Concrete has a ton of applications for us humans. We use it for building structures like houses, bridges and roads. It can be shaped in molds to create blocks or formed into whole walls and when it dries it is weatherproof, waterproof and heat-resistant. Concrete is simple to make and has been used by humans since ancient times (it was used for things like the Roman Coliseum and Pantheon). It is made of two things; aggregate (like crushed rock or even sand), and cement (a glue-like binder that sets and hardens materials together, like aggregate). In many cases, cement is activated by water (hydraulic cement), so there is a chance you will need water as well.
Making your own concrete can be extremely easy. Essentially all you have to do to get started is collect an aggregate material. It can be stone, gravel, sand or even crushed up concrete. You can collect it off the ground or mine for it. In fact, it has been the most mined thing in the world throughout history.
Next you need to track down or make some kind of cement. It is commonly available for purchase, but it can also be made and in some cases found naturally. Based on the material of aggregate chosen for the application, different cements may be better than others. Portland cement is the most common cement in use worldwide, and as a hydraulic cement it requires you to activate it with water. A small amount of water used creates a thick cement which is harder to work with but stronger. More water creates a more free-flowing cement/concrete at the expense of strength and durability.
Concrete can get a lot more complicated by adding additional elements and materials to enhance specific qualities and features of the mixture, but for this article we are going to keep things simple.
Concrete needs a substantial amount of time to fully harden and set (or cure). The first three days are crucial and the concrete should be kept from getting too hot (evaporating water needed for setting) or in some cases too wet. Concrete will attain 90% of it’s hardness and strength in these first three days, but can continue to strengthen over years and even decades.
Industrial cement packages will have ratio instructions for mixtures, however a good ratio for simple concrete mortar paste is:
- 1 Part Water
- 2 Parts Cement
- 3 Parts Sand
A good ratio for a more heavy-duty concrete with more solid aggregate would look more like:
- 1 Part Water
- 2 Parts Cement
- 4 Parts Sand
- 6 Parts Gravel/Stone Aggregate
In all cases (much like baking) you should start with dry ingredients first and gradually add wet ingredients like water, in order to reach a desired consistency but not exceed it. Mixing concrete by hand can be tenuous and heavy work depending on the amount you are maxing. Make sure you mix in an apparatus which you can wash and/or drain afterwards. The absolute easiest way to mix concrete is by using a manufactured concrete mixer, or mixing bags which we sell. Small hand mixers are useful for small applications.
Just like working with any other liquid that turns into a solid (like glass), make sure you have a game plan before getting your material ready. If you are pouring concrete into molds, make sure those molds are ready to go. Don’t risk the time setting things up once your concrete starts to harden, and don’t risk pouring concrete improperly or not considering if you need to run any kind of conduit under it or anything like that. Planning is key, because concrete is permanent.