Bumper Cover Material?

[racerstev]

I'm getting started on a respray for my tatty Elan. The car has been resprayed in the past with rather poor results.

I started the project on the front bumper working at first on the chipped areas. Seems the paint did not
adhere to the bumper very well, I was able to peel almost all the paint off with a heat gun and a little
elbow grease. The paint came off in long wide strips like peeling tape off a roll. Clearly the bumper wasn't
prepped correctly before painting. Does anyone know what material the bumpers are made of so I can buy the
proper primer and adhesion promoters?

Thanks in advance Steve

[Jeemy]

As far as I know its fibreglass or GRP and needs a gelcoat before paint will stick to it. I don't know the specifics but thats my understanding.

[hodge]

There's a front bumper repair and paint write up in the Wiki listed under paint repair, it mentions an 'adhesion promoter aerosol '.

[chrisP]

Unless you have a fiberglass copy of a bumper (some companies have made them) then the actual structure is:

Flexible reinforced polyurethane ........ material bonded to a stiffening and shock absorbing composite armature

I have an original bumper I am stripping off the paint and I was surprised that the original lotus paint does not bond to the underlying primer, I can 'ease' large patches of paint off with a scalpel

Chris

[Brit-Car-Nut]

You can thank GM for the paint and plastic choices.

For people in the US, the materials are common in most modern GM cars, so following GM processes will result in the best finish.

I don't know what the other manufactures use for their bumpers, so they might use a different solution.

A lot of additives and paint systems used in the '90s are no longer legal to spray so unobtainium, so the best solution is to ask your professional paint supplier for the matching primers and additives.

[Jeemy]

The back of my UK car bumper looks so much like fibreglass that I was sure it was that. If there is a polyurethane outer on the front, then its simpler to my knowledge, any high-build primer will fix problems, but a flex additive-containing one is best.

You need to be careful sanding the poly, if you bite into the original urethane coating, it will get very textured very quickly and be hard to make smooth.

Urethane-specific primer, base coat and paint are available; but how to match the paint to the remainder is more difficult.

My car has had a full respray with high-build flex primer, gelcoat, 6 coats of paint and 3 of lacquer. The manufacturer was U-POL and the products I bought were called reface, priming gelcoat, paint and high gloss lacquer. We mixed the paint with a glitter additive called Gemini, it was 2-pack paint.

This worked perfectly on the bumper although the 15-min drying time for the lacquer meant some dust take-up which a lot of minor correctional work will be required for. On the clamshell and top rear shell, stress cracks in the original material are coming back through the paint. All I can do is go over them again and as yet I do not know what the issue was preventing these from being sealed off in the priming process - painters' slackness most likely. He has promised to make it all good but I'd do as much research as I could before respraying to try and avoid the issues I have had and a pro paintshop (I used a local guy who is cheap and cheerful) will probably know and happily impart the advice freely.

[chrisP]

Jeemy, the cracks will come through the paint regardless, pretty much the only option to fix it is to go right back to the base of the panel, repair with glass fiber tissue (or similar) and then build back up the paint. I'm going through the process on my car at the moment.

Chris

[racerstev]

.

Unless you have a fiberglass copy of a bumper (some companies have made them) then the actual structure is:

Flexible reinforced polyurethane ........ material bonded to a stiffening and shock absorbing composite armature

I have an original bumper I am stripping off the paint and I was surprised that the original lotus paint does not bond to the underlying primer, I can 'ease' large patches of paint off with a scalpel

Chris

That's the same here, the gray primer stays put but the paint peels right off. A little heat allows you to pull
it off in sheets.

It's looking like the bumper cover is a polyurethane just like other early 90's GM cars. SO with that in mind I'll be trying this to help
it stick to the original primer and the bare poly


http://www.eastwood.com/gray-urethane-p ... twood.html

and

http://www.eastwood.com/epoxy-primer-wh ... t-kit.html

I guess the epoxy provides the adhesion and the primer provides the flex ability and ability to
fill pin holes.

Steve

[Jeemy]

Going to be difficult for me to do that due to the specialist paint used. I know in my heart you are right.

Technically going back and painting a bigger area is no different to blowing over a smaller, and one can argue that the ability to feather and blend the repair gets easier the larger it is.

However these are really not that visible. You can't see them from more than a metre away. Not to my standards, sure, but acceptable I guess. And this has been 4 months now, 2 spent outside, 2 inside in varying temperatures from -3 up to 20C.

I am fairly confident the paint has had enough time to cure and that a blow over is my fix for now. They haven't got worse and they haven't broken the existing lacquer coat, they are just peeking through.

I am trying to remain jovial about it but was pretty heartbroken when it started happening. I did sand them away but not completely away before painting and pointed them out to the paint guy. I think he decided it would be all right on the night.

This is why I will do my own painting from here on in.

[chrisP]

Jeemy Good luck with sorting the lines/cracks out. I'm stripping the paint off my car completely ready for a respray and I'm quite amazed at the number of repairs I will have to make to the fiberglass, it really isn't that resistant to flex and stress. I'm reinforcing with epoxy fillers and carbon/epoxy matting and then re gel-coating

Chris