# Problem w/ polyurethane top coat over spray paint



## pablopaul (Mar 24, 2012)

I am painting a shot put, as in a 6-lb iron ball for track-and-field.

I sanded off what was left of the old finish. I put on a coat of Rustoleum metal primer (spray). I put on a few coats of oil-based Rustoleum paint (spray).

The problem is the protective coating over the paint. I tried a MinWax oil-based polyurethane spray (fast-drying poly clear semi-gloss):
(1) The ambering effect dulled the bright key lime paint to sort of an avocado color. In hindsight, the label warns of this.
(2) After 24 hours, the polyurethane was tacky/gummy. I could rub it off with my thumb.

So my question is whether I need to do something different (wet sand the under coat, wet sand the poly, let it cure longer, etc.) or if I should use a different coating altogether. 
 
A shot put takes a lot of abuse – dirt, sand, mud, grass. I anticipate that I will have to repaint it every spring, and that’s fine, but I’d like to get a couple months out of the paint job. (The factory powder coating was completely worn away down to bare metal after one season.)

Ideally, I would like a coating that is (a) tough enough to take some abuse (b) without muting the bright color. However, the toughness is more important than the color. [Lime green was the athlete's idea. I couldn't talk her out of it.]


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## joecaption (Nov 30, 2011)

Powder coating is one of the longest lasting finishes you can have, it will long out live a painted finish on metal.
Poly should never have been added over the paint.
If your going to use paint then your going to have to deal with having to redo it after a few uses.


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## pablopaul (Mar 24, 2012)

Thanks for the feedback, Joecaption. As you can imagine, there isn't much out there when you Google "How to paint a shot put." So I was going with what little direction I could find.

I will look into powder coating when the paint wears off (which shouldn't be long). I wasn't impressed with the factory coating on the shot put because it wore off so quickly and completely, so I was thinking there might be some sort of poly/varnish/lacquer that would absorb the abuse.


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## chrisn (Dec 23, 2007)

pablopaul said:


> Thanks for the feedback, Joecaption. As you can imagine, there isn't much out there when you Google "How to paint a shot put." So I was going with what little direction I could find.
> 
> I will look into powder coating when the paint wears off (which shouldn't be long). I wasn't impressed with the factory coating on the shot put because it wore off so quickly and completely, so I was thinking there might be some sort of poly/varnish/lacquer that would absorb the abuse.[/quote]
> 
> ...


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## ric knows paint (Oct 26, 2011)

pablopaul said:


> I am painting a shot put, as in a 6-lb iron ball for track-and-field.
> 
> I sanded off what was left of the old finish. I put on a coat of Rustoleum metal primer (spray). I put on a few coats of oil-based Rustoleum paint (spray).
> 
> ...


Painting a shot put, eh? Not the most common discussion we've had on this forum, but I s'pose it can be done. First off, Powder Coating may have a few advantages to liquid paint, but let's not assign super-performance characteristics to a very limited application process...from a resins perspective, they are pretty much the same as liquid paints (alkyds, vinyls, epoxies, etc.), and each comes with their own inherent advantages and dis-advantages. 

...and if it were relevant to this particular thread, I'd mention that there is absolutely NOTHING wrong with putting a clear poly over a painted finish.

Your problem is the surface to be painted, and the exposure and abuse the painted item must endure. First, the steel that makes up your shot put is hard, slick and impervious. Unfortunately, this does not make an ideal surface for conventional coatings. Second, the exposure of hurling a 6 pound steel shot, onto any surface, doesn't really fit the "regular and expected" abuse a typical coating should endure.

So, you're gonna have to think more in terms of non-conventional coatings... which is no real big deal, except you're only gonna need a brushful of product to coat this thing a couple times over. These high performance, non-conventional coatings are usually found in no less than gallon quantities and often times are 2 component (parts A & B to be mixed at time of application).

A kick-a$$, bulletproof system would involve (a) Etch the shot put with acid to create a profile necessary for good mechanical adhesion...(b) prime with a high build poly-amide cure epoxy...(c) apply 1 coat of a poly amine cure epoxy tinted to Lime Green, and finally (d) apply 1 application of a moisture cure urethane for maximum impact and abrasion resistance.

Now, if you can purchase all these products, you're probably looking in the neighborhood of $200 material to paint this 6# shot put - and some may actually think that's too much effort and money, but it's still most likely to be cheaper than having it re-powdered - or buying your own powder coating gun, and oven, to do it yourself. 

...or you could just do it again like you did before, but this time etch the steel first, and realize you're gonna have to touch it up occasionally, or re-do it maybe a couple times per season...or just spray paint it lime green and figure on repainting after every track meet (thats what professional and college football equipment managers do with the players helmets after games). 

P.S. - even though I said there's nothing wrong with applying a clear poly over an alkyd coating, you really won't be gaining any advantage to doing so...so don't do it. Good luck.


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## poppameth (Oct 2, 2008)

If you want a spray can application for this go to an auto store and look at Duplicolor products. use their primer, paint and clear topcoat for a completely compatible system and make sure to follow the instructions. If you want very durable finish take the thing to Line-X and have them spray it with one of their bedliners, which are now available in several colors. I wonder if their lifetime touchup warranty covers shot puts?


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## chrisn (Dec 23, 2007)

ric knows paint said:


> Painting a shot put, eh? Not the most common discussion we've had on this forum, but I s'pose it can be done. First off, Powder Coating may have a few advantages to liquid paint, but let's not assign super-performance characteristics to a very limited application process...from a resins perspective, they are pretty much the same as liquid paints (alkyds, vinyls, epoxies, etc.), and each comes with their own inherent advantages and dis-advantages.
> 
> ...and if it were relevant to this particular thread, I'd mention that there is absolutely NOTHING wrong with putting a clear poly over a painted finish.
> 
> ...


 
Well, I am glad you added the PS:laughing::whistling2:


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## jsheridan (Jan 30, 2011)

About the PS, IN THIS CASE, the poly won't add anything. Poly does protect painted surfaces from mild usage wear and tear. This is an ongoing issue with Joecaption. I've said it before joe, and I'll say it again, poly is used in faux decorating to seal the finishes and protect them from wear, among other applications in painting for poly over paint. Why do we put poly over stained hardwood, not for the sheen alone?


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