Gel Coat in making molds  
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All Forums >> RC Airplanes >> Composites Fabrication And Repair >> Gel Coat in making molds
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Gel Coat in making molds - 2/4/2004 8:45:28 PM   
yankee samurai


 

Posts: 123
Joined: 5/14/2003
From: Blackfoot, ID, USA
Status: offline 		Does anyone feel that there is an advantage of using two coats of gel coat? Adding a second coat to the plug after the initial coat and then putting the cloth and the mat on? Thoughts, would I be wasting gel coat?

_____________________________

Randy Shiosaki
       Post #: 1

RE: Gel Coat in making molds - 2/4/2004 11:06:11 PM   
Ed Smith


 

Posts: 2834
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: offline 		I have never done this. I would guess that there is a possibility the second coat might not bond to the first that well. patches of the mold surface may break away when removing parts.

Any real experiences out there?

Why do you want to do this?

Ed S

(in reply to yankee samurai)
       Post #: 2

RE: Gel Coat in making molds - 2/4/2004 11:12:45 PM   
davidfee



Posts: 691
Joined: 6/21/2003
From: San Diego, CA, USA
Status: offline 		You should only need to add a second coat if the first coat does not completely cover the plug. That is, if there are thin spots, it will be good to add a second coat. You should not let the first coat cure completely before you apply the second coat because you need to have them fully bonded together. Your surface coat should be a minumum of 1/16" thick so that the fibers of the mat and other reinforcements don't print through to the mold surface, and so you can sand and polish if you need to.

Good luck,
-David

(in reply to Ed Smith)
       Post #: 3

RE: Gel Coat in making molds - 2/5/2004 9:37:45 AM   
ColinM


 

Posts: 162
Joined: 11/7/2003
From: Cambridge, UNITED KINGDOM
Status: offline 		A friend of mine works for one of the major UK boatbuilders and when I was making my first plug and mold for my plane he came to show me how to do it. And bought all the materials "donated" by his firm with him. The first mold we took off a pretty poor plug we knew would need a lot of work, so he applied seven gelcoats to the plug so that there was sufficient thickness of gel to sand down to get a good finish. Admittedly the white gel coat he brought with him, a 25KG drum of it, was formulated for spraying so was thinner than you'd normally use. The first five coats we applied were white poly gelcoat and then the last two were black so that when sanding we'd know if we were getting close to the CSM. But the coats went on in thin layers, don't try to build the thickness up by just schlapping more on. Several thin coats are better than one thick. The whole process worked fine and when sanded and polished the mold was first class.

Other molds I've made from polyester, both white and black and any shade of gray in between, I normally use two coats of gel but color the second coat different to the first. The second coat almost guarantees that you'll get a perfect surface finish. And there are no issues surrounding bonding strength as far as I'm aware.

Oh and he tells me that full size boats normally have a minimum of five but normally seven layers of gelcoat, they aim for around 1/8th inch of gelcoat on the finished boat, firstly to get a good surface finish and secondly to give some meat to the boat to allow the owner to polish it over the years.

(in reply to davidfee)
       Post #: 4

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