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Pickling and Phosphating a project made of steel

In my home shop I build doors for our barns and other necessary items from steel. Sometimes the items stand around for a few months while some other project interests me. During this time, a layer of rust will build on the item. I like to remove this rust and any mill scale with muriatic acid [affil links] to get down to the bare steel. I use the muriatic acid full-strength in a well-ventilated area, wiping the acid on the item with a rag. After the muriatic acid wash, I rinse the item well with water and allow it to dry, or dry it with compressed air.

Now, here's my problem. I want to follow-up this pickling process with a home-brew phosphating process, followed by traditional painting with primer followed by topcoat. Why Phosphate if I'm going to paint anyway, you ask? Well, the painted steel parts on my John Deere equipment are coated with something that looks like a phosphate coating before they are painted. Wow, does that coating ever slow down the progression of rust! Any scratch that goes through the paint surface will eventually allow the base metal to rust, but this phosphate coating slows the rusting to a virtual crawl. That's what I want to duplicate.

What can I do to approach this phosphate coating process? Anyone out there have any ideas?

Bruce Smith , P.E (electrical)
user - Monticello, Iowa
February 5, 2008

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naval jelly [on eBay or Amazon] is probably the closest thing to a phosphate coating that you can apply simply and in a single step. It's not as good because you are not getting constant solution replenishment as you would with spray or immersion phosphate, but I think you'll see a worthwhile improvement in resisting rust.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 6, 2008

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February 8, 2008

Simple and effective rust converter [on eBay or Amazon] :
20 gm tannic acid [on eBay or Amazon]
15 ml phosphoric acid
1 lit water
Solution can be painted or sprayed on object(oxide and grease free!).When it is dry you must clearcoat it(or paint).Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia