Wayne:
The thinned gel coat can be sprayed through an HVLP gun.
Couple of things to remember.....you have to use about 5 times as much MEKP (catalyst) as you would normally with just gel coat alone.

You don't have all the time in the world to shoot it, and the gun has to be thoroughly cleaned immediately, for obvious reasons. I don't use gel coat with wax in it, but you DO have to spray a coat of PVA on the gel coat after you put it on your plug.

You know that it cures in the absence of air, so it has to be sealed (which is what the wax would do if it was in there) and the PVA does that just fine. If you don't put the PVA coat on after the last coat of gel, it's not going to cure and will remain a gooey mess.

After putting the PVA on and letting it kick, (I usually give it at least overnight), you can start sanding.....if it went on pretty smooth you can start with #400 and work up to as fine/smooth as you want the surface to be. I usually go up to at least #800, but have gone as much as #1500.

The plug surface is going to determine your mold pulling surface, at least the start of it.

When you get finished sanding, then you start buffing. I usually go 3 stages up to machine glaze finishing compound. There are many products out there that will do the same thing, but I generally use McGuires. You can order specific mold polishing compound from most fiberglass supply houses too. Buffing can be an "art". The method I use combines the compound with clean water, never let your surface get "dry"...when you get to the point you're almost done, you're using mostly just water....and a GOOD buffing pad. I like wool, but I'm old school, I guess. There are foam pads now, that will pretty much do the same job, but to me, they are harder to use. I guess it's a matter of what you're used to.


The same process is followed on the mold pulling surface, (I use tooling gel coat, and I'd think you should too...it withstands much higher curing temps, that you encounter when parts you put IN the mold are kicking..), i.e., sand, sand, sand, buff, buff, buff.

Also, I generally do the orange (or black) tooling gel coat as the pulling surface, after building that up sufficiently, (15 -20 mils), I put a "tracer" coat of white gel coat on about half that thick, but only because that's the way I was taught to do it. If you ever sand through to the tracer coat, you know you might be making a new mold soon, or doing some mold repair!

Anyway, there's lots of vids out there walking you through mold making, everybody has their own little "tricks" they like to use, and you can always look the process up on some of the supply house sites, like Fiberglast.com...their stuff is expensive, but they do have more than a few tutorials and lots of info on doing all sorts of composite work, including mold making.

So, there's another cent and a half worth of trivia. Hope some of it helps you a little.

You might just be ok with your original plan using the polyurethane single stage. Its mostly a matter of creating an effective barrier coat between the plug and the mold. Parting wax is what I count on 99% of the time and it generally works, but when MAKING a mold, or using a new mold (less than 10 pulls) I will also use the PVA, or Fibrelease, usually PVA. Some of the old timers used to use Johnson's Floor Wax and it worked too!

Doing the gel coat finish is very labor intensive and time consuming....and you are doing an entire body! You might be another year just prepping to lay the mold up!LOL I think I'd probably figure out a way to use the paint! You have to basically do the same process with the Duratec, but it IS cheaper than gel coat, but not by a lot.Duratec

Given the caliber of your work on this project, there's no doubt you will produce stellar molds, which will produce stellar parts!

Keep the updates coming.

HAGO!

P.S. Don't forget the 10 coats of wax on the plug, after the sanding/buffing, before the PVA.

Same thing on the mold before using it for the first time.....and oh yea....it should probably cure for at least 10 days or so.

Not "Hard and Fast" rules, but ones that I've always followed with good results.

[This message has been edited by Sage (edited 03-02-2020).]

First off Saga , thank you for all the great info.... I've printed off your suggestions and instructions to have on hand as I go forward.
I'm going to start cleaning up the shop blowing everything down to help remove all the dust that has been produced over that last few months in preparation for painting.
I got the single stage urethan paint today along with the harder and reducer , I'm hoping to start painting in the next week or two.

I have been busy working on the car, I have been doing a few chores needed around the property.
I installed a 12" x 20' x8' garage in a box to give me some more room as I go forward , the weather is getting better !




I also have been finishing off the underside of the hood getting the it ready grinding down all the sharp edges and closing off the openings to make the mold. Its a pretty complicated design but it will mold fine.




More to come
Wayne

[This message has been edited by dobie1 (edited 03-09-2020).]

Well I hope everyone is safe and not infected with Covid 19.
I have been in isolation working on the build, Luckily I am retired so no real reason to leave our home other than for food.
I have been busy I've taken all the panels off the car and finished them all individually and then remount each piece to ensure they all fit perfectly, very time consuming.
My hope is by taking these extra final steps before painting , the parts I produce will fit Exactly as the originals.
There was a lot more sanding and finishing than I thought was needed. But when your going to make molds its has to be close to perfect, what ever isn't perfect will end up in the parts.
Here are a few shots of the door panels and one of the fender running boards.




The weather is still bit cool so it is taking a bit longer for the parts to dry, so it will be a few days to get everything done.

Thanks for looking and please be safe and social distance in these times.
Wayne

[This message has been edited by dobie1 (edited 03-27-2020).]

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86 GT built 2.2 ecotec turbo
rear SLA suspension
QA1 coilovers on tube arms

[This message has been edited by RCR (edited 03-28-2020).]