[TheForge] Phosphoric Acid

[Peter Hirst]

Repeated the procedure and got a different result?

You sure the products you used were exactly the same?  Phosphoric acid is a 
rust remover, and should have left the I beams bright, not black,  after 
cleaning off the acid.  A product called Ospho, which is reputedly 
phosphoric acid and some secret sauce, although I have heard it described as 
phosphoric acid alone,  is a rust converter which turns rust to a black 
polymer and makes a great sealer and undercoat.

If the railing was bright or mill scale, and you used just phosphoric acid, 
not rust converter,  without cleaning, acid residue could continue to etch 
the steel under the paint and break the paiint bond.  If you used a rust 
converter where there was no rust, you have prevented the pait from bonding 
at all.  Phosphoric acid alone  should have etched the bright steel and 
created a solid bond with any good metal primer, but I believe the acid must 
be either neutralized or rinsed off before coating.  And re powder coating? 
Is't it ungodly expensive there?  It runs about 100 per foot around here.
----- Original Message ----- 
From: "Cindy and James" <jallcorn at suddenlink.net>
To: <theforge at mailman.qth.net>
Sent: Sunday, June 29, 2008 9:31 AM
Subject: [TheForge] Phosphoric Acid


>
> All this about phosphoric acid, I have a question.
>
> Have any of you used it and then painted over it?  Exactly what was the 
> procedure and what was the long term result?
>
> I have some 200' of 8" and 12" I beams in my shop supported by 15' long 
> 5.5" pipe columns,  and all were significantly rusted when delivered from 
> the steel yard.  After installation, I wanted to paint and looked for 
> something to get rid of the rust, etc., and came up with phos acid. 
> Bought at local TSC store.  I painted it on w/ a 4 " brush and waited a 
> couple of days.  It turned black if I recall correctly.  Then I painted 
> with a coating of high gloss black equipment enamel.  That was about 4 
> years or more ago and it still looks great.  It is inside.
>
> Recently I built a balcony railing for a client and recalling my 
> experience with the I beams, etc., thought I would try that.  Well, that 
> was less than a year ago and the paint has started chipping off and rust 
> bleeding through on some parts of the railing, scrolls, bars, etc.  Also, 
> a very obnoxious white powdery substance is leeching out from 
> under/through the paint and running down.  You can wipe it off with your 
> finger.  I went back the last 2 days and wire brushed, scotch-bright, 
> sandpapered the thing, and repainted with flat black rustoleoum.  Took me 
> 8 hours, 1/2 of which was hanging on a ladder 30 ft up on the side of the 
> house!
>
> If I had had an inkling this would happen, I would have had it powder 
> coated or at the very least, hired a good painter.  And that is what I 
> will do if my repaint job fails (hire the best painter in the area).
>
> This is my deal and I feel responsible.  If it were 5 years, that would be 
> something else, but not 7 months!  I did all the ironwork in this client's 
> new $1.5+ home and everything else is great but this.
>
> Any ideas welcome.
>
>
> James Allcorn
> Bois D'Arc Forge Blacksmith Shop
> Paris, TX
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