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Old 01-18-2010, 03:04 PM
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Urethane bumpers!

Can somebody give me some advice on sanding and priming urethane bumpers. I have a 3m automix kit to do all the repairs but what do I need to use as far as sand paper grit to sand to rest of the bumper. I am going to put 3 coats of 2k primer on all the sheetmetal would it be a good idea to hit the bumpers with 2k as well or just color coat them after repair. I have been holding off and waiting till the end to do the nose and rear bumper because I was unsure of the process. Any help would be greatly appreciated. Thanks, Jason.

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Old 01-18-2010, 04:25 PM
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Do not use that 2K primer on the bumpers. It will not adhere to it.

To paint those bumpers you need mid-coat adhesion promoter, that,s all. Then paint them.
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Old 01-18-2010, 07:12 PM
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Any suggestions on product brands.
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Old 01-18-2010, 09:08 PM
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It doen't matter. Dupont or PPG will both work the same.
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Old 01-18-2010, 10:21 PM
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I use Bulldog for a adhesion promoter, and a flex additive in the clear when doing bumpers.


Bulldog comes in a rattle can and can be purchased at a lot of auto part stores, and I think it works well.

Flex additive varies depending on the clear brand you are using.

If you want to cover a black bumper before spraying a (lets say) gold base, I just use white base and add a little black to gray it up a little, and I spray that on to cover the black before I put the gold base on.

I wet sand the bumper with 600.

I use a wet red scotchbrite pad and give it a once over while getting the nooks and crannies.

I dry the bumper with some paper towels.

I use glass cleaner to clean it off the residue(wax and grease gives me fisheye problems on bare plastic bumpers)

Blow off the bumper to make sure no water is hiding in a nook or cranny.

Tack rag the bumper to remove dust.

Bulldog, two medium coats spray five minutes apart, (don't run it, medium to light coats)

10 minutes later I'll tack it off again.

(For Gold Or Silver base coat application I use the following steps)
Spray the light gray (non metallic) base coat, usually takes 2 coats to get adequate coverage, make sure first coat is flashed completely before spraying the second coat.

Then wait for that to flash off, tack rag it and start your gold or silver base, usually 3-4 coats for those colors.

Let the base flash off completely, I usually wait 10-15 minutes depending on the temperature and airflow in the booth or garage.

Mix your clear and add flex additive, it's usually a cap full per pint but read the directions before assuming.

Then clear, 2-3 coats.

Make sure you get the edges of the bumper that face the tire, a lot of people miss those.
So prop up the bumper high enough so you can get your gun under those edges to paint.







Edit* I just saw you were repairing a bumper...

Repair the bumper by grinding the cracks all the way through, you want to "V" out the cracked area so your product can adhere to it better, if you try and glue a crack together without "V" it will usually not hold.

Once repaired I will use a polyester glaze to even things out, now I must warn you this is not recommended, but I have never had one crack out on me yet, then you can buy a flex primer in a rattle can from the auto parts store, I like the flash time of rattle can flex primers over mixed spray gun primers with flex additive in these applications, it seems to feather out better too.

If it's a gold or silver you are going to want to spray a clear sealer down so the metallic flake lays down evenly on the blended areas.

Last edited by cutterbond; 01-18-2010 at 10:38 PM.
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Old 01-18-2010, 10:26 PM
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Flex additive is an option. You don't need it when painting urethane bumpers.
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Old 01-18-2010, 10:46 PM
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Quote:
Originally Posted by cjperotti
Flex additive is an option. You don't need it when painting urethane bumpers.
If its on that car in his avatar he will.
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Old 01-18-2010, 11:09 PM
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Out of all the bumpers I have done urethane bumpers (yellow in color) have been the hardest I have used the flexible fillers and have had it crack so I weld all scratches and sand smooth with 180 grit on a D/A and prime with a flexible primer then before painting apply 1-2 coats of adhesion promoter
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Old 01-18-2010, 11:45 PM
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Quote:
Originally Posted by cjperotti
Do not use that 2K primer on the bumpers. It will not adhere to it.

To paint those bumpers you need mid-coat adhesion promoter, that,s all. Then paint them.
If he is repairing them, he will need to prime them.

Surfacer DOES stick to plastics...it happens every single day is body shops all over. The key is cleaning the plastic well, and using an adhesion promoter before laying down the primer.

And if as said, if it is the bumpers in your avatar, not putting flex agent in would be silly, especially if you have the bumpers off.
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Old 01-19-2010, 03:12 AM
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Personally I would paint the bumpers on the car after edging what needs to edged. Primarily because I donít like risking parts being damage during installation. But, maybe thatís just me.

When I posted flex additive is an option, I was being polite. If anybody here was ASE certified or studied for the ASE test they would know those question would be specifically asked and the correct answers would be no flexible primer would be required on a repaired urethane bumper and no flex additive is needed in the urethane clear. Evidently no one here is ASE certified.

There is a reason products like flex additives, flexible primers, etching primers, Velva seal and sealers in general are produced. Theyíre produced to meet a specific market. That market is the technician that doesnít know what heís doing but thinks he doeís. That market is huge and brings in a nice tidy profit. You guys fit in that market.

As you can see Iím tired of being polite. You obviously canít do a car without resorting to exotic products to assist you. Too bad.
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Old 01-19-2010, 08:23 AM
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I've only used a flex additive for paint once In 35 yrs,IMO its not necessary.The procedure for repainting a painted surface is the same whether its plastic or metal makes no difference.A couple light coats of 2k primer over the repair is all thats needed (not three coats)... sand with 320,scuff the tight spots with a scotch brite.adhesion promoter is a good idea over old paint especially where you only scuffed.not necessary over the repair.I use bulldog myself or dupont 222.it also helps on new bumpers that are primed after scuffing.
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Old 01-19-2010, 09:25 AM
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Quote:
Originally Posted by cjperotti
Personally I would paint the bumpers on the car after edging what needs to edged. Primarily because I don?t like risking parts being damage during installation. But, maybe that?s just me.

When I posted flex additive is an option, I was being polite. If anybody here was ASE certified or studied for the ASE test they would know those question would be specifically asked and the correct answers would be no flexible primer would be required on a repaired urethane bumper and no flex additive is needed in the urethane clear. Evidently no one here is ASE certified.

There is a reason products like flex additives, flexible primers, etching primers, Velva seal and sealers in general are produced. They?re produced to meet a specific market. That market is the technician that doesn?t know what he?s doing but thinks he doe?s. That market is huge and brings in a nice tidy profit. You guys fit in that market.

As you can see I?m tired of being polite. You obviously can?t do a car without resorting to exotic products to assist you. Too bad.


LOLOLOL, there is no reason to get huffy. The one thing people forget on these forums is that sometimes the written word isn't everyones forte and even if it is, we still sometimes write something that comes out wrong on the other end. If we were all sitting in a garage having a beer and chatting any little bump would be gotten over in a minute and no big deal.

Don't hang too much on the ASE tests, I have taken and passed MANY of them from paint and body (got 100% on the paint one) and mechanical being a "ASE Master Technician". Of all the testing and classes I have taken ASE are the least valuable. They are still good, don't get me wrong. But they are TERRIBLY basic and even outdated. There will be things like lacquer questions still on the test!!! Or plasma cutters, they talk about them like they are the up and coming thing that will be in every shop. This was obviously written about 1990 at best.

So don't be taking all that ASE stuff to heart.

You are very right that flex additives are out of date, as I know of no products that need them. Using a flexible primer on the bumper IS a good thing, but they come pre-packaged with no need for adding anything. Adhesion promoters, yes they are a good thing, but ONLY over bare plastic as your paint or primer going over paint and primer doesn't know what is under the paint or primer, right? If you wouldn't use adhesion promoter on a metal fender that has primer on it, why would you use it on a plastic bumper that has primer on it? So I certainly see your point.

But on bare plastic, as recommended by manufacturers an adhesion promoter is a good idea. But yes, do leave the flex additives at the paint store for someone else.

Lighten up, it's all good.

Brian
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Old 01-19-2010, 11:52 AM
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its was always my understanding adheasion promoters were MADE for painted surfaces that are tough to sand properly ,like louvers and such but also work on primers and plastic.
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Old 01-19-2010, 12:08 PM
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Quote:
Originally Posted by deadbodyman
its was always my understanding adheasion promoters were MADE for painted surfaces that are tough to sand properly ,like louvers and such but also work on primers and plastic.
Products like Dupont 222S was that product, but I didn't even know it was still available! It was a lacquer product and no very good at all compared to todays products.

But plastic adhesion promotors like Bulldog are for plastic, that is it. If something is sanded properly no more addhesion is needed. But on plastic that is a whole different story. Between "self healing" properties and solvents gassing out of it and all kinds of stuff, the promotor DESIGNED for plastic does wonders.

Brian
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Old 01-19-2010, 01:10 PM
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sure, its still around I just got a qt. . I actually prefer it to bull dog(the aerosol kind) but 222 is for all paints especially on burns and blends where the transition from gray scotch brite goes to unscuffed paint and always where I my blends end and its only got gray pad scuffs.I never knew bull dog was made for plastic and 222 was for lacquer....its been working fine for years I always thought adhesion promoter was for paint,to chemically soften it up and allow the new to stick to the old better. I guess I gotta go check out the ingredients in both, They smell the same,but this is how it was explained to me years ago....I never read the ingredients.You got me curious now ,Brian.
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