Materials For Casting

by Kalynn Tupa Oct 27, 2023

Updated Oct 2023

Our silicone molds have a self-releasing property, which means they release the casted object easily without the need for additional release agents in most cases. Concrete, plaster, resin all work with our molds. All needs, uses, and skill levels are different so what might work for one mold, might not work for another. I am going to focus on concrete and plaster as they are the most common used materials for our molds. Use this list to as a reference to help you explore the best option for your project.

If you are planning on using our molds please conduct your own testing and research. Abrasive materials and exothermic reactions will degrade silicone.

A large consideration is availability. A bag of mix can be very expensive to ship so finding something locally available can be important. I have focused on mixes that are pre-mixed but offer a basic recipe for each if you don't have it available in your area.

Home Improvement Big Box stores, i.e. Lowes or Home Depot
Building Supply These are usually owned. The few I have visited have an office you purchase thru, then a drive up order pickup. This is where we source ours.
Pottery Supply A great source for plasters and raw materials if you are near one.

Concrete vs. Plaster Our molds support casting a variety of materials. The two most common choices are concrete and plaster. We'll review some commonly available options for both types of casting material

Concrete

For casting with our molds you concrete mix will be combination of Sand + Cement + Water. There are a variety of pre-mixed options as well as the option to mix your own.

If you are looking at any concrete options, a few things you will want to check.

What is the recommended thickness. Many mixes are only intended for thick slabs and might not work will for thin applications like jars.
What is the base cement. CSA or Portland Cement. CSA cement is harsher on Silicone molds
Water Reducer has become a must for me when casting concrete. I like a pourable mix and this makes it easier to use.

DIY Concrete Mix

Strength	Cure Time	Average Price	3" Pot	Weight
3,000-5,000 psi	24 hours	<$1 per kg	$.26	275

Many concrete mixes sold in stores include an aggregate and are intended to be cast thick. This makes creating your own concrete a great option. Cement is not concrete and should be mixed with sand and/or additives when using our molds . There are many variables and additives when it comes to concrete mixes.

Water ratio 5 to 1 by volume

40% Cement Portland Type 1
60% Fine Sand

There are a variety of additives you can source to make your mix stronger, easier to pour, etc.

Cement-All

Strength	Cure Time	Price	3" Pot	Weight
9000 psi	1-2 hours	$1.08 per kg	$.35	280

Cement All is a fast curing concrete mix that is easy to work with. Cement All dries to a warm concrete tone with a smooth texture. I've found the key to minimizing holes and voids is mixing to the proper consistency. Something similar to cake batter works well. If you are just starting this is an easy to find and affordable option. Please know its base cement is CSA which does cause silicone shrinkage at a higher rate. With good mold care and a mold replacement schedule, it really is one of the best options out there.

If want to try to DIY a Cement-All look for CSA cement + silica mixes as your starting point.

Buddy Rhodes Artisanal Mix

Strength	Cure Time	Price	3" Pot
8793	24 hours	$4.88 per kg	$1.46

A concrete mix made with fine sad for sculptural and craft projects. Dries to a white color. This is based on on a GFRC mix concrete and dries to a bone white.

This mix has a base of concrete mix with additives.

GFRC Mix

Strength	Cure Time	Price	3" Pot
6000 psi	24 hours	$2.30 per kg	$.70

Glass Fiber Reinforced Concrete is a mixture of Cement + Fine Sand + Fiberglass Strands + Polymer + Additives + Water. This mix is commonly used for concrete countertops. The fiberglass strands add strength much in the same way steel adds strength to large slabs. There are a variety of brands out there. It is popular for concrete countertops so it might be readily available in your area. I think for the purposes of smaller concrete castings, there are better alternatives.

Plaster

There are a few different Gypsum options available on the market. I am just going to hi-light the options that are have properties in line with casting with silicone molds. Check a pottery supply store or building supply to find a local supplier for some of these plaster. Plaster casts are much easier to get without bubbles.

Jesmonite

Strength	Cure Time	Price	3" Pot	Weight
	1-2 hours	$11.86 per kg	$3.55	231g

This is a material that is a gypsum mixed with a acrylic polymer liquid. There are many dupes but I have never found anything that creates the same plastic like casting Jesmonite does. The downside is the price per object. When compared to other plaster castings I can't say it justifies the price.

Aqua Resin

Strength	Cure Time	Price	3" Pot	3" Pot Weight
	1-2 hours	$11.86 per kg	$3.55	230g

This is a material that is a gypsum mixed with a acrylic polymer liquid. Similar to Jesmoite in that it is a two part system. It cast in a muddy color, not a true white like some of the alternatives.

Matrix Dryve™

Strength	Cure Time	Price	3" Pot	3" Pot Weight
6,500 - 9,500 psi	1-2 hours	10.25 per kg	$3.07	208g

I tested Matrix Dryve as good USA alternative to Jesmonite. It is a polymer modified plaster mix that is just add water. It creates a strong casting that mixes well.

Hydrocal White Gypsum

Strength	Cure Time	Price	3" Pot
6,000 psi	2-3 hours	$1.68 per kg	$.5

Hydrocal White Gypsum is a cement + gypsum mix that casts easily, made by USG. It does contain cement which is considered abrasive to silicone.

Hydrostone Plaster

Strength	Cure Time	Price	3" Pot	3" Pot Weight
14.000 psi	2-3 hours	$1.36	$.41	230g

By USG, Hydrostone is a cement+silica+plaster mix that cast well, is affordable, and should be easy to source. It does contain cement which is considered abrasive to silicone.

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