Painting Peel Off at Zinc Plated Part

Adhesion, or the lack of it.

Need much more detail.

It probably wasn't "pickled" first. Pickling is acid or alkaline wash depending on the type of paint.

I think this possiblility is very low, because before go for zinc plate, the part is go thru orbital process to clean up the surface dust an increase the adhesive of surface, but the peel off still happen.

Greetings.

You are absolutely right on.

We were converting a manufacturing building into our church and had these 2 foot diameter 12 foot long galvinized ventilating pipes delivered which needed to be painted.

We were told to rub down the entire surface with vinegar and then the paint would stick.

I said we are not making a salad.

The place smelled like a salad bar and the first coat stuck and covered and didn't come off.

Every trade has its tricks of the trade.

We heard horror stories of buildings that had never ending stories of paint coming off.

We were thankful that someone knew about pickling.

Have a Great Day,

Oly

That paint might be hanging on, but if you attempted to get by with just pickling, and those pipes were exposed to the elements, it would be be popping off within two weeks.

Unless you used a self priming DTM, (direct to metal), paint, galvanized metal should always be primed with an appropriate primer.

post three is truly not deserving of a 'GA' good answer here. A simple, miniscule no-effort search for information about 'pickling' will confirm that it is not recommended for galvanized surfaces.

the link given in post2 also confirms this fact.

all the advice about washing with vinegar is equally worthless. SO WHAT if it cleans off a good bit of the contaminating oxide layer??? You call that 'surface preparation'?

this is supposed to be a professional site, is it not?

unless you are a true expert, or at least have some honest to goodness experience (not just that old 'I once painted an old tin shack this way'), you should search and read a bit before offering your (so-called) 'expert advice'.

If all you are doing is "chiming in" for the sake of being sociable, begin your post with: "I once heard somebody's gran'pappy offer this advice".... and the ensuing criticism will ricochet right off of you!

Use Etch Primer on bare Galvanized surface - see post 11

I had done that in 1993-94. I did not try first paint - see it pealing off and next find solutions - Instead referred to Manufacturer of paint for suitable epoxy based paint system for Zinc surface (I had some idea that paint does not adhere to Zn, Stainless steel and Al surfaces - read in my Engineering Chemistry in First Semester of Electrical Engineering degree course - 1967).

Luckily those days we did not have google search - I am not criticising google - it is a good engine and I also refer to it often, but it has made us lethargic - that we do bother to store minimum in our brains. I am of the opinion that we should keep always basics of science and engineering in mind and then work further.

It's that simple. GA

Metal etch primer or specialized tower primer doesn't peel off and what ever goes on top of the primer sticks to it nicely.

See my Post #1 at THIS THREAD.

Searching the site for relevant topics/answers can preclude a WHOLE lotta repetition around here.

The "Warning" at the bottom of the link given by SolarE makes the "point", but does not bother to delineate the "WHY?" (for THAT particular / specific issue).

NACE (as well as others) has been teaching about "saponification" for decades now.

There exist "Coating Specifications" for most everything out there nowadays... explaining everything from 'surface profile' required, through 'surface cleanliness' requirements, through temperature/humidity allowances, etc etc etc...

"Share what you know. Learn what you don't."

Unless the part has to be painted for safety or color coding reasons, paint is redundant. The purpose of the plating is to protect more or less permanetly. The same properties that repel the elements also preclude the adhesion of most coatings. See your coating supplier for the proper procedure for using coatings non zinc.

De grease wash your plate then spray with vineger, leave for 24 Hrs wash off dry and paint.

Galvanized surface forms protective coat of Zinc Oxide which is hard and sticks to surface. This gives dull white colour to GI.

The forces of adhesion between Zinc Oxide and paint is very poor and hence it easily peals off.

To paint GI surfaces, first we apply Etch Primer in ample, cleaned, dried and painted immediately with paint to be applied. (Dry with cloth not with hot air, otherwise again layer of ZnO will be formed). This etches the Oxide layer for paint to stick.

That is how I had once pained a GI Acoustic Enclosures of 1MW DG Sets in 1993.

Best of luck

It most likely is the VOC still in primer and did not get baked completely out this usually is the cause of finish coat thinners are sensitive or not compatible with each other primer thinners.

Plated parts are not meant to be painted, however, if you do want you will need to prepare the surface properly(a light sanding to "rough up" the surface) and/or an "etching" primer can be used to "prepare" the surface prior to top coat.

Try to wash the zinc plated part with strong vinegar before painting. Wash and dry first and take the same precautions as when using strong acids