Model Railroading > Better Silicone Rubber Molding and Resin Material?

I bought some cheap silicone molding material and resin from Michaels and Hobby Lobby in the $20 range. It is OK for making molds for bridge piers and abutments made of Hydrocal, but not great to mold small resin parts. it doesn't pick up the detail well.

I also need something where the rubber mold lasts so I can make additional bridge piers, abutments and resin detail parts for duplication or resale. Do I need to invest about $100 for better detail and longevity of the molds?

I bought a kit from Micro Mark some years ago for about $100 and it worked good for resin casting.*** But perhaps I can get the same thing directly from the manufacturer?

I know that some of you folks here have experience in this.

***The kit has been out of stock at MicroMark every time I've checked,  and though you can buy the resin from them separately, the rubber mold used in the kit is out of stock too.

Victor Baird



Edited 4 time(s). Last edit at 07/22/25 20:00 by wabash2800.

I have done a ton of molding and casting, and I would highly recommend you look at Smooth On.  They have a literal ton of different products, and their pricing is pretty good.  The quantities you buy in are a bit larger, but not ridiculous.  As a bonus, they probably have a dealer not far from you.

https://www.smooth-on.com/

Brian Hahn

Thanks Brian.

Victor Baird

Posted from Android

You might also check on line for TAP Plastics. They specialize in that stuff. They have several locations in the Bay Area.

Posted from Android

An extensive selection of Smooth On products are available on Amazon.

I second the Tap Plastics series of Silicone mold material and urethane casting resin. I've used these materials for years. The molds last darn near forever as long as you take care of them, for example, using mold release to make pulling the piece easier. And as for detail, clean your fingers before working with the pattern or the mold, and resin, will pick up fingerprints.

Jeff Johnston
thesugarpineshop.bigcartel.com

 

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Thanks for your descriptive posts on Trainorders and your private reply to my private email the other day

That's what makes Trainorders so special.

Victor Baird

Jeff_Johnston Wrote:
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> I second the Tap Plastics series of Silicone mold
> material and urethane casting resin. I've used
> these materials for years

Have you found that parts made of TAP get brittle over the years?  Or does it seem to hold up well?

I made my first resin molds and castings back in 2006.   My first 'chunk' of excess resin with the stir stick still embedded in it is still on my desk, 

Micro Mark CR600.   It has yellowed slightly over the years, but still flexible, hasn't cracked.   Neither have the parts I've made.

I started with the 1:1 rubber, too soft.  Graduated to the 10:1 high performance stuff, those molds are still going strong.....IF.....

1)  You must use silicone spray/mold release each and every time
2)  You must lightly talc the molds and air gun any excess off.
3)   I've checked with a ruler and micrometer.   I know everybody says resin shrinks, but on my stuff it has NEVER been a problem.  I have confirmed that the Smooth-on stuff has a shrink factor, I don't deny it.

I've got molds now that are probably 10 years old.  Depends on the design.  I'll probably get 50+ parts out of a set before I have to make a new one.

I think it's becoming a lost art with high-quality RP modeling.  You have to be a good scratchbuilder to make masters, I am, but at long last the surface qualities of RP printing can match whatever I can do.    The only thing I can do that still evades the RP guys is make metal parts from the bismuth mixes, printing in metal is beyond the home systems, and I can make some pretty nice parts from rubber molds and bismuth that solve the weight problem, and I've also made hybrid parts with metal poured in resin, wire imbedded in resin, etc.   

I also perfected pressurized injection of CR600 into multi-part rubber molds rather than the usual 'squish' or flat pour.  That was a turning point.

Thanks for the input Randgust. Does a vacuum mold (pressurized injection?) provide better detail for small parts? What does a vacuum set-up for rubber molding run for the model railroader?

Victor Baird



Edited 2 time(s). Last edit at 07/28/25 18:10 by wabash2800.