Undercoating that neutralizes rust

[67Customs]

If all the rust is actually removed, then yes, normal paint will be fine. However, if aren't going to remove all of the rust before you paint, then POR-15 will work better than regular paint. POR-15 requires that you remove the loose rust before you paint. Not all of the rust from the surface before you paint.

When I said with proper prep, I meant proper prep for adding POR-15. Not proper prep for any old paint work.

Rugular paint will flake off and bubble up over the rust. POR-15 wont. If regular paint would suffice, then you wouldn't need to add multiple coats...

I started painting under mine when it had less than 500 miles on it. Has maybe 100 coats added by now

I painted the bottom of a '67 Mustang (notorious for floor pans rusting) during restoration as well as other parts with POR-15 six years ago and it hasn't needed a touch-up yet. I simply knocked off the loose rust and applied the POR-15.

 

[zoomie]

Are you thinking of Naval Jelly? That's supposed to stop rust.

 

[tjkj2002]

POR-15 is far from junk/snake oil. I've used it/seen it used on multiple occasions and it works very well. If the surface is preped properly, it does an excellent job of suppressing the rust and I've never seen it flake off.

If you don't feel POR-15 is adequate to solve the PO's problem, why don't you offer a suggestion of something that can?

It flakes off,seen it many times.Never seen it not flake off after a few months.

Use a wire wheel to get as much as the rust off and use Epoxy Primer,will stop the rust longer the POR-15 will.


The only way to 100% stop the rust is to cut out all the rust and replace with new sheet metal and properly prep/paint it.

 

[67Customs]

Never seen it not flake off after a few months.

Come out to NC and I'll show you a couple of jobs that it hasn't flaked off.

I don't want to turn this into a "which product is better/who is right" argument. I'm just here to tell you that POR-15 has worked for me and has worked for people I know and that I'm throwing it out there as an option.

 

[TAHOE]

I've used a product called Rasonil/picklex20, it is a rust convertor that once dried, it can be painted over. Worked pretty well.
Agreed, the best way is to completely remove rust but chemical means or maybe some type of blasting, but if not possible then there is other alternatives. I do not like POR15 just due to the hazard of using it. There is also Eastwood products, Zerorust, etc.
I've found one of the easiest/cheapest solutions is a to clean as much rust from surface as possible even if that's just a good wire brush and wipe down with acetone. Then I coat with a thick layer of Rustoleum Heavy metal primer( can be 10-15% thinned and sprayed or buy already in spray can), then top coat with Rustoleum paint. For $7-8 quart @ wally world, it kicks some good butt!!!! Example- I lightly sanded a utility trailer that was pretty rust in 1993, clean with acetone then put a heavy layer of the primer on it, never top coated. It was only 2-3 years ago that rust started appearing again... that's 15yrs with only the primer. Pretty good protection for what it is.
Like stated above... surface prep and cleanliness is key for any surface treatment...and 10 different people wil give you 10 different opinions on what's the best.