What's IN a Concrete Mix?

We get this question a lot

"I don't have Cement-All or Buddy Rhodes concrete products in my Country, How do I make my own mix?

In this blog I'm going to outline quickly the types of ingredients that go into a concrete mix. 

"Concrete" is a term used to describe a composite ceramic material; ie made up of several ingredients mixed together. Concrete typically contains of these four different elements:

1. CEMENT (Binder) 
2. AGGREGATE (Filler)
3. ADDITIVES
4. REINFORCEMENT

1. //BINDER// Choose one!

The binder is the material that is going to cause the reaction that hardens, holds, and creates strength in the concrete. Cement is the usual binder in concrete. My most common binder is Portland Cement. Portland Cement is a good all-around use binder.

A different type of Binder cement that we recommend is called CSA CEMENT. CSA Cement cures much faster, is harder, more dense, stronger, more resistant to UV, more resistant to water damage, and is less susceptible to efflorescence color changes. CSA cement also produces 66% fewer carbon emissions during production compared to Portland Cement. 

2. //FILLER//

Filler in concrete is any solid rocky material that isn't cement. This typically includes varying grades of sand, gravel, and/or rocks. 

For smaller concrete wares, you need smaller aggregate (filler). For example, for items smaller than 6", we use medium grit sand (beach sand) and cement only. 

For casting larger objects, you want to add larger aggregate. The size of the piece to be made, as well as the wall thickness, will help determine what size and type of filler to use. Example, an object the size of a shoebox, we recommend adding slightly larger grit sand, to potentially small pebbles (between 3mm-6mm). Using larger aggregates will generally lead to stronger and more robust concrete. However, larger aggregate will also inhibit the ability for the concrete to flow into the mold. 

3. //ADDITIVES//

There are now LOTS of different additives on the market designed to change the way your concrete works. Some additives are added in liquid form, some are dry powders. We will cover the additives more closely in a future blog. Different effects that additives can yield you are:

-Faster / Slower curing time
-Increased flowability
-Increased vertical support
-Increased surface bonding
-Increased UV resistance and weather resistance
-Improved color
-Improved physical properties
& more!

For a basic concrete mix we recommend no additives, or perhaps only Flow Control (water-reducer) if you can source it. Use a water-reducing agent to achieve a more fluid concrete mix that is easier to pour and releases surface bubbles more easily. 

4. //REINFORCEMENT//

Concrete can be reinforced with different materials to improve it's physical properties like compressive and flexural strength, surface hardness, and strength  in thin sections. 

Common types of reinforcement are fibers, metal bars, metal mesh, and fiberglass mesh. In some cases it may be appropriate to use pieces of wood or timber as reinforcement. 

Most concrete home wares, like the ones from our molds, do not require reinforcement material. If you choose to add extra durability to your products, you can begin to add a great deal of strength with acrylic fibers. For small planters and pots, use short fibers like 3/8" Long or 1/2" Long chopped glass fiber. For larger concrete pieces, or thinner pieces, use a longer fiber length like 1" or 1.5". 

Most concrete items we make do not need any kind of fiber reinforcement. 

 

YOUR BASIC CONCRETE MIX

For small concrete items (1" - 6")
By total Weight: 
18% Water
40% Cement
44% Fine Sand
vary water content as needed

 

For medium concrete items (6" - 12")
16% Water
35% Cement
29% Fine Sand
20% Coarse Sand

 

For Large Concrete Items (12"-24")
15% Water
35% Cement
20% Fine Sand
29% Coarse Sand
+Fiber Reinforcement

 

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