Question about Ospho, epoxy primer, deep rust

[nickwisconsin]

Brand new to the forum. I have inherited a classic car that has some underbody and frame rust. Car is otherwise in great condition so not doing a frame off.

I tend to think things through before starting, and sometimes this makes for a much longer project, but I want to do this right the first time. I have been experimenting with different mechanical rust removal methods, sandblasting, wire brush, angle grinder with a variety of attachments, etc. Since I am not doing a frame off, I will likely rely primarily on the angle grinder and wire brushes and stripping wheels. I have also spent some time with Ospho and evaporust. There will be places that I will not be able to get down to bare metal prior to epoxy primer and will likely rely on ospho to treat prior to priming.

My understanding is that Ospho will convert surface rust, but if the rust layer isn't very superficial, I would assume that under the ospho treatment there is still deep rust. Is that just eventually going to break through the primer and paint? My plan is to spray and let it soak in and convert and then prior to painting, re-wet with ospho, rinse off. On my test pieces I have noticed that even doing this leaves a white film. Is that OK to paint over or is that going to react with the epoxy primer?

Any thoughts on how to address rust within the frame? Spray ospho into the frame and rinse out? Use a product like Eastwood internal frame coating? Any strategies for spraying epoxy primer into a frame if I go that route? TIA.

 

[Chris_Hamilton]

First do a search here on Ospho using the keyword "ospho" and read up on all the information here about it. Lot of posts that go into detail about how to neutralize Ospho. In short to neutralize it you need to re-wet it with more Ospho, keep it wet (with ospho) for 15 minutes or so and then rinse. Using a wire brush and go over the area you are neutralizing to help break up the crud. Then rinse.
As for internal frame areas cavity wax works well. You can try flooding internal surfaces with epoxy, but not being able to prep them properly cuts down it's effectiveness. Cavity wax works well and sticks to all the surfaces. Do another search here on cavity wax and a lot of info will come up.

 

[Dean Jenkins]

Welcome to the forum! You will find a tremendous amount of good information here, and lot's of experienced folks willing to help.

You'll also find that there are many different approaches and opinions to particular situations. Lot's of different paths to success.

So, here is my opinion:

Without taking the body off the frame, it is quite possible that you just won't be able to get all the rust as well as you'd like.
And getting the rust out of the inside probably isn't going to happen.
At some point you will have to decide that it is good enough.
I agree with @Chris_Hamilton to use cavity wax.
Just get all the painting done on the frame BEFORE spraying the wax or you will have problems with fisheyes etc.

The consensus on the forum, and in my own experience is that media blasting is the best way to really get rust off.
You can get a spot blaster from Harbor Freight for pretty cheap and it works well for this type of work.
Coal slag is a great media for rust removal. You can get it at Tractor Supply. The Red Stripe works well in the Harbor Freight unit.

 

[nickwisconsin]

First do a search here on Ospho using the keyword "ospho" and read up on all the information here about it. Lot of posts that go into detail about how to neutralize Ospho. In short to neutralize it you need to re-wet it with more Ospho, keep it wet (with ospho) for 15 minutes or so and then rinse. Using a wire brush and go over the area you are neutralizing to help break up the crud. Then rinse.
As for internal frame areas cavity wax works well. You can try flooding internal surfaces with epoxy, but not being able to prep them properly cuts down it's effectiveness. Cavity wax works well and sticks to all the surfaces. Do another search here on cavity wax and a lot of info will come up.

The ospho research is what brought me here. I got a lot of great advice on how to neutralize. Thanks for the advice on cavity wax.

 

[shine]

there is no such thing as converted rust. covered up rust, purple rust and many other snake oil claims. surface rust is no problem as it will never rust thru. if you get rid of the dirt and sand in cavities you are good. the dirt holds the moisture letting the rust get out of hand. don't over think it .

 

[nickwisconsin]

Welcome to the forum! You will find a tremendous amount of good information here, and lot's of experienced folks willing to help.

You'll also find that there are many different approaches and opinions to particular situations. Lot's of different paths to success.

So, here is my opinion:

Without taking the body off the frame, it is quite possible that you just won't be able to get all the rust as well as you'd like.
And getting the rust out of the inside probably isn't going to happen.
At some point you will have to decide that it is good enough.
I agree with @Chris_Hamilton to use cavity wax.
Just get all the painting done on the frame BEFORE spraying the wax or you will have problems with fisheyes etc.

The consensus on the forum, and in my own experience is that media blasting is the best way to really get rust off.
You can get a spot blaster from Harbor Freight for pretty cheap and it works well for this type of work.
Coal slag is a great media for rust removal. You can get it at Tractor Supply. The Red Stripe works well in the Harbor Freight unit.

I know I won't be able to get all the rust off the frame as well as I would like. I have thought long and hard about a frame off. I don't have the facility, the equipment, or the skillset for that. The car is in my parent's shed 60 minutes away, so I do not have unlimited time to work on it. Plus - the car is pretty perfect except for underbody rust. I do realize there are going to be unseen areas of rust. It is a compromise, that is for sure. There are some mechanical things that I am doing. Brake system rebuild, new radiator, clean and paint engine bay, but nothing body or paint-wise. Thanks!

 

[nickwisconsin]

there is no such thing as converted rust. covered up rust, purple rust and many other snake oil claims. surface rust is no problem as it will never rust thru. if you get rid of the dirt and sand in cavities you are good. the dirt holds the moisture letting the rust get out of hand. don't over think it .

Doesn't it convert iron oxide to iron phosphate?

 

[MJM]

I 2nd Dean's comment about using a spot blaster for deep pits. I have a pot pressure blaster but I'll use my spot blaster for certain situations. It made short order for media blasting the trunk channel and lower cowell. I basically use it for pin point accuracy.

I modified my Harbor Freight blaster to hold more media for longer use. Yes, that's a one gallon milk jug that fits perfectly in the blaster reservoir.

 

[dhutton01]

I 2nd Dean's comment about using a spot blaster for deep pits. I have a pot pressure blaster but I'll use my spot blaster for certain situations. It made short order for media blasting the trunk channel and lower cowell. I basically use it for pint point accuracy.

I modified my Harbor Freight blaster to hold more media for longer use. Yes, that's a one gallon milk jug that fits perfectly in the blaster reservoir.

View attachment 22306

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View attachment 22308

Nice. I like that reservoir. I’m going to steal that idea

Don

 

[Lizer]

there is no such thing as converted rust. covered up rust, purple rust and many other snake oil claims. surface rust is no problem as it will never rust thru. if you get rid of the dirt and sand in cavities you are good. the dirt holds the moisture letting the rust get out of hand. don't over think it .

Reaction of rust with other commonly used chemicals results in a chemical reaction that does in fact convert rust to a different chemical. How much rust is actually converted is completely dependent on how long it's allowed to react, which goes for about anything.

 

[MJM]

Nice. I like that reservoir. I’m going to steal that idea

Don

You're too late to steal the idea. The Chinese have already seen my modification and are manufacturing an adapter to use one gallon orangejuice jugs. Suppost to be on the shelves at Harbor Freight spring of 2023.

 

[shine]

you can buy a rig to use on your pressure washer to blast with. works well with crushed glass.

lizer , in 50 years i have not witnessed a successful stopping of rust. i've seen all different colors and such but it always comes back.

 

[MP&C]

One of my first overall paint jobs was wasted because the owner had done the bodywork on his Model A, applied far too much ospho and did not remove any residue from the deep pits. My first experience with ospho, and questioned it as my gut told me this wasn't good. But it was OK, because his buddy did it all the time and had no problems. Once the car sat in the sun at all the car shows that year, the ospho collected in the pits activates and the chemical reaction starts outgassing. So what that looks like is little tiny circles of paint lifting. In less than a year. So my advise is that what you've been told about a spot blaster is on the money, and f**k what anyone's buddy says, get your advise from the paint manufacturer that made what you're spraying on the car. If you look up companies like Ospho, their website will proudly proclaim that it works with all paints, and then hides any disclaimer of spraying test panels on another page. Snake oil salesmen are in the business of selling snake oil, they could care less what peels. Get the correct info from your paint company.

 

[Lizer]

you can buy a rig to use on your pressure washer to blast with. works well with crushed glass.

lizer , in 50 years i have not witnessed a successful stopping of rust. i've seen all different colors and such but it always comes back.

Converting rust and stopping rust are two different things. Soak a rusty bolt in phosphoric acid overnight and you've converted the rust and it's now a nice clean bolt, but with time it will eventually rust again unless it's coated with something to protect it from the chemical reaction that causes rust in the first place.

I'm aware you know all of this. I just couldn't let your original comment slide

 

[shine]

you're a chemist Lizer and i know what your saying but i'm a painter of 50 years. i've seen every kind of wild failure you can imagine. not as much wizardry going on now days.
our problem is half of the hobbyist will not get it right. first summer and it blows up. i hate any kind of snake oils. 3m made a fortune and destroyed hundreds of cars with their purple rust. ospho will do wonders but you have to know what your doing.
i just popped the windows out of a 56 chevy that was ready to deliver. it is now a hull . nobody needs to go thru this. if it is not made to mix with the paint leave it in the cabinet and dont have anything on the bench not intended to mix in the paint. reducers on the left thinner on your irght. . only reason i dont like chemicals and resins discussed in mixed company. one poor bastard going thru this is enough.

Barry , you need to put the ospho tutorial up often.

 

[nickwisconsin]

I 2nd Dean's comment about using a spot blaster for deep pits. I have a pot pressure blaster but I'll use my spot blaster for certain situations. It made short order for media blasting the trunk channel and lower cowell. I basically use it for pin point accuracy.

I modified my Harbor Freight blaster to hold more media for longer use. Yes, that's a one gallon milk jug that fits perfectly in the blaster reservoir.

View attachment 22306

View attachment 22307

View attachment 22308

I have limited access to a capable Sand blasting setup, but it is at my inlaws 2 hours away. Up to now I've just been bringing small parts. As of this time, I can't get the vehicle up there due to the state of disassembly.

Sand blasting works great, but I worry that doing a sand blasting on a "non frame off" is gonna cause as many problems as it solves. Media in nooks and crannies and possibly getting where it shouldn't. I don't have an air compressor capable of producing enough air enough air for sand blasting at my parents place where the vehicle currently sits on jack.stands. I looked at the power wash media blasting setup's, but I have the same concerns using it on a vehicle that's intact.

 

[chevman]

People have varying opinions on the things they worry about, how about some pictures of the rust that you are worried about? It might be easier to handle than you think.

 

[Barry]

One of my first overall paint jobs was wasted because the owner had done the bodywork on his Model A, applied far too much ospho and did not remove any residue from the deep pits. My first experience with ospho, and questioned it as my gut told me this wasn't good. But it was OK, because his buddy did it all the time and had no problems. Once the car sat in the sun at all the car shows that year, the ospho collected in the pits activates and the chemical reaction starts outgassing. So what that looks like is little tiny circles of paint lifting. In less than a year. So my advise is that what you've been told about a spot blaster is on the money, and f**k what anyone's buddy says, get your advise from the paint manufacturer that made what you're spraying on the car. If you look up companies like Ospho, their website will proudly proclaim that it works with all paints, and then hides any disclaimer of spraying test panels on another page. Snake oil salesmen are in the business of selling snake oil, they could care less what peels. Get the correct info from your paint company.

Folks, this needs to be read 20 times.

I took a lot of flake when I banned a company
On this site, but IF you actually make stuff and not just slap a label on a can, there are no secrets in this business with the real manufacturers.

Here is how the private label works; this is a call I got from a big company that makes nothing, and they are way bigger than me.

"Our company would like you to consider making clear for us and could lead to you making more items down the road."
(I only do a label for two very high-end companies as not interested in stocking crap resins) but I listened.

"We want a quote on 10,000 gallons of a 4:1 clear to start."
Ok, a few questions what is solid content?
"Solids might be a good idea."
Ok, how about UV additives, any types and ratios?
" that might not be a bad idea to add some."

Folks, this is how it works; it's all about the profit.