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Protective Coating for a Galvanized Steel Building

05/10/2013 8:49 AM

I am searching for the right protective coating system for a 40' by 80' galvanized steel quansa hut that was built around 26 years ago. It is situated near a lake (fresh water) and used to store equipment and a boat. The galvanize appears washed from rain and snowmelt and rust is developing on several of the arches 7 to 10 feet above ground level. I have talked to several suppliers and given a variety of solutions.

I need to find a system that I can be confidant will adhere to the galvanize and not flake or peel off prematurely.

I appreciate any comments that you might offer.

Thanks, Wayne

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#1

Re: Protective Coating for a Galvanized Steel Building.

05/10/2013 10:11 AM

It has been many decades since (whole-house) air conditioner manufacturers suffered the hard lesson of learning how NOT to paint galvanised housings.

The zinc coating tends to be not only very 'slick', but also alkaline in nature, and thus, oil based paints do not work well due to suffering from saponification.

Go to your nearest International Paint, Sherwin Williams, or other (professional) supplier of protective coatings and discuss your need with them, in YOUR particular environment.

They all send (at least some) of their personnel through the very fine Coatings courses offered by NACE International and/or The Society for Protective Coatings.

Needless to say, PROPER surface-prep WILL be just as important as your product of choice ... one MUST "match" the other...! (Not all coatings call for the identical-same surface PROFILE and/or Surface Cleanliness Standard.)

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#2

Re: Protective Coating for a Galvanized Steel Building.

05/10/2013 10:21 AM

ndt-tom gives good advice.

The only thing I'd add to reinforce his admonition that surface preparation is important, is to say the best, most expensive coatings are ONLY as good the surface over which they are applied.

A clean surface with some "tooth" is the best, most receptive surface to have.

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#3

Re: Protective Coating for a Galvanized Steel Building.

05/10/2013 10:28 AM

I would recommend applying a primer of Zinc Chromate. I use it regularly on galvanized piping systems. It is not a top coat and will then need to be painted.

See this.

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#4

Re: Protective Coating for a Galvanized Steel Building.

05/10/2013 10:56 AM

As lyn says; "with some "tooth" has been a mandate ever since the US Navy determined that THAT (blasting) was the ONLY way to insure 'paint' (protective coating) staying in place on our ships.

Towards that end, MUCH study has been done to determine the BEST Surface Profile for each different coating (different grits of shot vs sand vs grit vs other media achieve different profiles using different equipment/nozzles/pressures). Though the manufacturers themselves do much of said testing, some credit must go to the "Hi-Tech" polymer chemists themselves who get involved in every aspect of coatings development; right down to building-in (designing-in?) of di-pole attraction between some coatings and specific substrates.

Taking-on such a project might warrant investing in a bit of (personal) research and tool investment. With regard to achieving the PROPER profile, in order to meet the coating Specification, google "Surface Profile Comparator" and "Profile Tape", and follow a number of links from there...()

Wishing you success!

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#5

Re: Protective Coating for a Galvanized Steel Building.

05/10/2013 2:03 PM

My favorite is aluminum paint. Great for rust prevention, a vinegar wash before should prep the roof. Quite common and popular for a long time. Easy to touch up and re-coat if necessary.

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#6

Re: Protective Coating for a Galvanized Steel Building.

05/10/2013 4:36 PM

Additionally . . .

Galvanizing (versus aluminizing or titanizing) creates several distinct layers, on and within a steel surface:

There are many 'Happy-to-Help' people out there who will be glad to share their advice. Sadly, much of such 'free' advice is about worth what you paid for it (nothing!).

You *DO* want to be careful during surface prep to NOT damage the existing zinc any more than necessary.

You *will* find a good deal of sage advice HERE ... and also HERE.

Note (at the 2nd link) the reference to Alkyd paints [lower-part of page, between Acrylics and Asphalts]. If memory serves me at all, I do not believe that aluminum paint tends to give the best results in the long run.

Also, some good advice in there regarding the right kind of blast medium to use (if you do, which you ought). Do NOT forget to insure a proper follow-up WASH, to insure eradication of any invisible contaminants that the blasting leaves behind.

The "Paint Spec" should advise maximum permissible chlorides, sulfurous compounds, etc (which relate to the NACE SC / 'surface cleanliness' Standards) ... and there are SCAT test kits available for testing same (try google). "Fun", and very informative to try these things occasionally!

Again, best of luck ~ (Post a picture afterwards!)

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#7

Re: Protective Coating for a Galvanized Steel Building.

05/11/2013 3:41 AM

Many good comments so far. Ignore those that give a specific type of coating. As you have been told the base MUST be suitable for the protective top coat. For example, an etch primer cannot be used before a cold galvanizing coat ( this is a generalization ) as the residual etch will eat the zinc in the top coat. My personal preference is for a zinc based product to sit better with the remaining galvanizing.

Jim

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#8

Re: Protective Coating for a Galvanized Steel Building.

05/11/2013 7:30 AM

The zinc coating on the original building has done its job of providing anodic protection all these years. Replacing the coating with a paint is certainly an option, but in the meanwhile, you might look into other methods that include attaching sacrificial anodes to the surface (like they do in hot water heaters), or running a small electrical current through the building shell (like they do to prevent corrosion of steel ships). You are still receiving some protection from the remaining zinc, but its life is limited.

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#9

Re: Protective Coating for a Galvanized Steel Building.

05/11/2013 10:13 AM

26 year old Galvanized Sheets.

As much prep that goes into it, it might just be as cost effective and cheaper to just replace the old sheets with new ones and leave it at that.

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#10

Re: Protective Coating for a Galvanized Steel Building

05/11/2013 5:08 PM

Unfortunately and realistically speaking your siding has ran its life course.

You can scrub and paint it all you want but the fact is you will not get every single inch of rusted metal fixed and once rust sets in its like cancer to metal buildings and it always gets worse.

You can cover it for a while but eventually it just comes back from right under the new coating until there is nothing to recoat.

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#11

Re: Protective Coating for a Galvanized Steel Building

05/12/2013 10:51 AM

Wash the building with bleach to get all the mold and milldew off, rinse with clear water, wash with white vinegar diluted 1:1 with clear water, rinse with clear water, treat rusted areas with phosphoric acid product like OSPHO, rinse with clear water, paint with Cold Zinc Galvanizing Compound, paint with iron oxide primer, paint with Rust-Oleum Professional High Performance Protective Enamel in your favorite color...good for another 25 years.

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#13
In reply to #11

Re: Protective Coating for a Galvanized Steel Building

05/14/2013 7:34 AM

I mostly agree with what you propose except for the rust conversion with phosphoric acid and then coating with cold galvanizing. Some manufacturers of cold galvanizing ( zinc rich paint ) warn against this pretreatment nowadays. They instead have a primer of their own that is compatible with their top coat.

Jim

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#12

Re: Protective Coating for a Galvanized Steel Building

05/13/2013 11:00 AM

Thank you to everyone for your comments and links! It's not the cut and dry system that the suppliers would like to make one believe. Thanks again for all your help. WC

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129CBRider (1); Janissaries (1); JIMRAT (2); lwcarruthers (1); lyn (1); mike k (1); ndt-tom (3); tcmtech (1); welderman (1); WJMFIRE (1)

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