Dépend of pigments but not to much, with liquid pigments i use it’s around 5%. Pigments are like plastizers, mechanically they reduce stiffness and increase elongation to break, at 5% it’s marginal.
It is a particle paste. It says, “The proper mixing ratio is 6-8% by weight. For easy measure, use one tablespoon of pigment per pint of resin for a dense, opaque color.”
I have been using the one Tbsp per pint recommendation without problems.
I would tare your scale and add pigment until it looks about right. Test it out on a piece of scrap cloth/foam. Write it down and then you can repeat it later. But… I guess it depends on the pigments that you use. Mine only require a small dab to produce bold colors. I try to keep it light enough so I can still see the stringer.
I do it by Eyeball. But I use Duratech pigments. So do some of the best. I have found though that it is necessary to load up Epoxy as compared to Poly. You can’t use the same amount in Epoxy that you would use in Poly. Gotta add more and a bit of white to get it to come up anything more opaque than a weak tint.
I’m an amateur when it comes to Epoxy. Lemat is an expert. Have learned a bit from reading his posts. I still have issues with sandable fill coats. If I could get that worked out I’d be happy. Too hit and miss. My biggest issue with material hardening is with “Additive F” . That stuff sets up so fast it’s not even funny. I put it in cans for resale, but it still goes solid. I got in the habit of vigorously shaking all the cans I have on the shelf every once in awhile.
I have stopped using additive F. It just doesn’t seem necessary. RR sands fine without it. When I was living up in Northern CA my Additive F would always have solids floating around in the bottom of the bottle due to the cold. You just have to give it a warm water bath before using it, and it will become clear and uniform again.
Same for me when I have real addF make with xylen. My distributor use to make is sauce with toluen… I mostly use a local epoxy brand now, after many test I come back to a bit of addF in epoxy finish coat find it slightly reduce epoxy coating problems that every epoxy users experiments here and there… But the real secret seems to be: far less problems when coating is done on an epoxy tacky layer.
I’m a bit flummoxed at the moment, as, based on what people were saying about the pigment, I went with 4% and it’s pretty blue and opaque… Now I have to come up with a plan to find my fin boxes… And, I’m worried I got to excited pulling the lam tight, as, with the sealer coat, it didn’t soak up much resin, so that was stoking… Until I realized I can’t see my fin boxes, nor my tape lines… Ha! Always something new and exciting.
If you get it that opaque, you can usually just freelap top onto bottom and it won’t show. Otherwise double or triple tape so that you can feel it. Then pull the lapped cloth up, fold it over and zip cut it. As far as fin boxes go; I always post lam the boxes and put a clear patch over.
Blue bottom lam @ 4% pigment: 3% blue, 1% white = opaque blue. Used some of the blue resin I’d already made when I sealer coated the deck - it was real blue like the bottom - so I did a 2% white, thinking (Hoping… Ha!) it’d be translucent, and create a light blue… Ha! Not!
I’m thinking of a .5% blue tint for the filler coat on the deck and a .5% white tint for the bottom…
Deck belly for paddle, parallel rails for speed, hull/belly in nose to mid/to (hard to see) double concave w/significant vee through the fins to flat panels behind rear fins.