I’m wondering if this is possible, what would I add. I am looking to use something as an epoxy surface coat (in stead of gelcoat) and I have some of the jgreer 300/21 epoxy on hand. Would adding talc until I get the consistency I like be a suitable method? would it be possible to sand and buff this cured surface? or would I suffer from lots of porosity due to the filler?
you can use cabosil to make the resin thixotropic. obviously it won’t be a clear surface coat but if thats of no concern then you’re good to go
in my opinion you should just buy a surface coat. its not worth having a mold come out bad, and when you do the math it really isnt to expensive per mold/part. check out huntsman 8026 aluminium filled epoxy surface coat, you can get from northern fiberglass for a reasonable price
I make my own, comes out good. 4oz of resin to 4 tablespoons of calcium carbonate, mix thorougly then tint with epoxy dye by 3%.
jgreer also sells pint size liquid epoxy dyes. Black, yellow, blue, orange, red, green. $12 for one pint.
The thing is that I’m planning on using it for tooling surfaces as a surface epoxy coating, I’m worried about porosity as a result of the filler. Have you experienced any issues in this regard?
I find that the 300/21 jgreer stuff is just a bit too thin to get a surface coat that I feel comfortable enough with it’s thickness, especially on vertical surfaces.
Hojo, would the semiperm sealer aide as far as taking care of the potential problem of porosity? I know I might as well just buy some proper epoxy for the job.
yes, sealing will help alot for any mold, and I highly rcommend sealing any mold new or old. Iam going to try a new sealer soon from huntsman, when I do I will tell you how well it works. its a little expensive, but from what I hear its well worth the price…
p.s. make sure you close up your freekote very well after using it, otherwise it will not last long and you could stick a part. and always do a tape test before lamination
what is a tape test?
try graphite powder along with cabosil as well. Make sure you degass it well.
a tape test is when you take a piece of 3/4" masking tape, stick it to your index finger, and stick the other end on to the mold surface well.if you peel the masking tape up with out it sticking the surface has sufficient release on it. if it wants to stick then it does not, and will require another coat. you will be able to tell the difference between a well coated surface vs. a poor coated surface
I see thanks.
These would add hardness and heat transfer would they not? wouldn’t it become harder to sand and polish the surface?
tooling surface coats are best to be very hard
it isn’t as easy to sand as gelcoat but you can sand and polish without problems. The graphite helps in make a really hard slippery surface. I actually prefer my epoxy molds made this way to the ones I have made using real epoxy surface coats. Epoxy molds also should be vacuum bagged.
may not be what you are looking for but i have added glycerin to gellcoat it will thicken it but will take 2-3 days
RC51, maybe try the jgreer 300 resin with the #11 hardener…i think it’s much thicker. I should switch myself to the #11. I need to place an order to him soon, so i’ll buy it when i do.
Graphite powder… my main concern is the mold surface turning black and having a negative effect on the epoxy dye, overwhelming the yellow or orange turning it black.
You can also add aluminum powder made for making epoxy surface coats. I have seen it for around $30 a quart, but it should last a long time.
With making my own epoxy surface coat…no air bubbles AT ALL, WAY better than PER tooling gel coat as far as air bubbles are concerned. However i have noticed PER tooling gel coat is harder than my stuff. Another thing that can be fixed with a ratio correction on my stuff… i was adding too much marble powder (calcium carbonate) creating a more “chalky” coat once cured. I buy my calcium carbonate from PolymerProducts on ebay… they grind it superfine so it’s not chunky or clumpy at all, plus they put it thru more processing than other company’s calcium carbonates.
I’ll give graphite powder a try.
do you degas to make sure that there are no bubbles? how is it that you never get bubbles if you have to mix the resin/hardener and then add the fillers? just using epoxy that has been degassed I really have to be careful not to incorporate bubbles as I brush the stuff on…
I’m not really too worried about the color thign with graphite, all my molds are actually clear, I like to be ablt to see through them. I can see the progression of the infusion form the bagging side and the mold side, plus see any potential bubble problems. Plus I never do any gelcoating in my molds so I really don’t need any visual aides to judge thickness of gelcoats…
If you mix the fillers in to the resin part first you will need to adjust your mixing ratio up slightly, weigh it before and after to determine how much more hardener you will need. if you mix the fillers in after you mix your resin just make sure you have enough time to degas it and apply it. with any really thick epoxy surface coat it is usually best to apply it with a squeegie instead of a brush, but if it is thinner a brush or roller will work well to. just make sure the surface is not too thick. if your making a epoxy mold you will need to vacuum bag your laminate. if youy dont you will have alot of air and voids which when you start post curing the mold will cause serious problems
I mix the resin and hardener first, then add the other ingredients. RC51, I’m not sure why i don’t get air bubbles in my epoxy surface coat, when i brush it on there are a zillion air bubbles, then on their own they escape and i end up with a perfectly smooth surface coat. My only problem is the jgreer #21 hardener is too water like in viscocity… i need a slightly thicker hardener. The #11 is a 1:1 ratio with the #300 resin.
If you find an epoxy you like better for mold surface coats, be sure to let me know 
what you need to be worried about is purosity, you will not know you have it unless you use a microscope.any surface will have it, some worse then others, usually it doesnt get too bad untill you start sanding and buffing your mold. thats why it is important to degas your surface coat before applying it to your mold surface, and sealing it 4 times after you finish your mold, before adding a release agent
I don’t degass the surface coat mix… brushing it on causes tiny air bubbles, and as we all know you don’t spray epoxy.
What i want is a surface coat, when in it’s liquid state, is thick so it will cling to vertical surfaces without running off. Also i quicker gel time would be nice compared to the epoxy i use that has a 30 minute pot life. I’d like to find a thick epoxy that has a 12-15 minute pot life.