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Paint stripping a rear spoiler

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  • Myotherapy
    replied
    Originally posted by pmonsour View Post
    Does anyone have experience trying to paint the rear wing???

    I am at the end of my rope. Been sanding and priming it over and over and cracks come out. before I sanded it there were ZERO visable cracks. now there are 2 lines from edge to edge, and cracks in the middle. Sand it prime it, then 30 min later the cracks show again. Not understanding what is going on when there were no lines or cracks before we started sanding it down for paint?

    any help!?!?
    Yes I have just sanded mine back. You will most likely still see spider cracks in the black rubber. Use wet and dry paper about 400 grit and try and rub these hairline cracks out as well as possible.


    Then apply Polyester Hi build primer. it sets like concrete and wont re-crack. If you can still see the spider cracks after the hi Fill has set, cut the hi fill back (not right through to the rubber again) and give it another coat.

    Sand the hi build primer back until its nice and smooth. the smoother the better the final outcome. then make sure you clean the surface very very very well with paint cleaner.

    Then spray it in your chosen colour.

    remember the more pedantic you are with preparation the better the finish will be and quality of your work.

    Sand with a very fine grit 1500-2000 grit, to get any orange peel or rough spots off. then polish with a buffer and presto.
    Attached Files
    Last edited by Myotherapy; 07-27-2013, 10:36 PM.

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  • sportevo452
    replied
    also a good idea to let the primer and paint air dry and not to bake it.

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  • nsubre
    replied
    Hi,
    The paint and primer the factory applies to the rear wing is made for steel. With the rubber under the stock wing, the steel primer is wrong, and that is why you get spider webs in the paint eventually. So you should remove all the paint and white primer, down to the black rubber layer, and then use Featherfill primer, which is made to go on fiberglass instead of steel, and paint that. You won't get any more spiderweb if you do that.
    Larry

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  • pmonsour
    replied
    Thanks for the help. it is a pain. a bad one at this point. Got with the Paint shop and they gave me the right primer to use. almost done painting the car, and this along with the front, rear, and side pieces are all that are left.

    thanks for the advise

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  • Mario L.
    replied
    Rear wings are covered in a rubber based membrane, and must be stripped bare for refinishing. I suspect your issue is from the primer, possibly out of a rattle can?
    Maybe your sanding exposed a lower layer of paint?

    Seek out a paint professional for good results, these things are a PIA to refinish.

    Mario L.

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  • LeeVuong
    replied
    The long shape of the wing as well as the flexible rubber structure beg for some flex agent in the paint.

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  • pmonsour
    replied
    Does anyone have experience trying to paint the rear wing???

    I am at the end of my rope. Been sanding and priming it over and over and cracks come out. before I sanded it there were ZERO visable cracks. now there are 2 lines from edge to edge, and cracks in the middle. Sand it prime it, then 30 min later the cracks show again. Not understanding what is going on when there were no lines or cracks before we started sanding it down for paint?

    any help!?!?

    Leave a comment:


  • wld_tony
    replied
    True, i just brought in an M3 from Japan with an oem EVO 3 poiler, the core of the wing is cardboard then a layer of fiberglass then rubber, It had spots on parts of the edge that had paint cracking and that was the result of the rubber flexing, Soft rubber......

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  • UNHCLL
    replied
    Originally posted by LeeVuong
    The Evo3 is made from thick mushy rubber as the big rear spoiler found on the 1979-1980 Euro 635. I will post picture tomorrow.
    I don't think so??

    If you strip a stock wing, its a rubber outter layer, with the carboard honeycomb inside. I've cut a stock wing and half, thats why I know 100% what a stock wing is.

    As for the evo, I'd wager its similar...? Rubber outer layer, composite/cardboard inner?

    Definitely post pictures. From the initial look at the outside, they do appear to be like the M5/M6 rear lips.

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  • LeeVuong
    replied
    The Evo3 is made from thick mushy rubber as the big rear spoiler found on the 1979-1980 Euro 635. I will post picture tomorrow.

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  • UNHCLL
    replied
    The core is corrugated cardboard on a stock wing. I can't speak 100% regarding the evo wing, but I'd wager its the same.

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  • LeeVuong
    started a topic Paint stripping a rear spoiler

    Paint stripping a rear spoiler

    I ended up with an OEM Evo 3 rear spoiler, for free. The spoiler was white and had a few long cracks. In the center, and at each end. Probably caused by some flex, not the usual contraction/expansion. Having nothing to do this weekend, I decided to strip it from its paint and see how come that sucker was so heavy, and what caused the cracks. I bought two quarts of furniture paint stripper, a small horsehair brush and here we went.

    I first removed the flipper from the main wing and generously apply several coats of stripper on the main wing. After the second application, the first layers of paint started to peel off byt them self, without requiring any work from me, except laying more qand more stripper until I reached the final coat. There were 4 coats of paint (and 4 coats of primer). I let the paint finish flaking and harden overnight. I stripped the flipper, layer per layer, used a razor blae to remove some of that extra hard gelcoat, softened by the stripper. With some running water and hard scrub, I finished removing any paint and primer stuck on the flipper. I little bit of 600 grit and water finished cleaning up the flipper. He is how I spent 4 hours of my day.

    It was instructional as I finally understood what was that "fiber reinforced plastic" the flip is made from. Imagine a dark resin, withy full of white hair. The flipper is now ready to be primed and painted. I even managed to leave the part number and logo untouched. Just like new.

    The second day, I went back to the main wing and sanded it with an electric sander and some 220 grit. The paint that is usually tough to remove is now extremely brittle and flaky. I spent the 3 next hours removing whatever paint was left, with some water and a block sender, leaving a perfectly smooth finish. The main wing is very soft when yo press it. Right in between rubber and plastic. It is black all around, but the under part is a clear "fiber reinforced plastic" in wich 16 inserts have been cast. I do not undrstand why BMW who was dealing with shops like "Die Weithje" could not come up with a much lighter composite rear wing. If you have ever weighted a CF rear wing from MA Shaw or any other supplier, it is feather light, so much that the trunk opens by itself...

    The reason why those rear OEM wing crack all the time, is propbably because the core itself is soft. Add 20 years of contraction and expansion, half a dozen of stiff paint coats, and you have a recipe for major cracks. In my case, the paint had badly cracked, but the core itself is perfect. I spent all in all 7 hours doing the job, prepping the wing so that my bodyshop can put a sealant, milk coat it and paint. I saved them the kind of job they hate to do, and I made sure it was done perfectly. I hate when coats of paint accumulate, as it makes a opart brittle and easy to chip. Picture of the stripped wing soon.
    Last edited by LeeVuong; 10-14-2006, 12:46 PM.
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