Audi A3 - Undersill paint flaking - Hopki

Some of the paint on the undersill (passenger side) of my 2002 A3 has started to flake off. Does anyone have any tips re how to treat and protect? I imagine the area will need rubbing down, treating and re-painting.

Thanks

Audi A3 - Undersill paint flaking - Ethan Edwards

If it was mine. I'd lightly brush the area with a wire brush to remove any loose material.

Then I'd inspect for any rust. Ifany is present sand only htose areas down to bare metal (ish) treat rust with stuff bought at Halfords eg Kurust or something along those lines.

The one I have turns black when it dries, ask the teenager behind the counter.

Then quick spray over the now non rusty areas with acid etch primer (masking off bits you don't want primed). Then I'd apply two generous brushed coats of Black Hammerite....or any colour you like really. Don't buy the spray version it goes everywhere. This could be all you need to do BUT.....

Use an old throwaway paintbrush for the Hammerite as it's a swine to get out.

If any treated area shows much from the side I might then the next day very lightly rough up the surface with some very fine sandpaper and once you wipe the surface with a clean white cloth (dampened with meths - allow to dry) spray the body colour on as a topcoat purely for cosmetic reasons. Should cost you no more than a weekend and oohh say £20?

Should last several years.

Hope that helps, but someone may have a better treatment...thats just what I used to do to my old Princess.

Audi A3 - Undersill paint flaking - 659FBE

VAG bodies are electro galvanised and any abrasion will remove this - definitely not recommended.

I have played about with rust prevention treatments over the years and have found what I consider to be an unorthodox but highly effective treatment. The essence of this is that to some extent, in real life you are dealing with partially rusty, dirty and probably damp metal. Therefore, any paint won't work.

A wax based treatment is effective and my tests have shown Waxoyl to be completely useless. A product marketed as Dinitrol in the form of a liquid (when warm) brown wax is brilliantly effective. On a sill, it requires mechanical protection. Although over-covering of Dinitrol is not recommended, I have found that if you let the solvents evaporate for several days, the Dinitrol is hard enough to accept a covering of Tetraseal black bitumen based underseal.

You will obviously not achieve strong adhesion on a wax based "primer" but this is not a primary consideration here. The bond is strong enough to last in wheel arches and on sills.

Dinitrol is a fairly expensive, and highly effective rust treatment.

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Audi A3 - Undersill paint flaking - Ethan Edwards

>VAG bodies are electro galvanised and any abrasion will remove this

..and if there are some rusty patches present already? You'll need to remove the rust since the Galvanising would have already failed.

A light wire brushing to remove the loose material (if done carefully) will not cause any abrasion through to the metal but IMO whatever you decide put on to a surface, it cannot be appled to what the OP described as a 'loose and flaking' surface.

Audi A3 - Undersill paint flaking - 659FBE

The beauty of the Dinitrol brown wax is that it can be applied to a "loose and flaking" surface. It provides outstanding protection aganst further rusting if it is applied to a rusty surface. When applied warm, its low viscosity allows it to penetrate seams and spot welds and the evaporation of the solvent then leaves a hard wax layer.

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