Noob with a noob Q...what is gel coat?

General Composites Discussions Composites Talk
#1

I have tried to ask Jeeves, I have tried to search here, but I still don’t know what the point of gel coat is? I get the feeling that it has several different uses.

1)for making a smooth reusable surface for a tool/mold
2) for building up the clear layer after a part is removed from the mold, (give that nice deep clear layer commonly seen on high end CF parts)
3) for building up an initial layer of resin in a mold onto which the CF will be layed(giving the deep clear layer as described in 2 and also to provide some sticky surface to lay the first layer of CF in complex shapes that may otherwise not like to conform to)

Please help me out with understanding this.

#2

gel coat is used like clear coat is but it is sprayed in the mold before the carbon or fiberglass is laid

#3

I see thanks for clearing that up, you are a big help in my understanding about all this stuff.

#4

thank you lol

#5

From what I have read this seems like an advanced process/technique. It sounds pretty hit and miss for beginners.

#6

Brushing on a couple of coats of gel-coat and hand laminating a simple GRP part is pretty easy.

Strangely though lots of people seem to find this very difficult, and dont seem to bother with mastering basic techniques such as this, before going attempting to vacuum infuse carbon fibre!

#7

1: Should read smooth “highly polished” reusable surface for a tool or mold.

Polishing your plug/mold saves you a ton of finish work on the finished part. And your parts will come off the molds with little effort. Otherwise some wedging/prying will be necessary.

Also if your using Gelcoat as the tool surface you would want to use “tooling gelcoat”…its way more durable than your standard gel.

#8

Thanks guy for helping him out!

It is thicker (additives) so when you spray or brush it on a surface, it stays put and doesn’t run off like lamination resin. It is for surfacing a mold (tooling grade to take many heat cycles of making many parts) or parts as most FG parts it is the color “egg shell” coating.

#9

So I would guess that brushing on a gel coat into a tool (for that nice finished look) would leave the surface a bit streaaky, while spraying would ensure a nice homogenous coat. Or is the gel coat one of those things that once brushed on it is pretty much self leveling?

#10

Shake it (while liquid state) and it will self level but if you don’t, then you will have highs and lows. That is the reason behind spraying gel coat. It levels out better but it can leave a rough texture.

But that is on the inside where any reinforcements will be added onto and the master plug surface will dictate the mold surface…

#11

If you are producing low numbers of smallish GRP parts, there is not really much need to spray gel-coat. However if you are wanting a clear surface coat for carbon, then this must be sprayed.

However most common gel-coats have additives that give them a slightly brownish tinge, so something like Duratec clear coat, applied with a spray gun is going to be best.

#12

Thanks for the replys guys. As I thought, for best results it needs to be sprayed. My master project (once I feel comfortable enough with composites) will be a whole fairing set for my bike. Obviously a nice gel coat would make the whole thing look that much better but I don’t think it is feasible for me to buy all the equipment necassary to be able to spray it. Is it possible to have a gel coat sprayed on the complete and cured part after it’s out of the mold by a professional, or to just have it clearcoated automotive style? what would be some disadvantages of this?