Author Topic: Phosphoric Acid (Read 19080 times)

Matt G · « **on:** October 10, 2015, 10:46:37 PM »

Has anyone used Phosphoric Acid to convert surface rust on their chassis?
If yes, what did you follow up with to protect afterwards? Assuming that you did use something...
🍺Cheers.

metalhead · « **Reply #1 on:** October 11, 2015, 07:38:25 AM »

Not on my Vette, but yes I've used it. Wire wheel as much rust off as you can first, convert, and paint. I don't think it will hold up long, particularly on a chassis, if it's not coated over with paint (or similar).

Matt G · « **Reply #2 on:** October 21, 2015, 01:36:05 PM »

Looking for advice with regards to absolute comfort that the inside of my chassis is protected. I have previously sprayed phosphoric acid in there, however I didn't seal it afterwards. I was thinking of spraying a tanic acid solution (converter and sealer), and then cold gal. When you guys do your frame off restos, what/how do you treat the inside of your chassis? I know that you guys are more detailed and anal than me, so I'm pretty sure that you don't just give the outside a quick spray of black and call it done.
any advise or experience on this out there?

Matt G · « **Reply #3 on:** October 24, 2015, 11:28:23 AM »

Maybe I should simplify my question. Anyone who's done a body off resto.... what have you used to protect the inside of your chassis?
Any tips or tricks would be appreciated (before I go with my typical "what the hell, let's try it" approach)
Cheers

bootlegger · « **Reply #4 on:** October 26, 2015, 11:16:07 PM »

If you use any type of acid on metal you need to nuetralise it with water otherwise you will create more rust.
If you want to coat the inside of the chassis any epoxy paint will do such as kill rust.
POR spruick about how great there product is at preventing rust but its expensive and once done your pride and joy will never experience the hard life it had when it was ten years old.
So my point is get rid of the rust and just fill it with paint.

sirfixalot · « **Reply #5 on:** October 27, 2015, 08:20:47 AM »

Was at a mates place last week he had vet chassis hot dipped galvanised about $250 down side was he had to run a tap through all threads in chassis, was then going to paint with black paint similar to POR chassis paint

Scott · « **Reply #6 on:** October 27, 2015, 08:33:39 AM »

All the landrover guys just spray the inside of the chassis with cavity wax or lanolin. Not as permanent, however for a vette you'd only have to do it once every 5 years at most and it wouldn't take long. Probably 2-3 beers worth if you do it right ;)

bfit · « **Reply #7 on:** October 27, 2015, 10:18:17 PM »

I'm thinking it's 40 years old and in reasonable condition ,
Will it go another 40 years, if nothing is done.

Hot dip gal I've seen it done but the heat of the gal pit weakens the steel. I wouldn't go that way .
But
A few sacrificial anodes ! Bolted to the frame, well! that's easy and works
Bfit

StephenSLR · « **Reply #8 on:** October 28, 2015, 09:52:09 AM »

POR-15 is mentioned a lot in the other forums; I haven't used it myself; KBS in Aus. make a similar product that's cheaper.

If you don't mind going to another forum; there's a thread on it here:

http://www.gmh-torana.com.au/forums/topic/6971-por15-and-other-rust-convertors/

s

gtc · « **Reply #9 on:** October 28, 2015, 07:20:32 PM »

Quote from: StephenSLR on October 28, 2015, 09:52:09 AM

POR-15 is mentioned a lot in the other forums

I have used POR-15 for many years. If you follow the instructions and use their Metal Ready rust converter and surface etcher product first, then you'll get a great result.

Matt G · « **Reply #10 on:** October 28, 2015, 11:28:15 PM »

Thanks guys. Great tips and good hints. I'm an engineer, so the geek in me loves the sacrificial anode idea. I looked at the POR and the KBS stuff and their etchers look to be phosphoric acid based. They're key is that they clean and airtight coat everything afterwards.
The only tannic acid base looks to be the base for the all in one converter and sealers.

Here's my plan:
1. Stick my new 5m borescope up through my chassis and video record so that I can make sure that step 2 and 3 will work.
2. Spray (despite recommendations) a tannic acid base converter and sealer with my "u-beaut" home made internal spray system..... (garden sprayer plus 1/4" tube, valves and micro mist spray nozzle) through my chassis. Repeat and concentrate per borescope findings.
3. Spray cold gal inside until a solid sealed coat is everywhere!!!
4. Maybe add a lump of magnesium or zinc as a sacrificial anode, or repeat the spray process with lanolin or fish oil...
I'm travelling (work) a fair bit in the coming weeks, but will aim for the end of Nov for the rust conversion sealer part, and then add the zinc cold gal in Dec.
thanks again for everyone's feedback, links and experience!

StephenSLR · « **Reply #11 on:** October 29, 2015, 07:37:26 AM »

Quote from: Matt G on October 28, 2015, 11:28:15 PM

I'm an engineer, so the geek in me loves the sacrificial anode idea.

I'm an engineer too (Mechanical); the sacrificial anode idea is great on ships as you have them sitting in salt water (electrolyte); not such a great idea to sit your car in salt water though, lol. From what I hear they're either bogus or don't work so great.

Just googled and there's a debate on this here;

https://www.newscientist.com/blog/lastword/2007/08/save-our-cars.html

s

Vettech · « **Reply #12 on:** October 29, 2015, 10:30:54 PM »

Your correct Steve, sacrificial anode is good in liquid environments with complete immersion. In the good old days people used "fush oil", sorry I mean "fish oil", this is Oz where we speak the Queens English. Stinks like hell, but maybe they have stuff today that is sanitized.

Vettech · « **Reply #13 on:** October 29, 2015, 10:38:49 PM »

Oh, and my understanding of phos acid is that it only works on rust, not on clean steel, all loose rust must be removed , the hard rust will be converted to another compound that is inert. At completion it must be washed and neutralised, putting it inside the frame I would only consider if you have plenty of access and can flush/wash, drain and dry thoroughly. Best of luck.

bfit · « **Reply #14 on:** October 29, 2015, 10:58:54 PM »

Mmm rust of iron and steel 4fe+3O2

A fellow some time back would say. quote why is it so?
In a car
We have steel air ( 20% oxygen )we have humidity, and rain and we have a battery that uses the chassis as part of its electrical system.

So how do we end up with 2fe2O3 ? ( i can't write that corectly on my iPad )

Bfit

StephenSLR · « **Reply #15 on:** October 29, 2015, 11:03:38 PM »

Quote from: Vettech on October 29, 2015, 10:30:54 PM

In the good old days people used "fush oil", sorry I mean "fish oil", this is Aus. where we speak the Queens English. Stinks like hell, but maybe they have stuff today that is sanitised.

They use cavity wax these days.

s

Vettech · « **Reply #16 on:** October 30, 2015, 08:29:42 PM »

Rust is complicated Bfit, be it Fe (OH)3 or FeO(OH) or Fe2O3.H2O but it boils down to bear steel, water and some spare oxygen, rust can happen any time, since normal air will have dissolved water molecules in it. If any one figures out how to stop it they will be either shot dead the next day or be multi multi millionaire.

Vettech · « **Reply #17 on:** October 30, 2015, 08:31:51 PM »

Cavity wax !?.... ummm I wonder.

Matt G · « **Reply #18 on:** October 31, 2015, 01:51:12 PM »

More good tips guys. Good Link Steve. There was a good comment that indicated that the zinc would work regardless of the emersion. My understanding of the emersion is that it helps the flow of current (salt bridge), but provided you have a good contact, the solution is not required. Back when I did my Eng (Mech also Steve), I thought of doing the pulse current idea (without the need for a sacrificial), however a guy in the link indicated that on a car chassis (because it's relatively thin), you would need a whopping big current for it to practically work. probably not a good idea on a car that depends so heavily on its chassis for earth....

Sounds like there's no sure solution, except to coat the crap out of it and hope that you've sealed out all moisture and all air. you know that even if I do a totally awesome job at coating the inside, and at completely sealing off any chance of internal corrosion, that I'll probably just set up another part of my Chassis, or steering, or diff, or something else to corrode - now that my chassis isn't the more exposed sacrificial part.... Even worse, I'll probably set up a beautiful little crevice corrosion environment, and I'll rapidly rust through somewhere hidden and completely unexpected!!

Then again, Like Bfit said, 40 years gone... Probably nothing to worry about and another 40 years will fly by without any signs of anything serious. I'm probably just being over pre-cautious!
Thanks again, I'll let you know how I go.
Cheers

Matt

StephenSLR · « **Reply #19 on:** October 31, 2015, 02:20:57 PM »

Quote from: Vettech on October 30, 2015, 08:29:42 PM

Rust is complicated Bfit, be it Fe (OH)3 or FeO(OH) or Fe2O3.H2O but it boils down to bare steel, water and some spare oxygen

... and it happens at the interface between water and air, not underneath the water. i.e. when the door drain holes would block up and the door fills with water; you would notice the rust occurring up higher, right on the water line; the submerged area would be relatively rust free.

s