[ZeGermanHam]

Hi all,

I replaced the full trunk pan and floor pan under the rear seats in my '66 GTO with panels from Ames. I'm now getting ready to prime the underside of the body and apply undercoating.

Do you guys think it's necessary to strip the e-coating off before priming in this area? Maybe just scuff it good with 80 or 120 grit? Again, this is just for the underside of the body - nowhere that will be body color painted.

Thanks in advance.

[Flynbye]

Solvent test the e-coat to see if it is soluble. Rub it with lacquer thinner on a rag. If it comes off, take it all off. If it doesn’t, leave as much as possible on and just scuff with a red scotchbrite and continue.

[Greg Reid]

Boy, that would be a real PITA if you had to strip all the coating off the underside of a trunk pan, braces and all.

[ZeGermanHam]

Yeah, I'm hoping a scuff job will suffice, but I'd like to get input from as many people here just to be sure.

[Greg Reid]

Flynbye's suggestion above is the general rule that I've heard before.

[MUSLCAH]

I would scuff with maroon scuff pad...2 coats of black epoxy ..and call it good. I hate undercoating...it looks like your trying to hide something. Plus when I check undah my Cah to inspect things ....I like to see what’s going on......with a coat of undah coating your screwed.

[ZeGermanHam]

Yeah, I've put this question out there in a few other places and so far everyone is saying to leave it on and scuff. Seems fairly unanimous at this point. Lord knows I certainly don't want to go through the extreme hassle of removing it if it's not absolutely necessary.

[Flynbye]

Have you tried a solvent test? If it stays on, it’s easy. If not, you have to decide if the extreme hassle Is worth it.
There is a lot of chatter in the collision repair business over this very topic. I’ve been in deep conversations with representatives of the largest collision repair organization in the country over it. Some think the primer on new parts, whether OEM or aftermarket, is just a “shipping” Primer.
The fact is, that every paint manufacturer worth their salt, will tell you the same thing I did.
If you decide to continue the paint process over a soluble substraight, no one will warranty their product!
I will qualify this with you talking about the underside. It is not nearly as important as the exterior, specifically the top surfaces. I will go further saying that depending on the refinish product you are using, you may not have to scuff the e-coat at all!
The balls in your court.

[ZeGermanHam]

Originally Posted by Flynbye

Have you tried a solvent test? If it stays on, it’s easy. If not, you have to decide if the extreme hassle Is worth it.
There is a lot of chatter in the collision repair business over this very topic. I’ve been in deep conversations with representatives of the largest collision repair organization in the country over it. Some think the primer on new parts, whether OEM or aftermarket, is just a “shipping” Primer.
The fact is, that every paint manufacturer worth their salt, will tell you the same thing I did.
If you decide to continue the paint process over a soluble substraight, no one will warranty their product!
I will qualify this with you talking about the underside. It is not nearly as important as the exterior, specifically the top surfaces. I will go further saying that depending on the refinish product you are using, you may not have to scuff the e-coat at all!
The balls in your court.

I keep the car in a shop space a few miles away from home, and I haven't had the chance yet to try the solvent test. I'm pretty sure it won't come off with solvent, but I will test tomorrow morning. The e-coat on the parts seems really nice to the touch, so it seems like it would be pretty silly to apply such a nice finish just for shipping if that was the manufacturers intent.

[MUSLCAH]

The only primer I have seen in my 44 years of this stuff....that wipes off with solvent .....is a waterborne primer used on the aftermarket bumper covers. I use a waterborne cleaner on them. But as far as E coat on Metal washing off.....I Ain’t seen that.

[Flynbye]

You need to know that primer on plastic bumper covers is not e-coat. Bumper covers have always been suspect. Especially aftermarket (Keystone).
You’ve been around 44 years, you remember when Ford recommended in the 90’s complete removal of their e-coat before painting? I do. Pain in the ass.
I have seen many times factory OEM replacement parts with soluble e-coat. It happens. Usually underbaked.
E-coat is probably the best primer to have as a base. Just needs to be insoluble.

[1965gp]

On my K5 the fender wells came with that e-coat and I did as suggested- red scotchbrite and good under hood paint.

I would not use 120 and definitely not 80 grit. I thi you will see the scratches in the final coat.

[Jerry H.]

Red scotchbrite and DP90 epoxy primer.

[400 4spd.]

I'm not the fan of Scotchbrite but prefer 320 grit (dry) for epoxy or paint prep. We do as Muslcah does, sand and apply two coats of epoxy primer. DP90 would be my choice.

[ZeGermanHam]

Thanks for all the input, guys. I truly appreciate it.

Since I'm a complete newb when it comes to automotive painting of any sort, how many quarts of DP90 do you guys think I'll need for two coats on the full underside of the body and wheel wells? I'm getting ready to buy supplies and this is all new to me.

[400 4spd.]

I would expect about 3 quarts. You might buy a gallon for a small amount above the three qts. You'll need the activator (401 or 402) and a small amount (10 percent) of acetone for reduction. I suggest 402 as more user friendly, as 401 requires an induction period after mixing.

[MUSLCAH]

Originally Posted by Flynbye

You need to know that primer on plastic bumper covers is not e-coat. Bumper covers have always been suspect. Especially aftermarket (Keystone).
You’ve been around 44 years, you remember when Ford recommended in the 90’s complete removal of their e-coat before painting? I do. Pain in the ass.
I have seen many times factory OEM replacement parts with soluble e-coat. It happens. Usually underbaked.
E-coat is probably the best primer to have as a base. Just needs to be insoluble.

Yup...I felt bad for my buddies at the Ford Garage...one aftah another...for a long time.

[ZeGermanHam]

If I decided not to use a flexible undercoating as a topcoat over the PPG DP90, is there another product that you guys would recommend? Does the DP90 need a topcoat?

[400 4spd.]

Different opinions on that question, but I always top coat DP. DP doesn't have UV inhibitors, so it "breaks down" when exposed to sunlight. Of course it won't see direct sunlight under a car, but for durability I always top coat with a single stage product with some flattener added.
In fact before a floor pan is installed the underside gets sanded and sprayed with DP90.

[nytrainer]

Originally Posted by 400 4spd.

Different opinions on that question, but I always top coat DP. DP doesn't have UV inhibitors, so it "breaks down" when exposed to sunlight. Of course it won't see direct sunlight under a car, but for durability I always top coat with a single stage product with some flattener added.
In fact before a floor pan is installed the underside gets sanded and sprayed with DP90.

That’s one reason I always lean towards SPI black epoxy as I understand it has UV inhibitors. Plus I like the way it looks (sheen), sands and costs.
I thought you (400 4 spd) were an SPI user?