Mixing concrete is a basic skill that all DIY enthusiasts should know how to do. Concrete is one of the most common and cheapest building materials on the planet that consists mostly of sand, gravel and cement.
Mixing of concrete is similar to baking to achieve consistent results, it is best to follow a specific recipe. There are a variety of concrete mixes for different applications depending on the strength, workability and application of the concrete.
Mixing concrete is very much a science for professionals, but for the average backyard enthusiast, it is enough to learn the basics of the concrete to get started.
When mixing concrete, it is necessary to mix aggregates such as sand and gravel together with cement powder and water as a catalyst to begin the chemical process of binding the ingredients together. Mixing concrete is a function of proportions where you measure the volume of aggregates used for the volume of cement used.
The most common concrete mix used worldwide is the 3-2-1 blend that uses three parts gravel, two parts sand and some cement. Water is added with the idea that you should use as little water as possible to make the concrete possible for what you need it for. Concrete viscosity is measured by "random" which refers to a specific test where the amount that a cone with a concrete will lose its shape when the cone is removed is measured in inches or mm. A zero-fall concrete would be very rigid and dry and prone to hold its shape, where a concrete with a six-inch or more drop would be extremely wet and not prone to hold a shape.
The mixture 3-2-1 is used so much because it is possible to fill large surfaces with concrete for relatively cheap. You can potentially only use sand and cement, no gravel, to create what is called mortar. In the 3-2-1 mixture, gravel acts as a filler and takes up a lot of space while maintaining a relatively high total strength. The disadvantage of the 3-2-1 mixture is that the larger gravel unit often floats to the surface during finishing, and is unsuitable for thin or detailed concrete applications.
The best overall mix for a DIY enthusiast to memorize and use is a simple 3: 1 mortar mix. By using three parts sand and a part mortar you can create the strongest concrete as possible as well as concrete that is easy to finish and detail with patterns, templates or stamps. By not using the gravel, the mortar will have a more even consistency, but will ultimately occupy less volume than concrete made with gravel as well. If you pour very large volumes of concrete, the gravel can be cost effective but for most DIY projects, a 3: 1 mortar mix is the way to go.
The sand you need to use for a 3: 1 mortar mix should be sharp sand or bricks or joint sand. Any place you buy sand will use a different term, so it can be confusing when you shop. All you need to remember is to avoid play. Playing sand is sand that has been washed and sterilized (this is ok) and then tumbled to soften all the edges of the individual sand grains (this is bad).
The sharp edges of the sand help to keep the concrete mixture together better than the rounded edges of the tumbled sand. Ideally, you would like to find sand from landscape supply stores that sell to you at the cubic yard. With a strong trailer you can pick up as much sand as you possibly need for almost nothing – plus the quality of the sand to make cement will be very high.
The applications for a DIY enthusiast to use a 3: 1 mortar blend are huge. Everything from fixing broken outdoor steps and stairs, highways, patios, decks, ponds, waterfalls, artificial stones, statues and much more is possible with a simple mixture of sand, cement and water.
Start with small concrete projects to get a better feel and understanding of how to work with concrete. Because concrete is so popular all over the world and is a very advanced science, you will never run out of interesting concrete applications to learn or try. Combined with being the most affordable building material on the planet and easily accessible everywhere. Learning to mix basic concrete recipes is a basic DIY project.