Working on my '64 Skylark here and I'm noticing that I missed some black rust pits in the metal when I sandblasted over the summer. Unfortunately its now the dead of winter and not exactly sandblasting weather. Beyond that, I rented the big compressor and I don't have access to it anymore. What would be an alternative way to treat this stuff? Ospho & epoxy? Rust Mort? POR-15? Thanks!

First you need to wait for warmer weather or find a means to heat your garage to about 70 degrees.

I would use abrasives similar to these: https://benchmarkabrasives.com/collecti ... ine-5-pack
This will remove the heavy rust build up along those edges.

A DA with 80 grit should remove most of the surface rust.

After that I would apply Phosphoric Acid. Might take two coats but the rust should turn black when converted.

Once the rust is converted, apply more Phosphoric Acid and immediately scrub the surface with a red Scotchbrite pad using soapy water to neutralize the acid. Rinse with clean water and then blow dry with an air hose and maybe use a heat gun to be sure everything is dry.

From there you can wipe down with Solvent based Wax and Grease remover (spray on and wipe off with clean towel before it dries) if you think you need to.

With metal temperatures at 70 degrees or above, let flash completely and then apply two coats of Epoxy Primer. You will then need to keep it above 60 degrees for 24 hours.

JoeDirt wrote: POR-15? Thanks!

50 lashes for mentioning that product!

tomsteve wrote:

JoeDirt wrote: POR-15? Thanks!

50 lashes for mentioning that product!

I call it POOR-15

'68 Coronet R/T wrote:First you need to wait for warmer weather or find a means to heat your garage to about 70 degrees.

I would use abrasives similar to these: https://benchmarkabrasives.com/collecti ... ine-5-pack
This will remove the heavy rust build up along those edges.

A DA with 80 grit should remove most of the surface rust.

After that I would apply Phosphoric Acid. Might take two coats but the rust should turn black when converted.

Once the rust is converted, apply more Phosphoric Acid and immediately scrub the surface with a red Scotchbrite pad using soapy water to neutralize the acid. Rinse with clean water and then blow dry with an air hose and maybe use a heat gun to be sure everything is dry.

From there you can wipe down with Solvent based Wax and Grease remover (spray on and wipe off with clean towel before it dries) if you think you need to.

With metal temperatures at 70 degrees or above, let flash completely and then apply two coats of Epoxy Primer. You will then need to keep it above 60 degrees for 24 hours.

Thanks! Definitely answered some of my questions. Yes, warm conditions are a necessity. I "can" get the garage up to about 70 but it takes a lot of propane to do it and doesn't last long.

I have a couple follow up questions if you don't mind. How will I know that the rust is fully converted/removed with the Ospho?

And then how will I know that the Ospho has been fully neutralized when I'm scrubbing/rinsing?

Also should I/must I avoid getting the Ospho on other previously completed body repairs? I ask because I'm likely going to have to rinse and scrub the whole shell down, and there is one area on the right rear quarter that I've already cut, welded, filled and epoxy primed and it would likely get wet if I was scrubbing/rinsing the whole shell at once. Obviously I don't want to contaminate the primer and filler that I've already put down.

I use other preparations of phosphoric acid, but I'm not very convinced that you should leave behind any residual rust. That is, dark pits. I prefer to put the acid on, cover with plastic wrap, and let sit overnight. Then remove the plastic and wire brush the acid residue off. It may take a couple days of doing this, but eventually, there will be no dark spots or iron phosphate, in the metal. You can also just keep scrubbing with any of the acids to achieve the same results, but I guess I'm getting lazy in my old age.
Also, contrary to some of our esteemed colleagues, I use rust encapsulators, like POR-15. Mostly on the backsides of panels that have been repaired/welded, and floor and trunk pans, where it isn't easy, or desirable to remove all rust through blasting or acid. Been doing it for over 30 years, and my work tends to hold up well. I would never use it under anything that gets good paint on, though. Just like leaving iron phosphate (dark pits) behind, I don't trust it 100% to put a good paint job over it.

It doesn't need to be warm to Blast. I would get your own compressor first then buy a el'cheapo pressure pot Blaster and re-blast the areas in question. Pitted metal must be Blasted clean. I have seen treated pits turn black from Ospro and or other Phosphoric acid treatments then dug at them with a Pick to expose red rust under the black so don't expect miracles from any rust converter's.

Before using Ospro or other Phosphoric acid treatments go. I would first look at those made by Axalta or PPG cold galvanizing metal treatments that are designed to be used under Paint systems before others such as Ospro or the like. They are Not miracle rust converters purse BUT they do remove and convert light rust.

chopolds wrote:Also, contrary to some of our esteemed colleagues, I use rust encapsulators, like POR-15. Mostly on the backsides of panels that have been repaired/welded, and floor and trunk pans, where it isn't easy, or desirable to remove all rust through blasting or acid. Been doing it for over 30 years, and my work tends to hold up well. I would never use it under anything that gets good paint on, though. Just like leaving iron phosphate (dark pits) behind, I don't trust it 100% to put a good paint job over it.

For the most part, these areas aren't getting "good" paint on them and they won't be visible when the car is put back together. One area is the rear deck panel above the rear seat into the inside structure of the C-Pillars. The other is the window channels for the rear window.

These are some pretty intricate areas and would be really difficult to strip mechanically. They've only got light surface rust and they'll never be seen when once the interior is back in the car.

Eastwood claims their Rust Encapsulator Platinum can be used under bodywork and they even have a video of one of their guys using it on a pitted roof skin on a first gen Camaro and putting epoxy right over it.

I would NEVER use it like that, but that is some serious confidence in their product.

I'm not the biggest fan of these type of "encapsulator" products but might be something worth considering for some of these interior areas that don't get seen and won't affect the exterior paint job.

Doright wrote:It doesn't need to be warm to Blast. I would get your own compressor first then buy a el'cheapo pressure pot Blaster and re-blast the areas in question. Pitted metal must be Blasted clean. I have seen treated pits turn black from Ospro and or other Phosphoric acid treatments then dug at them with a Pick to expose red rust under the black so don't expect miracles from any rust converter's.

Before using Ospro or other Phosphoric acid treatments go. I would first look at those made by Axalta or PPG cold galvanizing metal treatments that are designed to be used under Paint systems before others such as Ospro or the like. They are Not miracle rust converters purse BUT they do remove and convert light rust.

I know it doesn't have to be warm to blast, but it's 18°F outside and blasting is miserable enough when it isn't cold ! There's about 5 inches of snow on the ground too. I haven't tried to run the blaster with my 35 gallon compressor. I'm sure it'd do it for a little bit.

I know what you mean about picking at rust pits and finding red rust underneath. I've done that and seen the same thing. I think the rust pits have to be really shallow for it to fully penetrate and convert the black rust and work the way it is supposed to.



I appreciate all of the replies here, everyone has been very helpful!

As the other guys have said, get it as clean and rust free as you can. I've had good results with Brunox. It's a phosphoric acid type product but in a epoxy like clear liquid. Worth you doing a read up on the product.