Problems Painting Brand New Bumper Cover

[jmd_forest]

I am having fits painting a brand new bumper cover. Started by scuffing with fine scuff pad and then light sanding with 400 grit with soapy water. After thoroughly drying, applied 2 coats of an adhesion prompter (Bull Dog) , per discussions with manufacturer. Manufacturer didn't say Bulldog, just an adhesion promoter. Unfortunately the Bull Dog ran because I had the gun set up for 2K primer and I didn't set it up for the Bull Dog.

After letting it dry overnight, I wet sanded it out with 400 grit and soapy water, thoroughly dried, and applied 2 light coats of Bulldog, flashed for 5 minutes, and applied a light coat of 2K high fill primer. The primer crazed first at the edge of anywhere I sanded through the first BullDog coat, and by the time the primer dried, all over the place.

My current plan is to throughly strip the bumper using "bumper/plastic stripper" and repeat. This is absolutely crazy (no pun intended). Any Ideas of what went wrong or what I'm doing wrong?

Note: I am not a professional painter (obviously) but I've successfully painted a dozen or so cars in the last 20 years.

Any, any, any, ANY help would be appreciated.

jmd_forest

[Cecil Beach]

Hello JMD,

If this is a brand new Porsche bumper, it has a gray coating on it and you probably don't want to strip it. Check with your local paint store and purchase a water borne primer that will give you a protective coating. That coating will provide you a protective coating to paint over.

Cecil

www.bodystylebycecil.com

[jmd_forest]

Cecil,

Thanks for the reply.

Bumper is an aftermarket bumper for a 2007 Lexus, via the internet. It came as raw black plastic, and to the best of my knowledge, it had no factory applied adhesion promoter, as "confirmed" by my discussion with the vendor's paint shop to apply an AP (sorry, my post above said manufacturer).

I did already strip the cover using Bulldog plastic bumper striper and it is back to raw plastic, as far as I can tell.
Unless I get advice otherwise, my plan is to reapply bulldog and primer, wet sand the primer, and then the 3 stage finish coat. The reason for the primer is to color match the fenders and hood that are also being painted and are already primered in a color that matches the 3 stage finish base coat.

Funny thing is, I gave the back side of the cover a quick spray of bulldog and primer and it stuck just fine, no crazing. There must have been something on the surface that didn't come off with a quick wipe of reducer followed up by the scuff and soapy 400 grit.

My paint vendor said they don' carry water based paints.

I think I'll wait a few days before starting to see what the forum has to say before doing anything more.

Thanks again for the reply.

jmd_forest

[jm529]

jmd, i've used bulldog for years on many cars and never had any problems. make sure you read the instructions on the can. when you say the primer is crazing, it usually means that its lifting the bulldog up off the bumper.

did you allow the 2 coats of bulldog to dry at least 30 min before you started to primer? i'm guessing that the bulldog was still wet when you sprayed the primer. make sure you mix some of the bulldog with the primer, it's also a good flex additive.

[jmd_forest]

jm529,

Thank you for your reply.

By crazing I mean a million tiny cracks in the primer where the black bumper showed through the crack. The bulldog goes on clear so I don't know if the cracks went through the bulldog or just "to" the bulldog. I followed the directions (as I understood them) ... "2 to 3 coats. Allow to flash 2 -3 minutes between coats". For "New flexible and rigid bumpers" the can does not give instructions for flash to color coat (in this case primer). I allowed only about 10 minutes to flash before the primer coat (but is was cold in the garage about 50 degrees) because for overall refinishing the can says allow 10 minutes to flash.

I'll allow 30 minutes before I apply the Primer and will mix in some Bulldog.

Good thing I bought the quart and not the spray can!

jmd_forest

[jmd_forest]

It warmed up to the 50's today so I thought it would be OK to primer the bumper cover. I warmed up the garage a touch and shut off the heater. Cleaned the gun real good and shot a light wet coat of Bulldog. It went on just a hint wet wet and clear. Let if flash for 1/2 hour while mixing up the 2k primer. Added about 10% Bulldog into the 2k and just a capfull of urethane reducer to thin it out a touch since it was coming up a little dry on my test panel.

Shot 1 light 2K primer coat, let it flash for 15 minutes and them 2 "light medium" coats with about 15 minutes of flash each. The bumper cover came out beautiful and smooth, no crazing of any kind.

Letting it dry for the rest of the day (about 8 hours) and will 400 grit wet sand it tonight in prep for real paint tomorrow.

Its supposed to be in the high 50s here tomorrow and I'm hoping to shoot the 3 stage on the 4 panels (hood, 2 fenders, and bumper cover) so I can finally get this car finished.

Thanks for the help gentlemen

[jmd_forest]

Well.....All went well except for the picture below. I have NO idea what went wrong

The "crack" happened after first pearl coat. This picture taken before clear coat. I figured I'd just push through and then sand out and patch up the spot after everything cures. Actually, this is not a run or a crack, its more like 2 pieces of paper that are pushed together and the edges push upward where the 2 papers meet, ...kind of like plate tectonics on a nano scale.



Anyone have any idea what is going on. it is the only flaw in the entire job. Believe me when I say there was no contamination.

jmd_forest

[jm529]

jmd, that is not contamination. it's lifting the base or primer up again. what materials are you using? are they compatible? it might just be that its too cold for you to spray and you have to let every coat flash longer.

[jmd_forest]

The bumper was brand new, It was wet sanded, cleaned, Bulldoged, 2k primered and the primer crazed like crazy. Stripped with Bulldog stripper, wet sanded, cleaned, Bulldogged again, and primered again. This second attempt at primer came out perfect, but it was applied in cold weather (about 50 degrees). This second coat was wet sanded and allowed to dry overnight.

Yesterday, it was 60 degrees here. Applied 2 coats of base, allowed long flash times (25 minutes) and all was OK. Applied first coat of pearl and between first pearl coat and second pearl coat you can see what happened.

The base and pearl are PPG, the 2K primer was Finish Pro (sold with the PPG by local paint shop) the Bulldog adhesion priomoter was.......Bulldog.

That 1 spot was the only real flaw in the 4 panels shot yesterday (tiny run in the clear on 1 fender but that will sand out).

Any recommendations on repair techniques. My plan is to carefully sand smooth, fill with acrylic glaze if necessary, and spot repair using light coats blended into the surrounding . I'm afraid if I recoat the whole thing I'm just asking for more trouble.

jmd_forest

[jm529]

if that is a 3 stage paint, you might be better off starting from scratch. it'll be real hard to blend and get the pearl to look right and to get a good match. if you're shooting in 60 degree weather are you using the fast reducer? if you're using mid temp, you better heat up your spray area more. i still think that everthing is staying too wet or being sprayed too wet.

[jmd_forest]

Yes, I'm using fast reducer, PPG DT860 (60 - 70 degrees). I could be spraying too wet, I am only an amatuer. I did let if flash a good long time, 25 minutes - 30 minutes between coats.

I do understand the problems blending the pearl, but I'm going to give it a try. I have enough paint left over to redo the cover if necessary

Thanks for the replies.

jmd_forest

[BReyes]

Definitely too wet. Hope it warms up soon ( I can't imagine painting with such low temps. i am from Florida. All that will be behind you soon. Hey forget this quiting part, you can't quit. Next thing I know you will be doing a 911, right?

[jmd_forest]

Did a 68 911 Targa many years ago. Took 2 tries but it did come out quite nice in the end.

Can I just gently sand this out and spot repair, or maybe reshoot the cover or will this require serious sanding down to the plastic and an entire reshoot?

Thanks for all the help.

jmd_forest

[BReyes]

Most people don't match the bumper cover exactly as they use flex additive. Don't hold me to that. I am just saying, yeah , start over. sand prime sand paint etc. I think you wrote your spraying is matching in the other areas.