Let me start off by saying this: If you are even considering spraying gelcoat, GO FOR IT!!! It is much easier than I ever imagined it being!!! I am no pro or expert and I just want to pass what I have learned on to others. If anyone has any additional tips to add or need to correct my methods, please do so.
I have a 1997 Champion 181 DC which needed some gelcoat repairs. I patched up several old transducer screw holes on the transom and needed to re-gel those areas. I also cut the top cap above my transom to expose the wood for drying and the application of CPES, so once that was all glassed over it needed gelcoat as well. The gelcoat work REALLY intimidated me, so I researched it on the web and got even more confused. It seemed that if I found 15 websites or posts on how to spray gelcoat I found 15 different ways of doing it!! I also got A LOT of information from a local fiberglass repair shop, which was surprising. Another local shop would not give me any tips. When asking direct questions the guy would act like he all of a sudden didn't speak English, then either mumble something under his breath or just walk away from me. And I actually spent money there, he had a close match to my poly flake. What I finally put together was the main points from all the different methods.
1. The purer your gelcoat is the better results you will get. In other words, the less additives in it the better. I heard of guys thinning with Acetone, Lacquer Thinner, MEK, Duratec (this could be a very good option and I may try it on my next project) and Styrene. I chose to thin with Styrene.
2. Spraying poly flake is either not an art like so many have claimed, or I am a true artist!!
3. Prep your area VERY good and plan ahead by prepping a larger area than you initially thought you would need.
4. Pay attention to your mixtures making sure everything is measured accurately. Also, mix every coat the same and catalyze according to the temperature (I will explain this in more detail later).
5. Gelcoat is cheaper than paint and more forgiving than paint.
6. Order twice as much clear as you think you might need when spraying poly flake.
7. Forget the "cup gun" it's a waste of money unless you are spraying gelcoat into a mold.
8. Clean your gun with acetone after each batch of gelcoat is applied. Also, don't mix up too much or over catalyze, you may run the risk of it kicking in your gun.
More to come: Equipment used.
Modified by dan-k at 1:39 PM 8/15/2011