Gel Coat

W

Webfoot

New Member
Tried to brush on a coat of Gel Coat, could not thin it enough. Clumped up, made a mess of all my hours of sanding.:mad: Mission Accomplished, time to go sailing.
 
Kept adding more and more acetone, no luck. Someone mentioned that the Gel Coat found in boating stores is of inferior quality. Might try using Awlgrip in the fall. Right now I'm going to call it good enough for the summer.
 
I have not? Have you? Does it work well? I am trying to get the rest of the boat finished before I deal with the rudder and centerboard.
 
Webfoot said:
Kept adding more and more acetone, no luck. Someone mentioned that the Gel Coat found in boating stores is of inferior quality. Might try using Awlgrip in the fall. Right now I'm going to call it good enough for the summer.
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What brand did you use?
I had good luck with West Marine.
 
I used West Marine with a foam brush. I may have violated the "never do it in direct sunlight" rule. Stuff cured really fast however I mixed the hardener as directed. Got to the point where I gave up and chucked what was left in the can. Really need to see someone do it successfully to figure out the technique. I went way past the 20% acetone they say to use with a Pravel sprayer.
 
Webfoot said:
Someone mentioned that the Gel Coat found in boating stores is of inferior quality.
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This sounds like your someone is Urban Mything a warning at you without knowing the whys and wherefores. Gelcoat and all resins (epoxy included) have a finite shelf life. For polyester based resins such as gelcoat it’s around 1 year for unopened containers. You want to purchase from suppliers who (A) are conscious of their stock rotation and, (B) move their resin fairly quickly. My preference is for specialty plastics (fiberglass) suppliers, boating and automotive jobbers (suppliers to boat repair yards and auto body shops), boat shops that do a regular repair business or have a good clientele base of DIY repairs. The places I’m leery of are hardware stores and big box all-in-one stores. They don’t always practice FIFO and may not move a specialty item like resin very quickly. If I open a new can and mix a test batch and don’t get the expected behavior, age of the resin is my first suspicion.

If you are mixing and working without doing a test batch … and you are working on your boat right from the get-go you are violating two golden rules and will more often than not doom yourself to a whole lot of extra work that will far outweigh time test and practice takes. Every resin batch is slightly different and your working conditions (temp & humidity) will always be different. What was good yesterday doesn’t necessarily work smoothly today … thinning needs change so does the amount of catalyst required.

NEVER USE YOUR BOAT AS YOUR PRACTICE PIECE ! … unless you really like cleaning up and re-doing things instead of sailing.


Kept adding more and more acetone, no luck.
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Did you begin with gelcoat paste (pudding consistency or thicker) or gelcoat liquid (syrup consistency)? Pre-thickened paste will never thin enough to spray, gelcoat liquid with no added fillers is what you want for a spray job, even a roll-on job. For first-timers it’s better to build up to the 0.016” to 0.020” final thickness than to try and lay it on in one coat. This takes practice… too thin and it’s prone to first year blisters, too thick and it cracks like it’s 20 years neglected in the sun.

I believe most all resin manufacturers warn not to thin with acetone beyond a certain ratio. Outside the prescribed parameters you do nothing but trash the resin’s chemistry. For high degrees of thinning I believe a styrene monomer thinner is the proper chemical to be using. For your application you need to be dealing with a specialty plastics supplier who knows the brand resin they carry and has a knowledgeable staff who can advise you on the proper thinning techniques for a successful spray application.

Some Tips:
http://www.spectrumcolor.com/technicalinfo.htm

http://www.fiberglasssupply.com/pdf/polyester/StyMon.pdf


West Marine is good, Jamestown Distributors is good. Did you read through Jamestown Distributor’s How To help section to see if there are any tips?
http://www.jamestowndistributors.com/userportal/how_tos.do
http://www.boatbuilding.net/search.pl?topic=15


What other boaters have done:
http://www.continuouswave.com/whaler/reference/whalerRepair.html
 
Webfoot said:
I used West Marine with a foam brush. I may have violated the "never do it in direct sunlight" rule. Stuff cured really fast however I mixed the hardener as directed. Got to the point where I gave up and chucked what was left in the can. Really need to see someone do it successfully to figure out the technique. I went way past the 20% acetone they say to use with a Pravel sprayer.
Click to expand...

You could use a little less hardner so it doesn't cure so fast.
I know what you mean though. It starts turning into a blob. I was applying gel coat only to patches and in cracks in the original gel coat I had widened to fix. I mixed about 1 ounce of gel coat at a time which was all I could put down before it started to "curdle" lol! My best results were using a new cup and new brush each time.
Bugs seems to think gel coat is their crack/cocaine. They kept landing in it. A few are now a permanent part of the boat since I got so tired of them. :rolleyes: I had to sand their bodies flush though. :D

If I had to do it all over again, I'd spray it on...even if it's patches. And then spray on the mold release as well. I had a lot of sanding to do afterwards, then had to go back to fill in low spots.
 
Ya, don't try to pick Mosquitos out of the gel coat, they leave a red skid mark. The good part is at least I got the patches covered mostly. The gel coat on the rest of the hull it thin enough I can sand it off later. Live and learn, I tried a bunch of stuff on this boat as a experiment. Like, always do cut-outs for your patches, never band-aid patches as the band-aid patches sit above the surface and it's a pain-in-the-butt to fill and sand over them leaving "hull warts."

Should be fun, I think this will be the first Sunfish I've sailed without water sloshing around in the hull. Last one had so much water it would plow through the water going downwind in 40 mph winds.
 
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