should I POR15 or Rust Bullet underbody?

[kielbasa]

Hi guys, I have rear axle, leafs, trans removed from cuda and would like to repaint underbody as well.
However, I'd like to first coat the underside with por15 or rust bullet (or anything else you would recommend), and then finish with the original color (yellow).
Sounds like the por15 needs a lot more prep (acid wash, etc.) vs Rust Bullet......kinda hard to do while laying underneath a car.
Any of you guys went this route and could offer suggestions? Thanks!

[ChallengerHK]

My thought is that POR-15 is not suitable for doing the entire underbody. It's going to be very expensive, and even with the acid wash prep I don't think the stuff is sufficiently resilient.

My plan is to go with Rhino lining.

[burdar]

If you are going for a factory look, don't paint the underside yellow. Cars weren't painted body color from the factory on the underside.  The correct factory look is gray primer with yellow overspray.  You can use an accual paint that is the same color as primer for more durability.

I would not use POR 15.  I've never used Rust bullitt.   

[LAA66]

 Ive never tried POR 15 but have used Rust Bullet. Stout material for sure, quite toxic though. Be careful.

[GranCuda1970]

Yes, becareful if you use the POR-15 , I had my little brother shoot the POR on the underside and the uncovered parts of his face and arms were black for 3 days he had to scrubb off several layers of skin I had a hard time not laughin my arse off.

[dutch]

dont know about rust bullet but por15 sucks. If you have a tiny place with bad adhesion ( which isnt uncommon with this stuff...) , the rest will peel off with it like it`s one big plastic bag.

[Topcat]

I've used Rust Bullet before and really liked it. I hear it's easier to sand to prepare painting over it than POR-15.

[tommyg29]

I used and liked the eastwoods products. They have lots of underbody products. I used the rust converter and rust encapsulator and the chassis black. Check them out.
Not a lot of prep needed other than descaling and normal cleaning. Did it about 18 months ago and it still looks good.

ps- I also recommend getting one of those flex tube attachments for spraying inside frame rails and other openings, etc.

Before and after:

[larry4406]

If you are going for a factory look, don't paint the underside yellow. Cars weren't painted body color from the factory on the underside.  The correct factory look is gray primer with yellow overspray.

My 71 barracuda vert has the original metallic bronze paint under the floor plans, up into the transmission tunnel, the rear floor boards, the rear wheel wheels, etc.  If it was over spray, they did a great job. Can't tell about the under trunk area as the trunk has been replaced already and I don't have any pictures of what it looked like before.

[GranCuda1970]

Well I hope the POR-15 lasts We scrubbed her down to the metal and wiped her clean several times with Solvent and then isopropyl alcohol on cheesecloths before applying the layers , primer and the PPG paint underneath her is as hard as a rock now, even the paint drips feel like steel. I do not plan on EVER driving in the rain but I always got caught in it when drivin her before.

[burdar]

My 71 barracuda vert has the original metallic bronze paint under the floor plans, up into the transmission tunnel, the rear floor boards, the rear wheel wheels, etc.  If it was over spray, they did a great job. Can't tell about the under trunk area as the trunk has been replaced already and I don't have any pictures of what it looked like before.

You have to remember that back in the 70's it was people who sprayed the paint...not robots.  Every car is going to have a unique spray pattern on the bottom.  If the painter felt good that day or had to get rid of some extra paint, he may have gotten decent coverage on the bottom.  If he was hung over, he may not have bend down to paint the underside very much.  The cars weren't up in the air when they were painted.  The workers had to bend down to paint the rockers. 

Here is a before shot of an OE gold Challenger for reference.  You can see that the gray primer is still visable as well as the white overspray.
http://board.moparts.org/ubbthreads/upload2/4502609-CopyofChallengerJune200616.jpg

Here is the car after paint.  This is a typical factory style paint job.  Some cars may have more paint on the underside....some cars may have less.  Every car is different.
http://board.moparts.org/ubbthreads/upload2/4502626-Copyof100_2512.JPG

[kielbasa]

I actually spent several hours cleaning the underside of the car with hot water and a toothbrush - what I found was a clean rustfree with the original gray primer in very good condition. I decided to keep it original, so I after cleaning it. I coated the cleaned area with LPS3.
The car was from South Carolina and the entire underbody is coated with red clay - seems to be a heck of a corrosion preventor.
Because the car had a schlup repaint sometime in the 70's, there was overspray in the wheelwells - I found that 1 coat (2 coats gets glossy) of semi gloss POR15 over the factory undercoating turns out great.
I will begin working towards the front of the car removing the red clay (time consuming grunt work)!