulose thinner.
While enamel’s applied in a relatively thick slow-drying coat, the acrylic coat is much thinner and dries quickly. It flows
Sam Glover TECHNICAL EDITOR Sam has broken down in a gigantic variety of classics over the years, then worked out how to fix them.
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out freely but the fast drying means it’s less prone to run or sag. It’s also very densely opaque, even in a thin coat.
The epoxy primer is impervious to water, so the job can be paused indefinitely at the primer stage. Nonetheless, water can be attracted to the surface and will result in microblistering of the top-coat if it gets painted over. To this end, the body must be warm before applying further paint.
All rubbing-down is done dry to stop water absorption. Non-clog abrasives such as Norton Mesh Power or Mirka Abranet are meshes coated with abrasive compounds. They generally need a special sanding block with dust extraction, which makes for a dust-free working atmosphere and prolongs the working life of the abrasive. You could improvise a dust extraction system using a vacuum cleaner.