Underbody and suspension coating: SO many options!?

[Josue]

I'm hoping I can get some help in choosing the right product to use on our '69 Firebird convertible project, there seems to be ALOT of choices!

It's your typical restoration project though, we're looking to paint the subframe, suspension parts, underbody, floor boards inside the car, axle, leafs, etc. So far, I've researched...

POR 15- Seemed like the front runner because of how well it looks on paper, and alot of people swear by it, but I've been reading about more and more problems with it not sticking to bare, sandblasted metal?

Chassis Saver- cheaper POR 15 knock off that I read some good reviews on, but also the same lack of bare metal adhesion problems as well.

PPG DP90- A PT and restoration shop we visited said they used this on all their projects, but something about leaving primer on a car doesn't quite sit right with me for some reason? I'm a body man, so all my years in the business have me used to seeing a car being primed, then immediatly painted. lol Can you really just leave bare primer on the underside of a car like that? Will it really last for years and years and years? Or am I misinterpreting this product's use of the term "primer" all together?

And I've read that all three of these need to be "top coated" in order to be UV protected, but.....none of the parts that will have these coatings will be exposed to direct sunlight, so how much of a problem is their lack of UV protection really going to be? Also, what do they mean by "top coat"? Do they just want you to base/clear over the coating? Or is there simply a "top coat" you have to buy and apply over the products?

And then there's a few random, "rust inhibitor" products that each person swears by, but that's what has me confused on what to go with, everyone's got a different opinion! This guy says he uses THIS product and swears by it....that guy says he uses THAT product because the 1st product didn't work for him, and he swears by it....the other guy says he uses THIS product because both other choices didn't work for him, but this one is perfect......you get the point. lol

And I know powdercoating is always an option, but you can't powdercoat the underbody of a car. haha And, PC'ing doesn't stop rust from forming, but if you PC blasted parts, will this really be an issue? And in the same fashion, I've found some negative opinions on PC'ing, stating that rust was forming underneath the powdercoat...so it seems like that option has it's con's too.

Help a newbie decipher all this conflicting info!!!

[Yoda4561]

PPG DP-90 is an epoxy primer, which is a different animal from the primer that goes on just before the basecoat. It's very durable, chip resistant, and chemical resistant once it cures. Epoxy is the (best)first thing that goes on the bare steel, after which there's a "normal" primer, base, clear. As a chassis paint it doesn't need to be topcoated, since it won't be exposed to enough UV to be a problem. If you're worried about it any of the "chassis black" paints can be applied over it.

Almost every time rust forms under a powdercoat or epoxy it's due to poor surface prep. Products that contain acid, like those "rust inhibitor" products you were talking about almost always leave some residue that if not 100% removed will eventually cause the coating to bubble and let rust form. Soda blasting can have a similar effect if not properly removed before painting.

[Josue]

PPG DP-90 is an epoxy primer, which is a different animal from the primer that goes on just before the basecoat. It's very durable, chip resistant, and chemical resistant once it cures. Epoxy is the (best)first thing that goes on the bare steel, after which there's a "normal" primer, base, clear. As a chassis paint it doesn't need to be topcoated, since it won't be exposed to enough UV to be a problem. If you're worried about it any of the "chassis black" paints can be applied over it.

That's kind of what I was thinking the case was, since I had never heard of DP90. I wouldn't be worried about the lack of UV protection though, since like you said, the DP90'ed parts won't be exposed to UV rays. lol I was just a little skeptical.


Almost every time rust forms under a powdercoat or epoxy it's due to poor surface prep. Products that contain acid, like those "rust inhibitor" products you were talking about almost always leave some residue that if not 100% removed will eventually cause the coating to bubble and let rust form. Soda blasting can have a similar effect if not properly removed before painting.

So, we'd pretty much have to just trust the powdercoater's prep then in that case? Or make sure WE do it right if we tried to a DIY method...

[61ragtop]

I used a product called Endura. I believe it is even used on aircrafts. It is very durable and can be matched to any color.

[Josue]

How did you hear about that product? And what made you choose that over the above methods?

[61ragtop]

It was brought up by my painter. I picked it because I wanted to color match the floor boards to the body and I was told it was very durable too. I used a combo of single stage gloss black paint and powder coat for the chassis.

[Josue]

Cool. Thanks for the info!

[HOTRODSHOP]

With the DP epoxy it comes in several colors including black,,,its what i use on everything before any work begins as soon as its in bare metal,,its also best to do your bodywork over it also. you wont go wrong using it .

[Josue]

So, what kind of process should I go through with DP90?

I wanted to have the body blasted before I started welding parts on it, just so we could uncover any hidden problem areas that would need attention as well. Would it be best to do this, then spray DP90 over EVERYTHING, then grind it off whatever areas I'd need to weld to?

Or, a friend of mine suggested to go ahead and weld all the parts on, then have it blasted, so they can clean my welds up. And I found a blast shop that will blast AND spray everything in DP90 for 1 price. Then he said I could do my body work right over top of it from there...

[HOTRODSHOP]

yep,,i would grind and weld my parts and then blast and prime with DP90

[armourmark]

I also use DP90 on my chassis. The catch with UV is that it doesn't have to be in direct sunlight to be affected by UV. You can spray the DP90 and then clear coat it for protection.

[Josue]

yep,,i would grind and weld my parts and then blast and prime with DP90

What would happen if after I welded the parts on, grinded the welds, blast and primed, and then found some additional holes here and there that needed patched? Can you spot DP90 in? Or will the whole underbody need resprayed to get a uniform coat back?


I also use DP90 on my chassis. The catch with UV is that it doesn't have to be in direct sunlight to be affected by UV. You can spray the DP90 and then clear coat it for protection.

You can just clear right over DP90? The clear will be enough for protection?

[HOTRODSHOP]

Just spot it and yes you can clear it also

[Josue]

Well that sounds simple enough! I think we might go with that for the underbody and interior floorboards, but I still need to decide on the suspension parts and subframe. I don't know if the 'rents will have enough money for powdercoat, which would be my 1st choice. I still might look into prices though, just so they know the option is there.

Really appreciate all the help guys, I can't stand being confused. lol

[mc84_zz4]

I would recommend checking out Eastwoods products www.eastwood.com
Their chasis black applies in a nice coat(s), you can recoat again with same finish, and if needed use their 'rust encapsulator' as a primer on areas that may have had rust, and they will stay painted.
I sprayed my driveshaft before hammering out the u-joints, and was impressed by the beating they took. BTW my propane torch did not even phase the paint.
It takes literally a day to completely dry (my experience in high humidity), but it gives great results, they also offer various levels of gloss. Also, their latest chasis black is also resistant to brake fluid. I would highly recommend.

[Josue]

Would we need the rust encapsulator if we were applying the chassis black over bare metal?

[mc84_zz4]

Would we need the rust encapsulator if we were applying the chassis black over bare metal?
Nope, just scuff anything with a red scotch pad (200 grit) and spray. I followed up the scuffing with a paint prep wipedown. Their spray cans spray beautifully BTW, and is very forgiving, I have not made a drip or rough spot yet.
The rust encapsulator is a flat black, the chassis black is a 70% gloss (slightly slicker than satin). Good durability, hammers, srapes, etc.
And it does look that black...
https://static1.pt-content.com/images/pt/2009/10/03_Frame_Cleanup_Painted1-1.jpg
more pics: http://www.motortopia.com/album/view/p/cars/t/vehicle/v/11982/a/13805/i/engineswap_ch1

[Josue]

And they sure do have alot of products to confuse a customer!?

-Full chassis restoration kits
-Extreme chassis restoration kits
-Original chassis black
-Extreme chassis black
-2K ceramic chassis black
-rust convertors
-rust encapsulators
-primers
-activators
-anti-rust something

Man oh man!

[Josue]

Nope, just scuff anything with a red scotch pad (200 grit) and spray. I followed up the scuffing with a paint prep wipedown. Their spray cans spray beautifully BTW.
The rust encapsulator is a flat black, the chassis black is a 80% gloss (slightly slicker than satin). Good durability, hammers, srapes, etc.

That's good to hear. I do alot of spray can painting (VHT Niteshade tail light tint, and Autozone clear coat) and almost half the cans I get have messed up tips and don't spray right. Money is going to factor in greatly with them at this point as well, so they may want a cheaper solution for the subframe and parts.

I wouldn't need to scuff sandblasted parts though right? You were just referring to regular metal?

[mc84_zz4]

That's good to hear. I do alot of spray can painting (VHT Niteshade tail light tint, and Autozone clear coat) and almost half the cans I get have messed up tips and don't spray right. Money is going to factor in greatly with them at this point as well, so they may want a cheaper solution for the subframe and parts.

I wouldn't need to scuff sandblasted parts though right? You were just referring to regular metal?

I have only applied it on raw or sanded metal parts, not sure if your media/sand blasting leaves a coating on the metal, as long as the surface has some 'bite' just wipe it down with a paint prep/degreaser and spray away.
All the surfaces I have sprayed get wire brushed (w/drill & brush), degrease, scuff, final degrease, then chasis black.
(the only reason I degrease 2x; it makes the scuff pads last longer and not contaminate other areas)

Slightly surface rust areas I treated the same, wire brush, then the first coat or 2 with rust encapsulator.
They have many other products, but for now those 2 are my main weapon. I have some others of theirs (rubberized undercoating, high gloss chasis black) but have not sprayed them yet.
If you have real rust and cannot replace, their rust converter will stop it (they advertise) similar to the POR-15 advertising...

[Josue]

Alright, so kind of what yoda was saying up there about after blasting. I just need to make sure the surface is cleaned well and I should be fine...

[BRIAN]

POR 15 Is highly over rated. It works great on metal with flash rust. Great to seal back of panels or seams that you are not going to blast.

If you are looking for a cheap solution that can easily be applied at home try Rustoleum quart of satin black 777 or 7777 that can be sprayed easily. Rustoleum also sell a small container of a rust seal that converts rust to a black paintable coating. It works great and is just as good as the more expensive stuff.

Spray can resto??? Krylon satin black can't be beat. Nice thin coat that lasts and can be spot repaired.

Remember if it is a driver it will need touch up work so stay away from any gloss paints.

Most PPG base or interior flats can have a hardener added and will be UV stable and tough as nails.

[Josue]

That's funny you should mention!

I'm doing the body and paint work for my neighbor's 73 Ford Truck. It's completly torn down as well, and he just got the frame all put back together, but he used Rustoleum gloss black, and silver on some suspension parts. Doesn't look bad!

[Yoda4561]

Yeah, plain ole rustoleum or krylon can be fairly durable if surface prep and good coating habits are used. I painted our house's steel door handle 10 years ago with some krylon primer and black gloss paint. A couple hurricanes, 10 years of sun, and countless thunderstorms and while it's dulled a bit there's no paint lifting or rust underneath the paint.

[Josue]

Hmm.....VERY interesting!

Here are some shots of his Rustoleum job...

https://static1.pt-content.com/images/pt/2009/10/104_40411-1.jpg
https://static1.pt-content.com/images/pt/2009/10/104_40451-1.jpg
https://static1.pt-content.com/images/pt/2009/10/104_40421-1.jpg

[68400BIRD]

So far I have used DP90 on all of my floor boards and firewall. After spraying you have up to one week to top coat without having to scuff the surface down. If you go with the DP90 you can buy it where you have two different pot lifes. One is eight hours and one is 72 hours. The only down fall is the 72 hour option has an induction period of a half hour.
I use POR15 on all spots that have been sand blasted or have had some rust. The key to por15 is again in the prep. It sticks great to seasoned metal, very well to metal that has been prepped with acid and horrible to anything that has paint on it.
To top coat the por15 I wait untill it is tacky to the finger(no paint on finger) and then spray two light dustings on it. Once fully dry I spray my top coat on it. It turns out very durable. Better than anything out of a spray can in my opinion. I plan on painting the lower side of my car in gloss besause it will be driven a lot when done. I figure gloss is a lot easier to clean up that a satin is.

[Taman]

I too have used POR-15. The first time the POR peeled off after a couple of years. The second time I bought all the Products they recomended. That even peeled. The only part that doesn't peel is my battery tray that was rusty from the battery over the years. Wore like iron and never peeled. The rougher the surface the better it stays.

[forcefedturbine]

I too have used POR-15. The first time the POR peeled off after a couple of years. The second time I bought all the Products they recomended. That even peeled. The only part that doesn't peel is my battery tray that was rusty from the battery over the years. Wore like iron and never peeled. The rougher the surface the better it stays.
^^ X2 yea bare metal por15 isnt the best deep pourous rust like an and old rusty frame it does great

[Josue]

Bumping this up to get some new opinions!

I'm close to welding the floor in on the Firebird, and I need a product to put on the insides of the rear frame rails, convertible brace (under car) and the front floor braces as well. They're rusty, but still solid, so we just want to put something over the rust to stop it.

[rohrt]

When I worked on my bird I used POR in areas that would not be seen that had rust like the inside of the doors and under the dash. Areas that would be seen I had sand blasted (like the whole shell) and use sherwin self etching primer then the DP90. Its pretty amazing how well my underside of my car has held up. I think the self etching two part primer before the DP90 was a good step for me.

I only had one floor patch. I ground down the welds and used a seam sealer on the bottom side and smoother it on. The floor seam blends in very well and hard to detect.

[64impala]

What I did on my 64 underside and frame was i used KBS Rust Seal. On the floor, after the KBS coating was curred, I scuffed it and applied Monstaliner Undercoating. Amazing product. Inside the frame rails i sprayed Eastwood Internal Frame Coating.