Newbie, help as usual please, resin selection and silicone Q

hello everyone, first post on this board, i’m hoping I’m in the right place because I’m not sure what the premise of this group is, but i’ve searched and searched and this is the closest message board i could find to what i’m doing.

  1. I’ve been making molds for motorcycle parts for the last 9 months using an epoxy resin. The only drawback was the time it took to dry. I could usually only get one part of a multipart mold done in one day. Since we got a new person, he recommended using Polyester, which i had thought of, but didn’t have any experience using polyester to make molds, I was unfamiliar with the perfect mix ratios and good layup technique to work with a fast drying resin.

Since we now have a good laminator I don’t mind using the polyester except that it shrinks. I’ve never had this problem with the epoxy, using an adtech surfact coat 7:1, and a laminating epoxy resin 2:1.

What I would like of course as everyone i’m sure, is a resin that dries fast and doesn’t shrink. i would prefer it to be epoxy because I don’t like the poly fumes, but hey, i’ll just buy some different filters for the mask if i have to, and also, i prefer to use the epoxy surface coat as opposed to the poly tooling coat as well.

any suggestions for what I need. I thought about switching to a faster drying epoxy, but I don’t know where to start other than “faster drying epoxy”.

  1. I’m using a silicone, (I’m looking for a part # and description from the vendor) to make some of the more difficult parts, to eleminate alot of work for me, and alot of work for production. the problem i need to eliminate is how to get the silicone to adhere to the resin. OR… if i can use a different flexible, affordable molding material instead of silicone that will adhere to the resin.

Urethane resins are VERY similar to silicone. except that they stick to other resins. (except for silicone).

Silicone also sticks to harder hrades of silicone. (inquire about it at your supplier)

Did you think of holes to mechanicaly hold your silicone in place?

Just 3 suggestions of a recent grad.
Hope it helps.

great ressource (from the materials section of core77): the a to z of materials… it really is.

Of course… a mechanical bond… silly me.

and thanks for that website, that’s the kind of info i’ve been searching for, although, there is a lot of it. I’ll have to spend alot of time i think sifting through it to find what’s useful to me.


You might also try a castable Urethane rubber, rather than a silicone, since urethane has a higher propensity to bond to other cast plastics. Smooth On has a huge selection of castable rubbers:

So many in fact, that it’s probably a good idea to E-Mail, or call one of their customer service reps. They’re not so bad - they talked to me when I was a student which is more than most places will do.

Make sure you get the “dry” urethane. The wet one is oil impregnated for making concrete molds.