Setup your work bench with all the essential tools and cleaners for a well planned batch of experimental spray jobs. Here’s a few things I have learned in the process of making a batches of gelcoat sprays.
Step one, get some gelcoat…
This is un-waxed gelcoat. Using this un-waxed gelcoat on the outside of a part will expose the “wet” getcoat to air, which inhibits cure. This leaves a sticky layer on the outside. Why the hell is there a feature like this? Well if you wanted to laminate or add another coat of gel/resin on top this gelcoat, you will get excellent adhesion without any sanding. This gelcoat is designed to be sprayed onto a fiberglass mold and then sandwich layered with fiberglass and resin. Or it can be sprayed in multi coat stages on a part.
On the last layer you have a few choices. You can spray your gel, then spray an air barrier of PVA wax or Pledge(seems to work). Or you can mix into your final gelcoat batch and styrene soluble wax. Polygard has something called WAX-SOL. Sometimes its called sanding aid. Polygard also sells gelcoat with wax already in the mix. Some companies call waxed gelcoat and resin Finish Coat, and un-waxed, Laminating resin.
On coloring gelcoat. There’s white, neutral, and clear and sometimes y I mean black. Black is pretty much neutral with black pigment which is what I picked up at TA Mahoney
You need to thin out the gelcoat if you want to use a siphon or gravity feed spray gun. Not too sure about pressure pot type of guns, and “cup guns” with rather large nozzles designed for spraying gelcoat need not to be thinned. Thinning agents range from Acetone, Styrene and MEK. Evercoat recommends 5% maximum addition of Acetone. Most other gelcoat brands dictate the same maximum percentage, however they recommend Styrene. This was interesting, however, not knowing, I was to follow the label. But the problem with Acetone, is that, like using wooden stir sticks, it effects the cure rate of the resin by “killing” some of the MEKP. It can make the gel very very slow to cure or even, not cure. I found this to be true as a batch I mixed with a high level of Acetone, about the max of 5%, had a lot of extra tackiness on the outer layer even with a barrier coat of wax. MEK is slow to evaporate, so its prone to cause porosity on the part.
Styrene is what gives these resins that nasty smell, as it is what is in resin and gelcoat already. So it makes sense to use this to thin gelcoat. Haven’t tried this, but the next batch is going to have some.
Get a sprayer…
This sprayer is from the good ol’ Harbor Freight. 11.99 yikes its cheap. Yea, it doesn’t spray with a damn. Im thinking about modifying the tip by drilling it out to about 2.5mm or 3/32″. The stock nozzle is 1.5mm. I think it can be enlarged as as half the diameter of the needle valve which controls the flow. I might loose some control with the enlarged nozzle. But since the gelcoat flow rate is so low as it is not a real issue if it works. I think I will try a few sizes in between stock to 3mm as to find an optimum. Most places with recommend a nozzle size no smaller than 2.0mm and I have read of 3.5 mm.
Other tips and tricks include using as much fan spray as possible which keeps the spray concentrated. Spray from 8-12 inches. And spray a coat of thickness from 15-20 mils. MEK is a good gun cleaner. Acetone is good too. Perhaps better. You can spray batch after batch with acetone flushings in between. Back flush a gun by adding acetone to the cup and holding a rag to the tip and triggering the gun.
Setups I have tried so far:
Acetone thinned 1% on the HF gravity feeder stock tip size
Acetone thinned 10% on the HF gravity feeder stock tip size
Acetone thinned 10% on the HF “touch up” siphon stock tip size
So far, no luck, all the batches so far shot too weak and thin. It took a long time to achieve a good thickness which lead to much orange peel and rough ness on the part. Im definitely going to drill out the tip of the gravity feed gun…
more to come…