Pin-holing in gelcoat

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#1

I was with a company yesterday who were having problems with air bubbles on gel coat surface and bubbles just behind the gel-coat surface that are very easy to crack. The gel-coat is sprayed on and then a chopped strand is hand laminated on the back. The problems experienced are all bits that need fine tuning just as opposed to major errors (in my opinion!)

The gelcoat is, by nature, reasonably viscous. It is poured out of a huge tank into buckets, causing air bubbles from the flow. The agitation and mixing takes place with an air powered drill with a propeller on the bottom, similar to this:
http://image.made-in-china.com/2f0j00kvbtoZAzfqcp/Electric-Drill-Mixer-.jpg
For production reasons, this gun is obviously turned up full speed! Now there are plenty of air bubbles in the mix (about 4 litres in total)! Then, the mixture is passed to a cup, inserted into the spray gun and sprayed.
I don’t have much experience in spraying but Im guessing a lot of pin-holing is also induced during this process: from shaking the spray gun as opposed to being smooth but also from a machine gun like effect on the spray gun itself.

So, we’re trying to reduce air bubbles. The mixing alone has probably the most profound effect, so, when mixing, what is the industry standard for mixing and agitating larger quantities of gel-coat?

Thanks v much as always

#2

Do you have any type of inline or Desiccant Dryer Filter on your spray gun? If you are applying it using a brush instead of a gun, there not to much you can do.

#3

It might be worth the investment in a proper gel spraying set up, you can get some small ones now. These have a suction hose that goes directly into the gel keg and a seperate catalyst reservoir. The two parts are then mixed either inside the spraygun tip or just outside the tip with atomization so no stiring. I have only used the intip type which gave good results and a good move up from the cup gun that was used prior.

#4

No, nothing overly fancy on the guns that Im aware of anyway. Have you any idea where to start looking for the atomisation spray guns, other than the usual google searches? certainly sound interesting
Thanks v much