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Dealing with rust and possible filler.

Dan Cook

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Hi all,

I am currently dealing with some rust on my car. I have some bubbling paint around the weel arches. My intention is to take back to metal, use rust treatment, prime and then paint.

While I was doing that I thought I would takle the back of the car under the back bumper, this has always had a rough texture. When I started sanding, I have this dark material. I was wondering if this is some kind of filler. Also whether I sould keep sanding and the treat like the rest of the car of whether I should be looking to put something back on this part of the car before painting.

Thoughts anyone

Thanks in advance.




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I wonder if that's stonechip? A thicker rubbery kind of paint, more resistant to stone damage, sprayed over vulnerable parts of the car. I've used it in wheelarches. Some of them have a textured finish. If you need to, sand flat, and overpaint - it's probably cellulose-based from a can.

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I take it that's a GT6 Mk3?

The easy bit to answer is the black stuff on the rear valance. That is Stone Chip Protection. Commonly called 'Stone Chip' or 'Gravitex'. Used properly, for example on sills ends, under floor pans or wheel arches, it offers durable protection against, errr.., stone chips. Used improperly it is a cheap and cheerful way of disguising dented, ill repaired or rust-scabby bodywork. If it's known that the metalwork underneath  is sound it can be flatted off a bit, given some primer and then refinished in body colour. But there is a distinct possibility that it is there to disguise corrosion problems: What lies beneath can only be found the stripping to bare metal, but removing stone chip can be a long and tedious process  involving twist knot brushes, DA sanders, heat guns and graft.

Bubbling wheels arches is a tricky issue. Wheel arhces generally rust from the inisde out. What may look like a minor scab on the outside can be the iceberg tip. Photo attached show how a 'few bubbles' became a major repair on my wife's Copen. In this sort of situation only a welded repair will provide any long term durability. The alternative is to patch up as best possible with fibreglass or filler. May hold up for a couple of years or so but ultimatley a 'proper' reapir will be needed. If one has to make a bridging repair of a rust hole then a fibreglass repair paste (e.g. p40) is preferable to a ordinary body filler - fibreglass is waterproof whereas standard talc based filler soaks water up and readily becomes a soggy pudding.


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Thanks for this Chris and the detailed advice offered, this is very helpful. I have sanded the wheel arches and they are looking in pretty good shape, will still treat them with rust treatment. I will see what I can do about the rear valance of the car.

The car is a Spitfire 6.



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