Rusted CS Handrails: Will 20% Phosphoric Acid Spray Stop Rust?

[racookpe1978]

I have a number of rusted CS handrails with various amounts of ornamental iron welded on (causing many tiny details and rust pockets where it will be impossible to get a clean surface with sandpaper, brushes, grinding wheel, flapper disk, etc.) to repair for our church. Sandblasting or 100% equivalent commercial/professional prep is ruled out by the expense.

Commercially, phosphoric acid is available from Home Depot (and other places) in a 20% solution: The ads claim "Must for Rust" converts the surface rust to a hard "something" (cleverly not specified!) that can be painted over without further prep work.

If it is so good in stopping rust at the "house" level, why don't I see this solution being professionally in the power plants and refineries or bridges that are rusting out?

If the phosphoric acid is applied (hand sprayed) to these railings, any other precautions you recommend before priming and painting the rails after my weld repairs complete? I'll have a combination of older painted surfaces, older rusted surfaces, and new metal repaired areas.

I was planning on priming with a spray-on zinc primer, then 2 top coatings of black.

 

[KENAT]

I used similar stuff on some car bodywork touching up I did. I wasn't overly impressed by the results but in fairness I'm not sure the subsequent filling & painting etc. I did on it was the best.

Don't products like Hammerite claim to merrily paint over rust so long as the loose stuff is knocked off? Would this be adequate in your situation?

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[racookpe1978]

Hmmmn.

Might work, have not heard of it before. Web info is skimpy, but their web site doesn't seem to have any US outlets or sales staff. (Other than amazon.com or the like.)

(Would you buy the "used paint" or the "new paint" from an anonymous Amazon seller? 8<)

 

[MikeHalloran]

The rust conversion coatings work great, on rusty iron/steel.

They work a lot less well on shiny/bright iron/steel.
... because they work by converting the rust into a more stable compound, but they can't do that if there's no rust to work with.

So you have to get the metal super-clean, and then ... let it rust a little.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

If there are no time restraints I would treat the heavy rust and the treat the whole rail.
Get a product like either Ospho, 75% H3PO4, and apply full strength to the heavy rust spots, let stand over 24 hours, wash with the treated areas water. or you might be able to treat the entire rail with full strength acid from the bottle. The phosphoric acid will act as a cleaner an wash primer. If you are going to use a cold galvanizing coating get a good. expensive, brand.
Make sure your topcoat is compatible with the cold galvanize.

We use a coating called ZRC when it come to cold galvanizing.
The link to ZRC has information on topcoats for their products.

http://ospho.com/

http://www.zrcworldwide.com/

 

[EdStainless]

The ZCR is a great product.
There are rust conversion primers available.
Contact a local coating specialist (don't call it paint) and see if he is willing to give you some advice (since it is charity work).
There are special combinations of treatments/coating meant for this type of application. These may be expensive but they hold up very well.
Don't go home brew, you will be doing it again in two years.


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Plymouth Tube

 

[blacksmith37]

As noted; you want "conversion coating" , not phosphoric acid. Conversion coating contains Mn and other stuff. There has got to be a lot of info at NACE and the SSPC (steel structures painting council),Napco, Carboline, Ameron, Wis PC, etc, on conversion coatings. My recollection (30+ yr ago) , it was not worth putting a zinc rich primer over a conversion.

 

[KENAT]

racookpe1978 Hammerite's really common in the UK, not quite so here but I swear I saw it on Walmarts shelves a few weeks ago which is what made me think of it.

I'm not claiming it's going to do an absolutely awesome job but given the circumstances might be a good cost/benefit trade off.

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