929nitro

While working on the rear bumper for respray I noticed cracks in the original paint below both corners of the license plate opening. I started sanding on one and found the cracks are into the surface of the bumper material but are not evident from the back side. I sanded a small area down to the base material and can see the cracks but cannot feel them easily with my fingernail. What is the best way to handle these?

DUB

MAN do I HATE urethane bumpers.

I have seen this and also.

Sometimes it may be a staining effect that got into the urethane where there is actually no crack. Often times these stains look more like a light brown color...from what I have seen.

I have cleaned and prepped the raw urethane using PROPER CLEANING PRODUCTS (water based) and NEVER using a SOLVENT. Solvents on raw urethane can effect them and cause them to swell. And this INCLUDES 'normal' automotive wax and grease remover. There are special cleaners for urethane.

So doing it "the best way" as you wrote....the costs of doing this can become really expensive due to the amounts of products you may need for a 'one time' use...often causes people to use other products.

When I have come across spots like this and get them prepped....I shoot a special plastic primer and see if the cracks re-appear when it is applied due to being so thin. I am not writing that there can not be cracks there...but that type of urethane 'generally' does not crack unless it is really hit hard. And when this primer is wet..I try to flex the bumper to see if the crack increase in width when doing so.

I use NEXA products and their system of products for shooting on raw urethane and plastics. I can write that 'feathering back' these spots...and trying to do a spot repair on them can possibly cause you problems in the future where you might see a 'bulls-eye' effect in time when the products cure out and settle.

So not knowing how much you want to put into this or just doing a repair that will hold up for a while....You can call 1-800-647-6050 and respond to the teleprompter and get into TECH...and ask them if they can e-mail you the steps ( or guide you through the web site) and products needed for applying and prepping urethane. This is PPG's main tech center...and you can get the information for NEXA there also....just make sure you specify you want NEXA information...or PPG information...or both.

DUB

929nitro

Thanks for the input.

I am with you on the urethane bumpers.

I will give a call and talk with them. I want to do this right and make the fix as permanent as possible.

DUB

When I do bumpers like these...i take off all of the clear and basecoat. If I can...I try to keep the factory primer....which is why I HATE THEM due to the amount of time getting them prepped so there is no problems in the future.

I have had them baking soda blasted and had good results. But I also cleaned the bumper well over a dozen times....and it was raw urethane when I went to start applying my adhesion promoters/primers.

Just keep this in mind. If you do take to the point where it is raw yellow urethane....WHEN you get it cleaned....you want to be READY and shoot your first primer on it IMMEDIATELY. Don't wait...because raw urethane..when cleaned...its pours are READY for the primer....and if you let it set around...it is now being contaminated. AS you can tell...urethane bumpers make me MORE paranoid than I already am. Only because...a VERY LONG time ago.....I have had primer/paint/clear completely delaminate in a large sheet and fall off in time. Let that happen to you one time...and it will wake you up in a hurry.

DUB

929nitro

Thanks for all the warnings. I checked with my local paint supply house for Nexa and they said they carry Bulldog, I think it was by Kleen Strip. I am not worried about costs but if they do the same job with equal results and I can support my local supplier that is the way I try and go. If one product is superior to another than that is the way I want to go.

Dub you mentioned a special plastic primer, can you elaborate on this or is this the Nexa P572-2001?

DUB

YES...I believe so..because I am not at work right now so I can not say for certain 100%...but I am 99.999% sure that is the primer.

Also with NEXA's waterborne cleaner (P980-251).

YES...you can use the BULLDOG if you like because many guys along with myself do use it . But when it comes to raw urethane bumpers...I follow the NEXA process to the letter.

And that even goes as far as the primer I apply over the P572-2001. Which in many cases is NEXA's (P565-357) gray sealer WITH NEXA's flexible additive in it (P100-2020).

DUB

929nitro

Thanks for all the good advice.