I recently had an e mail from an On Board reader wanting to know a little about gel coat and how to apply it. Gel Coat is basically a polyester resin that is applied to the inside of the mould onto which subsequent layers of fiberglass mat and resin are added to the required thickness thus building up the hull or other fiberglass part. Gel coat is the part that gives the boat or other moulding the nice shiny finish when it is released from the mould.
The clue is in the name gel coat and for it to cure properly it needs to be sealed off from the outside air. Gel coat if applied to a surface and not covered with another material will remain tacky to the touch, but when used as the external surface of a boat will cure as one side is against the mould and the other is covered with fiberglass and thus both surfaces are sealed from the atmosphere. This explains why when doing a gel coat repair to a boats topsides, (nick,dings and scrapes) it is necessary to cover the surface of the freshly applied gel coat with some plastic or tape; saran wrap is a good choice. With the air thus excluded the gel coat will harden under the tape or saran wrap which can then be removed allowing the resultant surface to be sanded, buffed and waxed to match the surrounding original surface.
One way around covering the surface to promote curing is to use a waxed gel coat. The wax rises to the surface and excludes the air thus allowing the gel coat to cure. This product is great way for an owner to coat the insides of lockers, under engines and other areas that may be raw fiberglass which would be otherwise hard to clean. The product shown above works a treat for this but you have to be careful not to try and put too much on at once or it will run and sag, also it has to be applied to a clean dry surface and finally if using more than one coat requires wet sanding between coats both to provide some bite and to remove the wax on the surface. Of course you do not have to use pre waxed gel coat at all you can just buy regular gel coat then before mixing in the catalyst drop in some wax which is stirred in with a suitable stick. The ratio of wax to gel coat should be in the range of 2% by volume but I have found that dripping in a few drops of candle wax from a melted candle is sufficient for a dixie cup full of gel coat and works a treat.
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