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"Second" / Top coat peeling - Powder over Powder

November 2, 2009

Hello All,

I am in a bit of a dilemma, and would appreciate any and all support with this.

We are a Powder coater that handles some really large parts, some 50 ft long weighing in at 5000 lbs. to small stuff.

Most of the projects are flawless as can be (without further nitpicking) some on the other hand give us a run for our money

Problem:

For the most part, the projects are flawless as can be (without further nitpicking).

The issues arise when we are coating larger pieces (mainly poles) where the powder tends to stay "frosty" in the heavier metal areas.

This forces a second coat for aesthetic purposes. What we notice is, the top coat tends to peel or not adhere well.

Observatory remarks:

The "frosty" look is due to part not spending enough time in the oven and not flowing more.

The second coat can be applied with more prep on the parts along with sanding and such.

Pre-heating helps, but only so much.

Question:

Is there anything in the coating itself that would hinder this even more?

Is there any other way to prep the part?

My sincere apologies if this is confusing, just looking to see if it's possible to re-coat an already coated part and attain a good adhesion.

Ritchie Desai
Manager - Cleveland, Ohio

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November 6, 2009

Your question brings to mind a letter that an enthusiastic house owner sent to a well known DIY magazine it went:
Dear Sirs,
I am seeking your guidance on a problem I have in building a three foot wall on my property. To start, my son and I dug a trench and in-filled it with concrete. This was allowed to dry-out for a few days. We chose an early start and nice day to carry out building the wall. With a short break for lunch and tea, we had completed the task just as it was getting dark. The family retired to bed happy in the knowledge we had carried out the task to everyone's satisfaction.
Naturally, we arose at the crack of dawn to inspect our efforts of the previous day. It was with great sorrow and disbelief at the scene that lay before our eyes during the night the wall had either fallen or was pushed over by local vandals? However, determined not to be beaten by this set-back we gathered all the bricks together and started all over again to re-build the wall. It was decided that this time we would attempt to increase the height of the wall to six feet and in-additionĠ to improve our method of construction, it was agreed that when laying the bricks in the upper portion of the wall (the last 3 foot) we would add some cement to the sand and water mix we were using on the lower levels.
My question is: If I applied a coat of anti-vandal paint all over the wall would this prevent the wall falling over?
I await your early response
A.N Other (Mr)
I think your problem is very similar to the above? I believe that in trying to overcome an initial problem (under-cured powder) by applying a second coat and is not the correct route to take. I would seek an answer to fully curing the first coat, By applying a second coat to improve the aesthetic value of the final finish is time consuming and an additional cost that could be otherwise used to improve the baking cycle of the first coat.
However, once this is achieved and you wish to apply a second coat of powder then you have two options:
1)Apply the second coat of powder to the item before it cools to room temperature following the first baking procedure. A second baking will be required.
2)Onto a powder film that has been fully cured but has cooled down to room temperature apply a waterborne primer (contact me for details) allow this to air-dry, apply and then fully cure the second coat of powder.
You should obtain the help of your current powder supplier to ascertain if they have a faster cure powder.

Terry Hickling
Birmingham, United Kingdom