Questions about Gelcoat

General Composites Discussions Products Talk
#1

i lurk the forums quite often but have never really posted. im having a problem with one of my pieces and it seems this may be the solution. i dont use gelcoat so ive read up on it but there are a couple questions that i still have.

1.) is it really that necessary? meaning, will i always produce a better product when using a gelcoat on the mold.

2.) does it have to be sprayed on? i currently dont have a gun and would like to dodge buying one as i dont do many projects.

3.) you put it on the mold before laying the reinforcement. after extracting from the mold, do you put it on the product again? as a layer of finish?

any comments would be appreciated.

~Eric

#2

1.) No its not necessary. It depends on what your definition of “better product” is. If you are making cosmetic carbon pieces, gelcoat is a good idea unless you prefer the flat look. For anything that will be sanded and painted, gelcoat is a must. Gelcoat will also protect your mold from abrasion while laying down fabric.

2.)No, PER does not have to be sprayed on. You can brush it on, but you have to make sure you put it on evenly. Any large brush marks/puddles will distort the carbon when you lay it down. Epoxy can never be sprayed.

3.)Not more gelcoat. Most people either use duratec top coat or an automotive polyurethane clear for UV protection.

#3

Think of it this way, Gel coat (or epoxy surface coat) is like the shell of an Egg! Without it, you have lots of extra post part making finishing.

With a composite part, it is the finish side that is laid first in a mold!

#4

thank you both for your responses.

werksberg said epoxy surface coat. now i have a sanding aid that was including with my silmar 249 polyester surfboard resin. would laying down a coat of the resin with the sanding aid be the same? i was told that the sanding aid needs to go down last on a finished product for the final resin layer. this sounds a lot like a gelcoat.

i appreciate the responses, keep them coming!

~Eric

#5

Epoxy surface coat = epoxy gelcoat. Epoxy “gelcoats” are called surface coats.

If you do not use the sanding aid, the top layer of resin will remain tacky. The tackiness is there to allow the next layer of resin to chemically bond. The sanding aid is used to let the last layer of resin fully cure.

If you are doing an overlay, gelcoat is not required as it is to thick to self level.

#6

In my experience you can brush gelcoat, but it’s definitely tricky and you definitely need a good brush and good technique.

The hard part is that you abolutely must brush the entire surface from one side to the other and NEVER go back to “touch up” a spot. Do the whole surface, let it cure well, then do another whole coat if necessary.

It’s really hard to resist going back tp try to “fix” spots. It’s more like “spreading” than “painting” I guess…

#7

Also, if it is a small mold, shake it after gel coating to smooth the gel coat layer out more.

If not, brushing leaves many ridges (mountians) and valleys which can lead to weak air pockets in your gel coat surface after the part is made or in your customers hands…

#8

well, i just popped a second part out without gelcoat and it seems to be holding up okay. im compressing the c/f between the original part and the mold using c clamps and it seems to be coming out great. the next step ill be taking is another layer of the surfboard resin but this time with the sanding aid. compress between the two layers again, sand lightly, clearcoat, sand lightly, and wax. any tips or redirections? with these small pieces, it doesnt look like i need the gelcoat.

~Eric

#9

Surfboard (or sanding) PER resin already has the sanding aid (liquid wax) in them. The idea is that after laying the Surfboard / sanding resin down, the wax comes to the top to seal off the air and allow full cure that isn’t sticky so you can sand it.

#10

when i bought the resin, i received a bottle of mekp and a bottle of their sanding aid. it did seem quite easy to sand with just the mekp though.

~Eric