killing rust with phosphoric acid ?

I read about using phosphoric acid to remove rust from sheet metal and when I went to buy some I found it had to find and then I found out it comes in different % of strength.Do I need to get full strength or is less% better? My Lincoln has some rust I would like to kill before I paint. Some of the pitts are pretty deep and I don't want to have it come back after my body/paint work. I'm really grateful we have this forum and the wealth of knowledge we can help to p*** on.

 

the acid works if you have a tank and submerge the parts in it for a few days, it will remove all the rust

but other than an actual acid dip, painting the acid on doesn't give good results

if you have small parts, you can go to your local hardware store and buy a quart or gallon of muriatic acid, it's used to clean concrete and stonework- get a plastic tank, mix it 50/50, and submerge the parts in it- just so you know the fumes that come off this stuff is very strong and will burn your lungs, it has to be done outside with a mask on, away from any homes or kids, etc.

if you have large panel areas to derust, you should be sandlblasting it

 

Sand it and naval jelly the pits. The gel consistency will make it stick to panels. If you use liquid acid, it'll work but constantly drip off and need reapplied.

Don't let it drip onto concrete. You'll have pitting within weeks.

good luck

 

Yes,scrounger is right about the fumes from muriatic acid.I have seen it cause wrenches hanging on the wall to start rusting the next day after the fumes p***ed over them,very strong stuff,even worse than Taco Bell "GAS"!! A friend of mine left some small parts in it for a few days(forgot about them),went back,and they had completely dissolved! If you are careful with muriatic acid it works well on small parts,i check on them every few hours.If you don't have a way to media or lightly sandblast,you can clean up the rust with a wire brush,grinder and use petroleum jelly,wash off with water(follow instructions on bottle) dry,then apply Ospho.I apply a very light coat of Ospho,let it dry a few minutes,then wipe off the excess with a clean paper towel.Let it dry until the next day,scuff it with a scotch brite pad,then apply a sealer such as PPG's DP product.I have been using this "system" for years with great results.Hope this helps.K.J.

 

I think you will only be able to buy it at a certain strength..like 10 or 15 % or something like that..you wont be able to buy it any stronger, at least not at any home store or commercial outlet store..

it will do the trick anyways..but i would go for the other alternatives first

here is some info i found on the Net
Phosphoric acid may be used by direct application to rusted iron, steel tools, or surfaces to convert iron(III) oxide (rust) to a water-soluble phosphate compound. It is usually available as a greenish liquid, suitable for dipping (acid bath), but is more generally used as a component in a gel, commonly called naval jelly. It is sometimes sold under other names, such as "rust remover" or "rust killer." As a thick gel, it may be applied to sloping, vertical, or even overhead surfaces.

After treatment, the reddish-brown iron oxide will be converted to a black iron phosphate compound coating that may be scrubbed off. Multiple applications of phosphoric acid may be required to remove all rust. The resultant black compound can provide further corrosion resistance (such protection is somewhat provided by the superficially similar Parkerizing and blued electrochemical conversion coating processes).

Following application and removal of rust using phosphoric acid compounds, the metal should be oiled (if to be used bare, as in a tool) or appropriately painted, by using a multiple coat process of primer, intermediate, and finish coats.

Care must be taken to avoid acid burns of the skin and especially the eyes, but the residue is easily diluted with water. When sufficiently diluted, it can even be nutritious to plant life, containing the essential nutrients phosphorus and iron.

 

I got a '32 Roadster quarter blasted and he did not get in where the small pit have began so that's the only place where there is rust left. I was going to look into acid to try to get the rest out. The jelly stuff sounds like it may work. How do you neutralize it after wards?

 

I found Phosphoric acid in 85% strength at a commercial distributor for $36.00 a qrt. but I think the wire brush/navel jelly thing sounds good.If I can wash it off with water and not hurt the lower painted areas. This is on the roof that was covered with a vinyl top. The rest of the car is great and won't need painting. P.S. got started on the 31 rpu 4 port Riley again and am getting ready to send my B engine out for the overhead conversion work and rebuilding. Can't wait to suprise some v-8 cars with the banger pickup.

 

I use oxalic acid. It doesnt attack anything except rust so you can leave the panels in for as long as you like. It seems to coat the panel too so you dont need to paint it immediately. I have some parts on my coupe that have been left bare for weeks and not rusted which is amazing in our climate.

I put half a dozen panels in and then leave them until i'm ready for the next one.

The beauty of this approach is you can derust the panel, take it out and repair it, trial fit it whilst you set up other things then chuck it back in the bath when your ready to paint.

see here
http://www.nsra.org.uk/newforum/showthread.php?t=16114&highlight=oxalic+acid

 

I have done this for years. Stripping parts to bare metal then scrubbing the parts with a 50/50 mix of water & pa.It will keep the parts rust-free for years. Just MAKE SURE u scrub the pa residue off before priming with soap& water. If not the epoxy primer WILL NOT adhere. I learned the hard way! I hammer& dollied out a 54 merc fender used a lil filler and put 3 coats HOK epoxy primer. The epoxy peeled in areas i must have missed with the rinse and had to go back down to bare metal again!No more for me.

 

Yup.

You can find it in wood bleach products like the link.... but it's getting hard to find.
http://www.dap.com/product_details.aspx?BrandID=155&SubcatID=24


On the other hand BAR KEEPERS FRIEND can be found almost anywhere (grocery store, target, etc.)
http://barkeepersfriend.com/BarKeepersFriend_powder.htm