Paint and Body Undercoat or not? If not, then what?

7991LXnSHO · Sep 26, 2021

I have a car in the shop where I am using my checkbook to get the bodywork done.
It is a low mile and very low rust car. As it is a budget restomod that’s I am going to drive, I am not going “frame off” (on a unibody-we need a better term).
The top side looks great now. And I had planned on them spraying por-15 on the bottom side of the car. The shop no longer wants to do use POR-15. Apparently, they do not like how hard it was to clean up after with a bunch of other not do legit excuses . But they will use a good brand of rattle can undercoating.
I am worried about undercoating making things worse over 1960’s original finish floors and in fenders without a good surface sealing first.
What should I do? I need some pro’s to verify or update my old knowledge.
Thanks!
@horse sence @Davedacarpainter

horse sence · Sep 26, 2021

I actually prefer epoxy primer ,red oxide . The primer i was using is no longer available here but i would like to try SPI primer ,it looks about the same . I was using colar and when sprayed over a blasted surface you will never get it off . I never liked por15 ,i have seen it peel off in sheets if not applied correctly .

horse sence · Sep 26, 2021

Absolutely do not use rattle can

7991LXnSHO · Sep 26, 2021

So far I am up to date. Putting tar all over everything seems like a dealer mark up bad idea. And it is not getting blasted on a rotisserie this time. :-(

I was thinking about the consumer product Rustoleum Rusty Metal primer. But the pic on their site is for clean metal primer.

https://www.rustoleum.com/product-catalog/consumer-brands/professional/rusty-metal-primer/

Davedacarpainter · Sep 26, 2021

No rattle can undercoating, nope, nope, nope.

I like POR15. It’s a great product if applied properly. Clean up problem? Um, I guess so. No more than anything else though.

Epoxy primer would probably a better initial coating for you. It’ll adhere to the bare metal spots without an etch primer.

The fact they’re saying they want to use the undercoating is a bit surprising to me.

7991LXnSHO · Sep 26, 2021

Thanks.
In the 80’s, there were coat, convert and encapsulate all in one products. One went on like watered down Elmers School Glue, and turned black on the rusty floorboards, ready for primer and a top coat. Is there something like it but better now?

horse sence · Sep 26, 2021

7991LXnSHO said:
Thanks.
In the 80’s, there were coat, convert and encapsulate all in one products. One went on like watered down Elmers School Glue, and turned black on the rusty floorboards, ready for primer and a top coat. Is there something like it but better now?

That used to soak into the seems and overlap joints ,when it would rain or just get wet it would start to rust again ,i used to turn down paint jobs when they brought one to me with this . The best thing to do is remove the rust and a good coat of DTM or Epoxy . Seal all seams with seam sealer.

wicked93gs · Oct 2, 2021

I just went with epoxy primer as the base followed by acrylic enamel for the engine bay, undercarriage, and interior non-visible locations. Its difficult to even scratch it with that combo. I expect it will hold up many years without issue...but I also don't plan on driving in the rain or salt so I did not feel the need for undercoating. Definitely do NOT use rattle can paint anywhere you want tough paint, its non-catalised and so therefore will scratch and get damaged easily.

horse sence · Oct 2, 2021

I have tried to blast away the epoxy primer and if it was applied over a blasted surface it is very hard to remove . I did spray bed liner in my 69 inside floor but it is catalyzed and i bet that will be a night mare to remove ,but it sure looked good

horse sence · Oct 2, 2021

manicmechanic007 · Oct 3, 2021

Ford sells the stuff in rattle cans
That said I would not use it except for touch up
Undercoat is sound deadener too
I like the Perma Plate stuff that is tar or asphalt based
The car needs to be steam cleaned underneath before application on a used car
I used to spray undercoat at the dealer and yes it is messy
Cleans up well with solvent
Used to keep some brand new solvent out of the safety cleen tank to use
Don't let them spray the gas tank, driveline or any suspension
Pay the dealer to do it then it will be done right and cleaned up well
Plan on leaving your car for at least 24 hours for the stuff to dry before you drive it
If you were around here I would do it for you for the cost of the stuff About 80

manicmechanic007 · Oct 3, 2021

manicmechanic007 · Oct 3, 2021

Above is the undercoat gun I use
It fits the cans you can buy from an auto body shop supply and is a 3M brand
Sprayed rocker shultz on the lower section of my Z28 years ago
Spray it yourself 7991LXnSHO
Great job horse sense

7991LXnSHO · Oct 3, 2021

manicmechanic007 said:
Above is the undercoat gun I use
It fits the cans you can buy from an auto body shop supply and is a 3M brand
Sprayed rocker shultz on the lower section of my Z28 years ago
Spray it yourself 7991LXnSHO
Great job horse sense

I am using the checkbook to do the bodywork this time. It’s about 20 rough years past when I can do this myself and get it done.

manicmechanic007 · Oct 4, 2021

7991LXnSHO,
Find someone like me in your area who will do a good job and not spray it all; over everything
Dealer used to be expensive because you would be buying a rust thru protection plan
If at the dealer tell the service writer guy you just want it sprayed
Buy your own stuff and then go down there with your checkbook
You should not get your balls broke then
The body shop supply should also have about 5 guys standing around sniffing paint that would be willing to spray it for you
Painting cars is a bitch Undercoat is easy The guy will be taking a break doing yours and so the fun scale goes up
Plus it's your bas arse hotrod The guy will get a kick out of doing it for you

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