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Topic Review (Newest First)
12-21-2007 09:54 AM
there are products made for urethane stripping the one i use is in a aerosol can, mar-hyde produces it and also kleen-strip(bulldog)and i have never had any issues with it.
and there are plenty of us ASE cert guys out there and our opinions well you know how the line goes.
any advice jc and bondo king give you is golden. they are also LIL members.
02-05-2006 09:07 AM
Preping bumbers and Plastic parts

First off DO NOT USE strippers as everyone stated !!!!!!!
Next use 120-220 grit to DA the parts or have them media blasted, 80 grit
will leave you with a mess that you will wish never happened. Any primer that is flexible can be used so long as it will work with your paint system. But you must use flexible primers. You also need to watch out for parts that where primed with a WATER BASED PRIMER this was started 20+ yrs. ago as a eco friendly try. The water based is still in use today on some parts. The last thing is you MUST USE FLEX AGENTS IN YOUR PAINT!!!! It DOSEN'T WEAR OUT OR FADE AWAY. I have used it on Vettes to stop the spider webs from coming back and it works even better on bumbers and plastic. If you want to see what happens to a bumper without flex just look at cars in the mall with little bump on the bumber, you will see chip and large cracks.
And for what is worth I am an ASE Master auto body tech. along with Dupont & Sikkens paint schools + 34yrs of collision & Retro work.
Good luck and I hope all goes well on your project.
02-05-2006 12:34 AM

One of my businesses is reconditioning plastic bumper covers. Never use a chemical to strip the color coat and clear or you will end up in trouble sooner rather than later. You only need to strip the clear to get a primer onto the paint underneath. Strongly recommend that you strip the clear with a DA sander starting with #120 so as not to leave any scratches, then to #180. You have to get every last bit of clear off or it will flake the paint, so you will also have to do a bit of hand sanding. Remember, it has soaked of years of wax. Get a plastic razor and tube of pin hole filler to fill the inevidable holes which appaear in the plastic. Give it a thick coat of Transtar 1225 or some other hi-build primer, then detail it again, and givve it a final coat of hi-build. Like painting metal, prep is everything. Spray your paint. We never use flex coat because bumper covers don't flap around like they used to, which produced the cracks. Clear the paint and mount the cover. The fun thing about plastic is that you can weld pieces of different covers together with fog light openings, ducting or whatever quite easily so that you are not stuck with a factory cover. Harbor Freight sells a decent cheap kit and rod that can get you started. Just remember to use the same type of plastic -- they cant be mixed. Reshaping plastic is also easy with a little patience and a heat gun. Good luck.
02-02-2006 03:35 PM
starquest Thanks for all your help!

I tried the aircraft stripper on a small plastic part and it did indeed seem to melt the plastic. It didn't destroy the part but it seemed to weaken the plastic a bit, to the point where if you weren't carefull with the putty knife that it would cut into the plastic with ease. But once washed off good with soap and water and dried, it hardened back up. Anyway, I think I'm going to stop using the aircraft stripper and try the stuff mentioned above.

Also, I believe the consensus is to continue use of the SPI epoxy and SPI 2k without a flex additive.

Thanks for all your help,

02-01-2006 05:08 PM
x711 Jc,

Thats right on the Money man.

Good post !

thanks .. X
02-01-2006 07:44 AM
jcclark The thing to remember about flexibility, it's a time issue.
All things will harden eventually, it may take 100 yrs, but eventually.
I have had some clears stay flexible for a couple of years then
get brittle, so how much time is enough for a test?
And how much is acceptable?
I usually guarantee my paint for three years. That's what I shoot for.
I have redone some other body shops work that took that long to show up.
Especially blends, where the clear started to show differently.
My own "test" paint job with "Lazer-Dry" looked perfect for 3 yrs,
then went bad quickly.
That's why it's important to remember that just because the paint looks
perfect after being done or a couple of months doesn't mean
it's a really high quality paint job. Time has to pass.
There have been girls and guys on here giving advice about their own high
quality paint jobs and only started painting a year ago. That's not enough.
The real test is time, and for me the three year period seems to reveal
what really has been done.
So if you want to check flexibility or adhesion, I want to see it on
something at least a couple yrs old, then we'll know.
02-01-2006 03:56 AM
adtkart Bob... Since I work in a shop where we replace alot of bumper covers, I am thinking about bringing some small bumper pieces home from work to test. That stuff really sticks to everything, so I want to do some tests for the flexability, and really test the adhesion on them too.

01-31-2006 09:16 PM
baddbob Aaron, Isn't that SPI epoxy some amazing stuff? I did some flexibility tests on steel panels with bending them 180 degrees and couldn't get the stuff to fracture, this was after a four week cure! Bob
01-31-2006 07:56 PM
adtkart I have a mixing cup in my garage that had SPI epoxy mixed in it. I have tried to get the stuff out. I have definately tested the flexability of the stuff there. I sure don't think it needs a flex additive in it.

I would go with the SPI epoxy on a bumper cover at any time, infact I am in the process of that right now.

01-31-2006 03:35 PM
roger1 Captain Lee's Auto Spra-Strip is what is recommended for fiberglass Corvettes.
I just used it and it dissolves the paint but not the primer. And the Corvette I just did was a '69 and it still had the factory primer on it. So it didn't even get to the fiberglass. I sanded the primer off afterwards. That was still a lot easier than sanding off the 2 layers of paint that were on top.

It is not supposed to eat into fiberglass at all.
Don't know about using it on urethane or plastic parts though. But if it doesn't go thru the primer, it should be OK on that too.

01-31-2006 02:59 PM
x711 Kevin,

The 5425 primer has the flex additive built in, "You do not have to add it"

I mentioned this because you do not want to use primer on a flexable part
such as a bumper cover etc that could possibly chip away or crack if the
part was flexed etc. Keep in mind, Paint goes over the primer. If the primer
cracks or breaks away.. So will your paint !

Thanks.... X
01-31-2006 01:00 PM
jcclark I know that I don't know, you know?

I haven't used the flex agent in a long time and the bumpers
I've done have held up just fine.
My daughter has tested the flexibility out on steel panels for me,
(she smashes something regularly) and the paint has stayed on
amazingly well. So I'll keep painting without it.
01-31-2006 12:07 PM
BarryK The older flex agents did lose effectiveness over time.

If the flex agent uses "Polyglycidyl Ether Polymer"
(Excuse spelling as I don't have access where I'm at.)

This additive is a plasticizer and will remain flexible, only problem is its not required to be listed on MSDS or Label so how you will know, I don't know.
01-31-2006 11:13 AM
jcclark I do a lot of bumpers and I usually use stripper, I haven't had one melt
yet but I'm careful as I go to watch the progress.
Some of todays bumpers have so many little openings and grill work that
I don't see how it would be possible to sand all the paint away.
I have had some "fuzz-up" from sanding when dry sanding, so I avoid that.
Usually after stripping I wet sand the whole thing with 400 just to remove
all the residue from the stripper.
Some people don't prime bumpers before painting, they just apply a coat
of "Bulldog" adhesion promoter and paint. I'll do that for small sections but
for a complete bumper I still like to prime with a good 2K.
With the "el-cheapo" bumpers I usually paint I need the 2k for smoothing
out the imperfections that they're known for.
01-31-2006 10:59 AM
jcclark This is a quote from another forum on flex additives.
I think we've been misinformed on here.
The mfg's says it is permanent and keeps the paint softer.

"I used to believe the same thing, because sooooooo many people will tell you that flex will 'wear out' of the paint and it's only temporary. Many times they'll add something like 'just phone the manufacturers and they'll tell you the same'. So a while ago I did just that, I phoned dupont and asked them if flex was only temporary. THe guy sounded a bit like he had never even heard of that before, and of course it's not temporary. It lasts, it's permenant, the paint won't return to "original hardness". Just phone the manufacturers and they'll tell you the same!"
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