Epoxy resin and Silicone Rubber mold help

[Ikaros]

I'm not sure were I should be asking this question.

I need some help/advice on a project I'm working on.

I made a silicone rubber mold and what I need to do now is apply epoxy resin (with hardener) to the silicone rubber so I can have a negative (shell). But i'm concerned that the epoxy resin will stick to the silicone rubber and I will be unable to remove it after .

What do I need to do so this doesn't happen ?

[Mad Welder]

As a hobbist, I have made several silicone rubber moulds but never used epoxy resin in the construction of the finished product only polyester resin for some end products but no removal issues i normally use a releasing agent even when some manufacturers suggest not needed. Also when making Polyurethane end products still no adhesion issues when seperating from the silicone rubber mould.

Apparently the silicone has a particular oily finished surface after correct mixing (essential) and curing time and this acts as a release agent. however if the mixing isn't correctly weighed and mixed you will have curing and sticking issues, but as with anything the only advice I'd suggest is practice on a few odd shaped objects before your actual project.

I have never had an issue with silicone rubber adhering to anything ha ha and even after an accident and dropped the liquidified solution of rubber I just wait for the required curing time and literally pull the rubber off any surface. depending on the product used and manufacturers specs approx 15 hrs but again depends on product thickness.

When creating timber plugs, I have also used MACWAX and HONNEYWAX for some of the more porous timber surfaces as a release agent, as some of the more porous surfaces can cause adhesion of the silicone rubber.

A suggestion for info is MB Fibreglass supplies online UK & Ireland - mbfg.co.uk, I have not connection to the company ha but for me in Ireland they're on my side of the Atlantic, I have purchased a lot of stuff from them in the past and used them for information only too, by accessing their free MSDS in pdf, ha don't expect an immediate response to an email question but an online order/purchase is delivered promtly.

Additionally a youtube search of Silicone Rubber Moulds or DIY Silicone Rubber Moulding will reveal some interesting videos and facts as a picture will express a thousand words...!

One last bit of advice the curing of epoxy as with some of the polyesters creates heat through the exothermic reaction while curing and this heat can and WILL distort the shape of the curing casting depending on its thickness respectively will increase the heat, this can be resolved by either cooling the mould prior to the poring of the epoxy but not fast cooling when the casting is in the rubber mould ie submersion in water as cooling too fast will alter the mechanical properties of the epoxy casting causing a brittle or fractured product. What I have done to overcome this with very good results is to form my silicone moulds in a box, cylinder or casing to reduce the expansion/distortion from exothermic heat.

Good luck with your project.

[Ikaros]

Thank you very much for your detailed reply.

I checked out some youtube video's and saw/read somewere that Saran Wrap was used on the silicone rubber to protect it from whatever was being applied.

I used a similar method before with garbage bags (believe it or not) but it worked, crude though. The epoxy resin never stuck to the garbage bag plastic, when the epoxy dried, I was easily able to peel off the garbage bag with no problems.

I was considering to use this method again but it will be hard to work with. The silicone rubber mold is small and using a garbage bag ( cut down to size of course ) will still be tricky because it will be very loose and won't stay on tight and in the shape of the mold.

So "Saran Wrap" might do the trick.

Again, thanks for the response, I'll consider everything you said.

[Mad Welder]

The silicone rubber mold is small and using a garbage bag ( cut down to size of course ) will still be tricky because it will be very loose and won't stay on tight and in the shape of the mold.

One reason I suggested the MACWAX but my apoligies for not explaining that the product is a spray on releasing agent, i.e. in atomised form ideal for unusual shapes reproducing absolute intricate detail like figurines, castings and the like and as you know you can manipulate the rubber mould while removing it from the cured casting, and the rubber will return to it's original shape, again one reason I like using it.

Just reading the side of the MACWAX tin and it states good for "polyester epoxy and......"

But again it's only a suggestion it's up to you there's lots of releasing agents' out there.

Good luck with the project!