POR-15 on undercarriage?

[Vincent72Q]

So it seems I'm in a pickle. I have been using a needle scaler to get the majority of the old factory rubberized undercoating off of my mustang (lots of work but came off pretty easily), there is still a residue in many areas but overall not too much rust underneath it and the coating was still in ok shape around the transmission area from oil/fluid leaks i assume. I still plan on going over the heavier rusted areas with a grinding wheel to clean up any flakey rust. I am wanting to use POR-15 on the entirety of the undercarriage but have some questions I am hoping you may be able to help me with.

A little backstory
The car has no engine or trans its pretty bare. I have removed all brake, fuel lines, and rear suspension so there is absolutely nothing on the undercarriage. I currently have the 9" rear end in the shop being looked at and tuned up so i have no rear axle, the car is in my workshop and I have no way of rolling it out.

Questions:
Por 15 works best on sound rust and bare metal surfaces as long as they are textured a little for the paint to grip. How well do you think it would grip onto old rubberized undercoating residue? Just incase i cant get some areas off.
How should i degrease the undercarriage? Its currently in my shop and I can't move it to hose it down after treating it with purple power.

Thanks for any advice in advance!

-The good son OP

 

[midlife]

I wouldn't put any paint designed for metal on any undercoating or seam sealer, as the rubberized stuff can flake off and take the paint with it.

 

[rvrtrash]

I would see if there is anyone in your area that could come out, mount your car on a rotisserie, wheel it out of the shop and either soda or dry ice blast the bottom to clean everything off. After that, spray the bottom with an epoxy primer to seal it, do any rust repair you need to and then spray the repair areas with the epoxy primer. You can have it tinted to replicate the red oxide from the factory if you want to get real fancy. After that, undercoat any areas that the factory did, or you want.

 

[Steve McMahan]

You could do what many of us have done. Use an angle grinder with a wire wheel on those areas of concern. I recently put POR-15 on the underbody of my 73 Vert and am very satisfied with the results. Some areas were mirror clean, and a few still had some of the original primer/paint from the factory. I did use acetone to clean off anything that might still be on the metal before I applied the POR-15. Not everyone on this forum thinks POR-15 is a good product. I’ve had good luck with it. Remember, once you put this stuff on, nothing else can be applied to it unless you follow specific instructions from POR-15. If you want more info, send me a PM.

 

[Stanglover]

I would see if there is anyone in your area that could come out, mount your car on a rotisserie, wheel it out of the shop and either soda or dry ice blast the bottom to clean everything off. After that, spray the bottom with an epoxy primer to seal it, do any rust repair you need to and then spray the repair areas with the epoxy primer. You can have it tinted to replicate the red oxide from the factory if you want to get real fancy. After that, undercoat any areas that the factory did, or you want.

Red Oxide? What red oxide.
I have a friend who also believes red oxide was used and put it on his 71 429 J code. Wrong, that was a Dearborn car.
Now, to be fair, I could be wrong if the car was from Metuchen, but I believe only up to 70 was red oxide used.

 

[Paul M]

So it seems I'm in a pickle. I have been using a needle scaler to get the majority of the old factory rubberized undercoating off of my mustang (lots of work but came off pretty easily), there is still a residue in many areas but overall not too much rust underneath it and the coating was still in ok shape around the transmission area from oil/fluid leaks i assume. I still plan on going over the heavier rusted areas with a grinding wheel to clean up any flakey rust. I am wanting to use POR-15 on the entirety of the undercarriage but have some questions I am hoping you may be able to help me with.

A little backstory
The car has no engine or trans its pretty bare. I have removed all brake, fuel lines, and rear suspension so there is absolutely nothing on the undercarriage. I currently have the 9" rear end in the shop being looked at and tuned up so i have no rear axle, the car is in my workshop and I have no way of rolling it out.

Questions:
Por 15 works best on sound rust and bare metal surfaces as long as they are textured a little for the paint to grip. How well do you think it would grip onto old rubberized undercoating residue? Just incase i cant get some areas off.
How should i degrease the undercarriage? Its currently in my shop and I can't move it to hose it down after treating it with purple power.

Thanks for any advice in advance!

-The good son OP

The important part is to not leave any rust. I used wire wheels, wire brushes, physically scraped the old coating off with putty knives, handheld sand blasting gun. Once I got down to bare metal, I sprayed it with Rust Mort - phosphoric acid with a handheld spray bottle then rinsed it with a fire extinguisher. I personally never use undercoating or Por 15. Once it's clean I use etching primer on bare metal and regular then primer n paint. Nothing ever comes back. I know someone who relied on Por 15 to do his truck. He didn't properly clean his rust problems and was told the chemicals would transform the rust. His frame broke in 1/2. Por 15 is a good (however, expensive) product. It's not a cure all.

 

[Vincent72Q]

I wouldn't put any paint designed for metal on any undercoating or seam sealer, as the rubberized stuff can flake off and take the paint with it.

Understood. Thanks for the reply

 

[Vincent72Q]

I would see if there is anyone in your area that could come out, mount your car on a rotisserie, wheel it out of the shop and either soda or dry ice blast the bottom to clean everything off. After that, spray the bottom with an epoxy primer to seal it, do any rust repair you need to and then spray the repair areas with the epoxy primer. You can have it tinted to replicate the red oxide from the factory if you want to get real fancy. After that, undercoat any areas that the factory did, or you want.

Unfortunately that is not an option. Wish it was.

 

[Vincent72Q]

You could do what many of us have done. Use an angle grinder with a wire wheel on those areas of concern. I recently put POR-15 on the underbody of my 73 Vert and am very satisfied with the results. Some areas were mirror clean, and a few still had some of the original primer/paint from the factory. I did use acetone to clean off anything that might still be on the metal before I applied the POR-15. Not everyone on this forum thinks POR-15 is a good product. I’ve had good luck with it. Remember, once you put this stuff on, nothing else can be applied to it unless you follow specific instructions from POR-15. If you want more info, send me a PM.

I was wanting to use POR-15 because it really hardens when it dries and i was hoping it would last. As we know grinding down an undercarriage is no small feat and I really dont want to have to do this again. Glad to hear yours turned out well. I keep hearing horror stories about it flaking off in sheets and I am just trying to make sure i do things right. I am limited with my setup and concerned it wouldn't grip as well if i don't clean it good enough.

 

[Vincent72Q]

Red Oxide? What red oxide.
I have a friend who also believes red oxide was used and put it on his 71 429 J code. Wrong, that was a Dearborn car.
Now, to be fair, I could be wrong if the car was from Metuchen, but I believe only up to 70 was red oxide used.

Mine definitely has red oxide primer. I've found it all over the car. 1972 Q vert built in Dearborn

 

[Vincent72Q]

The important part is to not leave any rust. I used wire wheels, wire brushes, physically scraped the old coating off with putty knives, handheld sand blasting gun. Once I got down to bare metal, I sprayed it with Rust Mort - phosphoric acid with a handheld spray bottle then rinsed it with a fire extinguisher. I personally never use undercoating or Por 15. Once it's clean I use etching primer on bare metal and regular then primer n paint. Nothing ever comes back. I know someone who relied on Por 15 to do his truck. He didn't properly clean his rust problems and was told the chemicals would transform the rust. His frame broke in 1/2. Por 15 is a good (however, expensive) product. It's not a cure all.

Not looking for it to cure rust. Just want a hardened protective layer over the undercarriage. I'm going to be grinding all of the rust spots down but having a hard time figuring out how to wash it down without bringing a hose into my shop. I most likely will not be using any etching acids or primers since the metal is old and ill be scuffing it with a grinder.
Cant imagine a frame breaking in half. It must've been pretty far gone to begin with

 

[rvrtrash]

Red Oxide? What red oxide.
I have a friend who also believes red oxide was used and put it on his 71 429 J code. Wrong, that was a Dearborn car.
Now, to be fair, I could be wrong if the car was from Metuchen, but I believe only up to 70 was red oxide used.

You could be right. I based my answer on my observation of my car. It has 73K miles, off the road since 1979, and is completely undercoated (Seattle district car). However there is a small spot by one of the rear shackles where it's bare, and it sure looks like a reddish brown color to me.

 

[Stanglover]

Mine definitely has red oxide primer. I've found it all over the car. 1972 Q vert built in Dearborn

Then I would have to think it's been repainted at some point in time.
I've owned 4 Dearborn built Mustangs, 2 71's and 2 72's, all fastbacks, and none had red oxide underneath, all black, well actually slop grey, which could be anything depending on what leftover paint was getting mixed together. My current 71 has never been repainted underneath, totally original, but when I dropped the tank to replace it, the underside of the trunk floor was in pristine condition and a dark blue/grey shade. I wish I'd taken a photo, but didn't think at the time.