Phosphoric Acid Rustproofing PROBLEM!!
Thread Starter
Melting Slicks
Joined: Feb 2006
Posts: 3,105
Likes: 96
From: Sunrise FL
Phosphoric Acid Rustproofing PROBLEM!!
Been etching sections of my frame with phosphoric acid for a while. Let dry overnite. The last time (after sandblasting) every time I wash off the acid a thin coat of rust forms in 5-10 minutes. Tried 3-4 times, same problem 
Previous rust removal was mostly wire brush and grinding with great results.
Once a good phosphate coating is down do you still need to prime???
TIA Mike
Previous rust removal was mostly wire brush and grinding with great results.
Once a good phosphate coating is down do you still need to prime???
TIA Mike
Drifting
Joined: Nov 2003
Posts: 1,680
Likes: 68
From: Towanda KS
Why are you using acid if you have a sandblaster? There is no need to etch metal following sandblasting.
If you feel you must, then rinse the acid with a soda water mixture. I mix a 1 pound box of baking soda in 5 gallons of water. This neutrualizes the acid and slows down the rust formation. This is especailly important for areas inside the boxed frame. Otherwise rust will continue to prosper.
You still need to dust a coat of primer over bare metal as soon as it's dry and frankly I wouldn't be using acid at all on a frame unless It was done professionally by dipping the complete frame into a netrualizer following acid etch.
tc
If you feel you must, then rinse the acid with a soda water mixture. I mix a 1 pound box of baking soda in 5 gallons of water. This neutrualizes the acid and slows down the rust formation. This is especailly important for areas inside the boxed frame. Otherwise rust will continue to prosper.
You still need to dust a coat of primer over bare metal as soon as it's dry and frankly I wouldn't be using acid at all on a frame unless It was done professionally by dipping the complete frame into a netrualizer following acid etch.
tc
Le Mans Master
Joined: Apr 2005
Posts: 6,349
Likes: 419
From: Seattle Area WA
That "rust" is the phosphoric acid wash doing it's job, what should be happening is the forming of a light coat of zinc phosphate that protects the metal from moisture, it should look kind of brownish gold, now just primer it after it dries.
Last edited by Scott Marzahl; May 15, 2007 at 04:12 PM.
Drifting
Joined: May 2005
Posts: 1,307
Likes: 10
St. Jude Donor '09
I also agree with Scott. First wash off the part to remove the converted rust then reapply the phoshoric acid (very light clean rag). Once dry you can tack the part and paint without the second rewash.
Remember also to dilute the phoshoric acid after use and use it as a plant fertilizer. There is a strong concentration of iron oxide and phosphates. Best not to pour down the drain since being a fertilizer (phoshates) it's not the best for lakes and rivers (algea).
John
Remember also to dilute the phoshoric acid after use and use it as a plant fertilizer. There is a strong concentration of iron oxide and phosphates. Best not to pour down the drain since being a fertilizer (phoshates) it's not the best for lakes and rivers (algea).
John
Safety Car
Joined: Mar 2001
Posts: 4,359
Likes: 116
From: AUSTIN Tx
Mike,
You are confusing phosphoric acid and a phosphate treatment. The phosphoric acid is simply for removing rust, while the phosphate treatment will prevent rust on bare metal for an extended peroid of time. I use a phosphate rinse on all my blasted parts if I am not painting them imediately, and all my blasted parts that are going to the powdercoater get the rinse since I never know how long they are going to let the parts sit around before working on them. I have phosphate treated frames, and they are still rust-free 2 months later! I buy a commercial grade of phoshate, but the stuff that Eastwood sells is the same thing, you just have to mix the powder with water. It is pretty simple to do, just rinse the parts in the phosphate solution and let them air dry.
Regards, John McGraw
You are confusing phosphoric acid and a phosphate treatment. The phosphoric acid is simply for removing rust, while the phosphate treatment will prevent rust on bare metal for an extended peroid of time. I use a phosphate rinse on all my blasted parts if I am not painting them imediately, and all my blasted parts that are going to the powdercoater get the rinse since I never know how long they are going to let the parts sit around before working on them. I have phosphate treated frames, and they are still rust-free 2 months later! I buy a commercial grade of phoshate, but the stuff that Eastwood sells is the same thing, you just have to mix the powder with water. It is pretty simple to do, just rinse the parts in the phosphate solution and let them air dry.
Regards, John McGraw
