good day! is it possible to make a mold by just using fiberglass and polyester resin without gelcoat? i’ll just smooth the surface out with bodyfiller. 
I’ve tried it to save money but the mold ended up leaking like crazy. From now on I’ll just use the gel coat to be sure the mold will work.
thanks for your response. i was also thinking the same…to save money :o. do i have to make the part to be molded as perfect as possible before applying gelcoat or i could just make repairs on the gelcoat using body filler to smoothen rough areas?
Its usually easier to perfect the plug than fix blemishes in the mold. You can make your own surface coat by added filler to your laminating resin. I use West Systems 404 High Density filler and graphite powder. This works well with my techniques. I put all my time into the plug and the mold replicates the plug finish so no polishing is necessary.
^ What he said… Hit the nail right on the head…
^ What he said…hehehe…You will save money if you make the mold right from the begining using GelCoat.
Here is a little video that I made eons ago about making your own mold surface coat. I now use graphite instead of the black tint. My present combination is 26% West Systems 404 and 10% Graphite Powder by weight.
I don’t know if your mold is for hobby use or for higher production but taking the time to get quality surfaces will save you both time and money in the long run.
Saving money by skipping the most important part of a mould? It is the same as saving dollars by not adding an engine in a car.
I oncce brushed on six coats of tooling resin over the plug in place of gel coat. It worked… But the mold didnt last long.
High temp carbon moulds for autoclave curing are made from carbon prepreg without gelcoat, but they do not have a perfect shiny surface.
Mix the gelcoat by yourself, take some resin and mix it with the color pigments you want, aluminium or glass powder and some thixo( aerosil). Is quit cheap for smaller amounts and works fine.
thanks for the responses guys!