View Single Post
Old 06-11-2015, 02:54 PM
Admirals ClubCaptains Club Member Admiral's Club Member
THT sponsor
Join Date: Jul 2005
Location: Miami Fl / Washington NC
Posts: 2,017

Originally Posted by JoseG View Post
How is the gelcoat applied for boats to come out of the mold already gelcoated? is it sprayed on the mold before laying the fiber glass?
Yes that is correct.

There are two classes of gel coat. Exterior and Interior.

The exterior is used in a mold first. It has what is called an air inhibited cure, Gelcoat iis 35-50% styrene, When the mold is coated, the styrene on the surface evaporates and is not available to link with the rest of the resin in the gel coat so the surface cure is inhibited.
Adding a laminating resin on top of the gel coat replaces the styrene and you get a chemical bond between laminating resin to gel coat.

Interior gelcoat has a wax additive which floats to the surface, prevents the evaporation, and allows the gelcoat to cure completely. This is the gel coat used as a coating, such as in the bilges.

Exterior gel coat can be used outside of a mold by mixing in a wax additive yourself that comes to the surface and seals the gel coat from the air.
You can also spray a coating of PVA (poly vinyl alcohol), which is a thin liquid mold release and it makes a film that does the same thing as the wax.

You don't want to get the two confused. :-)

Last edited by Otseg; 06-12-2015 at 01:14 PM.
Otseg is offline