Repainting Infiniti Bumper Covers

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PostPosted: Tue Oct 01, 2019 3:04 pm
I recently repainted both bumper covers on my Obsidian Black 08 Infiniti G37 Coupe. The rear was a respray and the front was an oem Sport bumper that I replaced my Base model with. I used primer, urethane base coat, and acrylic lacquer from Automotive Touch Up. The finish came out looking very nice until a day or two after I'd put the finished covers back on the car. I started finding cracks and spider webbing around the sections on the covers that had been bent and stressed while putting them back on the car. I was told by them when I bought the paint that I wouldn't need to add flex to the primer or the clear that it was fine as is. I called Automotive Touch Up and, to their credit, they've replaced and/or upgraded the primer, basecoat, and clear that I bought for the job. They upgraded the primer to 2k and the clear to Acme Finish 1 2k. The base coat is the same 1k urethane that I've already used. They told me again that I wouldn't need to add any flex to the 2k primer or the 2k clear but I'm not sure I'm buying this judging from what happened last time. Should I add flex or take their word that it doesn't need it? I'm assuming that I'll have to sand everything off both covers and start with a bare surface or do I just need to sand off the clearcoat? I really don't want to have them cracking again. Any advice, opinions, and help will be greatly appreciated.
Regards, Sam

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PostPosted: Tue Oct 01, 2019 9:59 pm
Hey, Sam.....yeah, the lacquer acrylic clear bit you on this one. Yeah, I'd be sanding all that off. Now, you are set up with an all 2k system it sounds like so you should be good. Most (not all) modern urethane based paints are flexible enough themselves without needing additional flex additives. I don't think I've used one since 1992 or so. Might want to let the bumpers set for a few days to a week so everything is crosslinked well before mounting. And of course go slow on the mounting......
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PostPosted: Tue Oct 01, 2019 11:33 pm
Thanks for getting back to me. Yeah, it bit me pretty good, LOL. It just makes me sick to have to sand it all off. It really looks good except for the cracking spots. I do know that it'll start cracking everywhere pretty soon. Should I sand everything off or just the clearcoat? I'm thinking I should sand it back down to the bare plastic and do it over. Should I use around 26 psi at the gun for shooting the primer and clear? I'm a rookie and haven't used 2k paint before.
Thanks, Sam
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PostPosted: Wed Oct 02, 2019 11:30 am
Dont' take a chance.....get it all off. As for your gun settings. What do you have (brand, model, tip size, etc.) and what's your compressor situation like.....
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PostPosted: Wed Oct 02, 2019 12:10 pm
id be concerned about what type of primers on there.ive only done 5 or so bumper cover resprays and went with what my sons step dad- whos been painting since the model t- said:
if its a urethane bumper, which most are, and urethanes are used for primer,base,and clear, youll be good.
i still see the honda crv i did 3 years ago with matrix urethanes and its still in great shape. no cracking or adhesion problems. its a metro detroit daily driver,too.



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PostPosted: Wed Oct 02, 2019 2:57 pm
Compressor is a Harbor Freight Central Pneumatic 21 gallon, 2.5 hp, 5.8cfm @ 40 psi and 4.7 cfm @ 90 psi with an inline moisture trap and regulator about 5' from the compressor. My gun is an Eastwood Concours LT100 HVLP that requires 4.5 cfm at 30 psi. I've got 1.3mm, 1.5mm, and 1.7mm tips, a Fisheye moisture filter and air regulator on the gun. I already had the compressor so I bought a gun that would work with it. I'm retired and on a fixed income so I'm not going to be spending a lot of cash on a new compressor. The gun and compressor work well together, it seldom kicks in while I'm spraying at 26 psi indicated at the gun. I'm not going to be painting whole cars with it, just parts. I'm painting in my attached garage with everything covered up with plastic drop cloths and two 20" fans for ventilation. I do get a little trash in the finish but nothing that I can't wetsand and buff out. I bought the G37 when I retired two years ago to have something to do. It was a relatively cheap, at $6k, and unloved car but mechanically sound with 78k miles on the clock . The paint is/was not the best, both bumpers were dented and cracked, interior is not bad at all. I bought a used rear cover in good shape and a slightly repaired front Sport cover (it had had a 1/2" hole in it that had been nicely repaired) to replace the Base cover it came with. I've also got a complete set of Sport skirts/rockers that I found in a local salvage yard cheap that I've still got to paint. The hood has small dull dots on the paint that look like chemical burns to me. It looks like it's had droplets of carburetor cleaner get on it and its burned the clear. Haven't tried wet sanding that yet as I think the spots have probably eaten through the clear.

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PostPosted: Wed Oct 02, 2019 10:56 pm
Well, if you're just doing parts and it's working keep at it. Just use whatever pressure is getting you a decent pattern with the coats flowing out properly. Does sound like that spot damaged stuff is pretty cooked....I'd be going down to metal on those surfaces....
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PostPosted: Fri Oct 04, 2019 5:11 pm
Would wet sanding the bumper covers with 400 be gritty enough to strip it clean and leave a smooth surface for the primer?



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PostPosted: Wed Apr 15, 2020 6:01 am
I'm pretty much on the same boat as you, same color and everything. I have to resand and repaint. What grit did you use to get all the paint off. ?

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