Paint as good as hot dip galvanize

[civeng80]

Is there a paint as good as hot dipped galvanizing out there ? I have some existing painted steel which is at present inside that will be exposed to the outside atmosphere and must be painted to a standard as good as hot dipped galvanize.

 

[hokie66]

In my opinion, no. Applied high performance coating systems can provide excellent protection, with surface preparation the most important step, but hot dipped galvanizing is the premier coating.

 

[csd72]

The main difference is durability, properly specified galvanising will last a lifetime, paint needs to be redone every 10 or 15 years.

Try a zinc rich paint, these straddle the line between the two.

 

[JedClampett]

Or you could ude a belt and suspenders solution and paint hot dip galvanized steel.

 

[PEinVA]

Jed,
I think the OP was mentioning that the steel was existing already in place. Also, that seems like an idea that came from the department of redundancy department.


RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[csd72]

Jed, there are actually a lot of issues with painting over galvanising due to the pickling residue

 

[apsix]

civeng80
To answer your specific question (as I interpret it), yes you can find a paint system which will give similar protection as galvanising, IF it is not possible HDG the existing items you have.
If you can HDG it then do that, as it will be more robust and probably cheaper.

 

[HgTX]

If you can't HDG because the part is in place, you can use use thermal-spray metallizing.

A properly applied zinc-rich paint system can last a good long time. Best is inorganic zinc with no topcoat, if you don't care about color--there are test panels out there that have been up for decades and are doing fine. You need to make sure that the surface is cleaned to bright metal before you apply the paint.

Hg

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[DRC1]

ZRC makes a cold galvinizing compound. Is it as good as hot dipped? probably not. Iss it suffucient for your purposes? Probably. And is that not the right question to ask?

 

[hokie66]

civeng80,

I think you have the sense of comments here that no paint system is actually as good as HDG, which was your question. But if you have to provide a durable paint system to an existing structure, the most important thing is the preparation. As the existing steel is interior, it probably has only been painted with an architectural coating not designed for exposure. To get a durable coating, the existing coating would have to be removed. I would consult with one of the industrial coatings manufacturers for a suitable system. It will likely involve an epoxy zinc rich primer (not inorganic zinc, which is only for shop work), and top coats to complete the system.

 

[civilperson]

Epoxy paint systems can be the equal of galvanized with sufficient thickness.

 

[HgTX]

The steel is "at present inside that will be exposed to the outside atmosphere", and apparently flat panels at that. There's no reason they can't paint it with IOZ.

IOZ is difficult to apply in a field environment, but that does not mean it is not appropriate for field exposure. If you can get it on right, it's better than a multi-coat epoxy zinc system.

On the other hand, hokie66 is right in that if you have any doubts about how good a job they will do with surface preparation and paint application, you're better off with an epoxy zinc system (typically zinc primer, epoxy intermediate coat, and then urethane topcoat). Epoxy zinc is a rather forgiving coating.

Hg



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[HgTX]

p.s. I meant to add that Florida DOT has gone to all IOZ, even for field painting. But I haven't heard how well that's working out for them.

Hg



Eng-Tips policies: faq731-376

 

[civeng80]

Great comments from all. Confirms what I have in my mind.
Hokie66 epoxy rich zinc top coat with top coats sounds like the way to go with the existing steel (UBs) and hot dip galvanize the new steel which will be bolted onto the existing steel columns.

Many thanks.

Its great to be part of this group.

Cheers !

 

[hokie66]

And you can paint over the galvanizing, but be careful again with the preparation. Follow the manufacturer's recommendation. Had a case years ago where a urethane was applied to a galvanized spaceframe, failed adhesion tests, and had to be disassembled and taken back to shop for removal of the topcoat before doing it right. Much less of a problem if the galvanizing is aged.

 

[IFRs]

Where the paint ends and the HDG starts is where I would look for coating failure.

 

[structuresguy]

NASA and the Air Force use Inorganic Zinc coatings for all their exposed structural steel at Kennedy Space Center and Cape Canaveral Air Force Station. The steel framed launch towers are right on the beach, fully exposed to salt spray from the ocean.

I have personally done work on these towers. Some are quite old and still in very good condition. Some areas, which may have been more prone to standing water or poor drying, have shown some corrosion damage, though proper periodic maintenance could have helped these areas.

IO Zinc can be field applied, and touched up in the field. The critical step is proper sand blasting and time after blasting until painting. The steel needs to be blasted near white, and then painted immediately. This can be tricky for large areas in the field.

If I could not HDG steel, I would use IO zinc.

 

[hokie66]

I agree with others that the hierarchy is HDG, inorganic zinc, then other high performance systems. Both HDG and inorganic zinc can be overcoated to improve their longevity. While it may be true that inorganic zinc can be field applied, it is too tedious with too many contractor dependent variables for my liking. Field applied coatings are generally to repair deteriorated surfaces, and the more forgiving coatings like some of the Carboline products such as Carbomastic 15 are better choices in my opinion.