I hope this can become a comprehensive list of my experiences when casting with different concrete and plaster mixes. There are many options on the market, and this is just the beginning. All needs, uses and skill levels are different so what might work for one mold, might not work for another. Use this list to as a reference to help you pick the best option for your project!
*If you are planning on using our molds for production this information should not be your sole basis for making decisions. Please do your own research.
Cement 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.
Cement
Cement All - Best beginner option
Strength 9,000 psi
Smoothness +++
Bubbles +++
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 it does have an accelerator in the mix which does cause silicone shrinkage at a higher rate. With good mold care, it really is one of the best options out there.
White Outdoor Mix
Strength Unknown
Smoothness +++
Bubbles +++
Available on Amazon or your local craft store, this white concrete mix creates beautiful casts. Often sold under different brand names, the properties of all I've tested are similar. If you are looking for a white cement this is an easy to find option.
Quikrete Water Stop Cement
Strength 5,500 psi
Smoothness +++
Bubbles +++
I wanted to test this option specifically for planters, as it offers good water resistance. The color is a dark grey and creates a very smooth surface. Set time is incredibly quick so you must work fast.
Direct Colors White Concrete Countertop Mix
Strength Unknown
Smoothness ++++
Bubbles ++++
While similar in appearance to the White Outdoor Mix, I find this option much easier to work with. The texture of the mix is much smoother and consistent to cast. The price and shipping options for small quantities make this an attractive all-around option.
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 to find a local supplier for some of these plaster. We use both Matrix Dryve™ and Hydro-stone for many of or samples in house.
Plaster of Paris
Strength 2400 psi
Smoothness ++++
Bubbles ++++
The largest benefit to Plaster of Paris is that it's easily to find and inexpensive from most hardware and craft stores. It creates a super smooth surface, and readily takes pigment. The major downside is the lower strength.
Perfect Cast
Strength "5x stronger than ordinary plaster"
Smoothness ++++
Bubbles ++++
Available from Amazon.
Matrix Dryve™
Strength 6,500 - 9,500 psi
Smoothness ++++
Bubbles ++++
Hydrocal White Gypsum
Strength 6,000 psi
Smoothness ++++
Bubbles ++++
Hydrostone Plaster
Strength 14,000 psi
Smoothness ++++
Bubbles ++++