Materials for mould master

[Nicoolai]

Hi all,
I lurk here a lot and dream about making all kinds of props.
I want to resin cast some stuff but I'm wondering what materials to use for my master.
I see a lot of laser cutting of acrylics and the likes, but laser cutters are a bit beyond me, for now atleast.
I am more likely to invest in a scrollsaw or something like that.

So my big question is, what kind of materials should I aim for, with regards to creating my masters with that?
Would EVA Foam work, or does the soft surface work against me?
Should I go for MDF? Other woods? Plastics?

 

[TazMan2000]

You can use a wide array of materials for making masters, however I would stray away from EVA foam because of its flexible nature. Still it is possible to use almost any material as long as it's properly prepared and sealed. if you have never made a mould before, I would visit YouTube and search for the many videos on resin casting.

TazMan2000

 

[ultraman]

and stay away from materials with sulfur in them...i will keep your silicone molds from curing.

 

[Zinger]

You didn't say what you're trying to mold. How complex is your positive?

For simple shapes, I use balsa. You can cut the shape out in layers, glue it together and sand it smooth. Pretty easy if you have a palm sander and cheap.



After you get the shape right and sand the balsa with ~220 grit, coat it with several layers of gesso and sand to 400 grit. Then cover with a high build spray primer, sand to 400 grit and polish with a finishing pad. That will give you a very nice surface.



For more complex shapes, modeling clay or 3D printing are good options. Though, as Ultraman said, stay away for sulfur based clay if you are using silicone for the mold. Sulfur is Hell on silicone, especially platinum cure silicone.

The raises the question, what are you making the mold from? If your master is a simple shape with no undercuts, you can use plaster, alginate, hydrocal or even home-made silicone molds using caulk. For more complex shapes or anything with even a slight undercut, you'll have to use silicone or latex.

Brick in the Yard mold supplies has an extensive library of very informative videos. They've helped me a lot.

https://www.brickintheyard.com/pages/video-library

 

[cavx]

Addition Curing Silicone pending, the only two things I have had issues/reactions with is air cured products and certain super glues.

I used Shoe Goo once to build up a part on the master as it flowed nicely into a slot that I needed to thicken up. It set up and felt really smooth. I poured the silicone and it was a slimy mess where ever the silicone touched the Shoe Goo. I can only assume this is the same reaction as when additive silicone touches condensation cured silicone.

Generally when molding, you need to secure the parts to the base of the mold box and whilst hot glue works a treat, it can prevent the smaller parts sitting flush. Super glue should be a go to product for this. What I found was that Glues like Zapper-Gap with the kicker are fine, but any normal superglue will react. Again, leaving the point of contact slimey and uncured. I ended up washing the molds with dish soap and hot water and that removed the non cured part and the rest of the mold seemed OK.

Surface prep is super important. You have to remember silicone will pick up EVERY detail including dust particles and your finger prints. I made some clear stands for Star Wars figures and each pull from the mold has my smudged prints. Not 100% clear because I did rub the master part down, but not well enough. The result is OK in solid colours but looks crap in the clear that I wanted to cast them in. The only way to fix this is make a new mold. Lucky these parts are small and throwing away the old mold is not such a big deal.

 

[Nicoolai]

Thank you all for your answers. This is all great advice.

You didn't say what you're trying to mold. How complex is your positive?

For simple shapes, I use balsa. You can cut the shape out in layers, glue it together and sand it smooth. Pretty easy if you have a palm sander and cheap.

View attachment 734903View attachment 734904View attachment 734905

After you get the shape right and sand the balsa with ~220 grit, coat it with several layers of gesso and sand to 400 grit. Then cover with a high build spray primer, sand to 400 grit and polish with a finishing pad. That will give you a very nice surface.

View attachment 734906

For more complex shapes, modeling clay or 3D printing are good options. Though, as Ultraman said, stay away for sulfur based clay if you are using silicone for the mold. Sulfur is Hell on silicone, especially platinum cure silicone.

The raises the question, what are you making the mold from? If your master is a simple shape with no undercuts, you can use plaster, alginate, hydrocal or even home-made silicone molds using caulk. For more complex shapes or anything with even a slight undercut, you'll have to use silicone or latex.

Brick in the Yard mold supplies has an extensive library of very informative videos. They've helped me a lot.

https://www.brickintheyard.com/pages/video-library

This is exactly what I plan to do.

Are there any other materials I should know of?