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PU top coat on epoxy paint (over galvanized pipe)

PU top coat on epoxy paint (over galvanized pipe)

PU top coat on epoxy paint (over galvanized pipe)

(OP)
Hai all,

I'm working on waste water project right now, and the project site is around 33 deg C with 90% humidity. That is why we require our contractor to apply Polyurethane on top of epoxy layer to avoid chalking.

But I wonder if this also applies for Galvanized surface?
Which one of following spec is more suitable in your opinion for coating of galvanized pipe (utility water application):

  A). No primer (only galvanized surface) - Intermediate : MIO 2 pack epoxy 200 micron (100 x 2) - Top coat: Acrylic 2 pack polyurethane 100 micron, OR

  B). Organic Zinc Paint - Epoxy for Galvanized Surface (Intermediate) 30 micron - Epoxy paint for top coat (30 micron).

I personally think that option B is enough, but then again my adviser says that in general epoxy layer has to be protected with PU layer.

So which option is best? A or B or you guys has other idea on this?

Kind regards,

RE: PU top coat on epoxy paint (over galvanized pipe)

Epoxy based coatings chalk due to ultraviolet radiation damage, not temperature and humidity. If your galvanized pipe is exposed, use option A.  

RE: PU top coat on epoxy paint (over galvanized pipe)

Check with coating manufacturer to see if intended coat is OK with zinc plating... some are not.  You may require a primer to accommodate the zinc...

Dik

RE: PU top coat on epoxy paint (over galvanized pipe)

(OP)
Thanks @dik & @CoryPad,

What about option B with addition 100 micron of PU layer? (which means 160 micron in total). Thus the epoxy will be protected all the same.

Kind regards,
 

RE: PU top coat on epoxy paint (over galvanized pipe)

Just to throw a wrench into the mix... have you looked at polyureas?

RE: PU top coat on epoxy paint (over galvanized pipe)

Option B plus polyurethane could be considered if the primer is compatible with the galvanizing layer.

RE: PU top coat on epoxy paint (over galvanized pipe)

Not polyurethane, but, polyurea... different coating system.

Dik

RE: PU top coat on epoxy paint (over galvanized pipe)

I have seen many paint failures on galvanized surfaces. Zinc can strongly affect the chemistry of the paint curing. Every paint is a unique formulation even if it broadly falls into one category. The only way to know that a paint is compatible with a substrate is if it has been tested, and prepared the same way as it was previously tested. The paint manufacturer is the only one who can know.

RE: PU top coat on epoxy paint (over galvanized pipe)

Compositepro:

The problem with zinc is that you can have a chemical saponification, ie. 'zinc soap' that can interfere with bond.  That's the reason for my earlier caution. I, too, have seen too many failures of coatings applied to zinc...

Dik

RE: PU top coat on epoxy paint (over galvanized pipe)

(OP)
@dik,

By PU I meant polyurethane.

The way I see it, I will go for option B with addition of 50 micron polyurethane on top.

Thanks guys,
Regards,

RE: PU top coat on epoxy paint (over galvanized pipe)

I was just asking if you looked at polyureas...

Dik

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