Tips for spaying gel coat (Overlay)

General Composites Discussions Composites Talk
#1

Generally if I spray gel coat it goes in a mold. I did some overlays (under vacuum) and wanted to spray them with clear gel. I have a gravity feed HVPL gun (2.5mm tip), PE Clear Gel and Duratec high gloss additive.

I sprayed it once already. Got a lot of orange peel. I think my pressure was to high. Wet sanded to 400. Now I’m looking for the best method for a good wet on wet build and minimal surface finishing.

Would a small amount of thinner or reducer work. Thinking that once the first coat flashes I could add another…

Looking for directed to speed the learning curve :wink:
Jeff

#2

Unless it’s meant for topcoating, you just won’t get good results. Gelcoat is not meant for this.
Use a Duratec clear topcoat, or an automitve clear. They are thin, flow nicely to level the surface, and dry to a hard finish.

#3

I believe the Duratec additive is made for top coating. I know it’s an air cure and uv protectant. Maybe I’ll just have to shoot it again under lower pressure/more additive and see, wet-sand if needed. The fibers are still translating through. I don’t think an automotive clear has enough build to cover that.

I guess this is one of those cases where you learn what not to do. :smiley:

#4

PER clear gel coat is the problem… gel coat is meant to always have a lumpy ( orangepeely) surface. This is because gel coat is made to be sprayed into a mold then the fiberglass or carbon fiber covers the lumps.

Try spraying just Duratec clear ( not the same as gel coat). You may be able to add some of that gloss addative to the Duratec clear.

You can do what you are doing, spray on 30 mils or so of clear gel then blocksand it down smooth starting with 100 grit. It is a lot of excess work.

Polyurethane clear paint (2K automotive stuff) is the easiest thing to clearcoat over an overlay or part. Like TET stated it self levels with minimal orange peel if any at all. Also the nice thing is not only with enough coats will it fill in the weave level, but it is also a UV protectant.

…and if you already knew this… sorry :stuck_out_tongue: :cool:

#5

If you ever want a cheap and fast way to coat and seal the overlay carbon fiber, use polyester or vinylester resin. It will be lumpy as heck after applied, but you can then sand it smooth up to 400 grit wet. Then spray on your clearcoat. VER and PER sand more easily than gel coat does.

One disadvantage to using VER or PER is it is not 100% clear, but over carbon fiber it is not too noticeable.

#6

PER coating can be done by thinning it somewhat with styrene and pouring it over the object. Then shake it some to level the layer out. Might help to bolt a vibration sander to a table to shake it.

Or I have used thrift shop electric shavers to do that too…:wink:

#7

Duratec makes two different products. A clear coat (thin viscosity) and a Clear Additive. The clear additive can be mixed with clear gel coat (minimum of 30% additive to 70% gel coat) to get UV and air cure.

I never used the clear coat myself. I usually will spray with an automotive clear for a top coat like that.

I experimented this weekend and got a very good result I would like to share. I mixed the Duratec Clear Additive 50-50 with clear gel coat. I mixed both well and added 2% Mekp. I then added 1% reducer. I spayed at 20psi first with a thin flash coat and 6-8 wet coats (let flash for 5-7min between). The material laid very nice, thick and smooth. I got a very slight ripple after cure but it I think it will polish out easily.

I would like to try with some flattening agent also.

#8

Very good.
By the chance, do you have any pictures??