Gallery, Projects and General > How do I??
Phospmoric acid.
mattinker:
Hi,
Coming out of lurk mode! I am in the process of re-enforcing the steel structure of the building I live and work in. It's an industrial building that is fifty years old, steel frame that wasn't galvanised. I've welded in patches and bolted on re-enforcing plates on the bottom four inches of the pillars. My plan is to cast concrete around the bases as protection against rust and to fill in the masonry that I had to break out to get access. I have treated the steel with Phosphoric acid, after as much de-rusting/de-scaling as possible, my problem is, will the concrete react with the Phosphoric acid or should I paint before pouring the concrete?
Your thoughts would be most welcome! Regards, Matthew
awemawson:
Well the concrete is very alkaline and (obviously) the acid is very acidic, so they will tend to neutralise each other.
However steel in concrete shouldn't rust if covered by at least 40 mm - or at least that's the rule for re-inforcing bars in concrete - minimum 40 mm over cover - (to exclude the oxygen).
mattinker:
Thanks Andrew,
The rest proofing from burying in concrete was the aim, I suppose I'm a bit belt and braces, as I really don't want it to rust! I will probably paint over the phosphoric acid to separate it from the concrete.
No other suggestions? I'm not very good at Chemistry!
Regards, Matthew
chipenter:
Phosphoric acid leaves a hard glittery surface ideal for primer , red oxide will do both seal and stop rust .
mattinker:
--- Quote from: chipenter on November 25, 2019, 01:44:19 PM ---Phosphoric acid leaves a hard glittery surface ideal for primer , red oxide will do both seal and stop rust .
--- End quote ---
Thanks, I've been using phosphoric acid for a very long time, I've always had very good results with it. My problem is what reaction it might have with concrete. Lead oxide is no longer available here in France as a primer (house painters here used to mix phosphoric acid into metal primer here!).
Regards, Matthew
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