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Good write up..

no photos tonight but i will update the thread

my boat is an 83 hunter, and with its age it needs some paint. but before i paint i will be fixing all my gel coat cracks. the procedure i am using is to open the cracks up using my dremel, then filling them with filler.

first step is to get a decent cutter for the dremel, make sure to get a carbide one, as high speed steel ones wont last long on fiber glass. if you just have a few you can just scrape them with a screw driver, but the dremel is much faster. remember be careful with water and electric. then just follow the crack with the dremel on about medium speed, just like you where drawing on them with a pencil. this should open them nicely for filling and relieve the stress in the gelcoat. after the dremeling i wipe the crack with alcohol to remove any wax. i like the dremel because if there is any separation of the gelcoat from the glass underneath you can hear it.

okay i dont like using any thickener in gel coat because i believe the thickener can allow water into the glass under the gel coat. so the first coat i do is straight non sag gel coat from west marine, it is a finishing one so it will cure on its own. i just mix some up and spread it with a spreader, it is thin, and will run contrary to what the name of it says. all we need here is basicly a sealing coat, and to start the filling steps. once the first coat is cured, wipe it down with more alky, then lightly sand any surface build up off. the next coat i do it the same gel coat with some fairing thickener in it, the west system stuff is brown so it stands out some. when applying it i also just use a spreader but i gently spread it, so it lays over the surface and fills the ground out area. once it cures i go back and sand it with 150 grit paper, using blocks, fingers what every is needed to smooth it out. the thickener will make it easy to sand.

some will say to use epoxy for this and you can, but i like the gel coat because will cure faster and you can do several steps quickly. if you plan it right you can dremel out one area, fill it, then dremel another while the gel coat cures. then fill the second and while it cures sand the first.

final step before painting for me is to get a sponge roller and roll on a thin sealing coat of straight gel coat. after the sealing coat cures give it a light sanding after the alky wipe with 220 to feather the edges and smooth it out. if you are not painting give it a few more coats of gel coat working each out over a slightly larger area, one inch larger each coat is good, sanding each lightly after an alky wipe. when its nicely coated give it a sanding and polish to your hearts content

i will post some pics in a few days
Two things that may help.

1) Contrary to popular belief alcohol or denatured alcohol are not good dewaxers. Finishing gelcoat is loaded with liquid paraffin. Use a good solvent designed for dewaxing like Interlux 202 or Pettit 95 and multiple rags. The solvents remelt the paraffin and the rag carries it away. You can easily redeposit the paraffin by not turning the rag or not using new ones often enough.

2) The secret to thickening gelcoat is Cabosil or coloidal silica. It is white, will not bleed through and works wonderfully for this task. I would avoid microbaloons for this..

3) New gelcoat will cure harder than the old is. It is not a good ide to try and sand the new flush with the old. A better method is to take it down with razor blades, jewlers files or sharp chisels until just about as flush as you can get it. At this point you can wet sand. Sanding the entire surface flush can result in thin spots in the old gelcoat.
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