How to Mix Concrete using a Cement Mixer
This is a complete guide on How to Mix Concrete using a Cement Mixer. Before we start, it is important you understand the basics about concrete.
The concrete you will be making consists of 3 main ingredients:
Cement: Is rarely used on its own when it comes to construction. But, it works great as a binder. In this case it is binding the sand and gravel together present within the ballast, helping to form a strong stable material which is concrete.
Ballast: There are many variations of ballast out there. Ballast is simply a sand and course gravel mix.
Water: Is used to mix the cement and ballast together, to form a consistent smooth concrete.
Mixing concrete is more difficult then people think. This is because concrete is very sensitive to the ratio of cement, ballast and water. This article explains how to make a particular ratio of concrete called C20, which is 4 parts (all-in-one ballast) to 1 part cement. This is considered an ideal grade for most domestic applications such as foundations for garden walls, paving, shed bases, garage bases and extensions. The 20 in C20 actually means the concrete can withstand a compression of 20 Newtons per square millimetre over 28 days. Or in less geeky terms, 203.94 kg per square cm. This gives you a good idea how strong your concrete really is!
Calculate Ballast & Cement Quantities
Below is a guide on how to calculate the weight of ballast and cement needed for your project.
1. Calculate the Volume of your Foundation
Total foundation volume = Length x Width x Depth
For example, a foundation measures 1m X 1m X 0.5m
Total volume = 0.5m3
2. Calculate the Ratio of Cement and Ballast from this Volume
To calculate the weight of ballast and cement needed, we first need to know the total weight of the final product, being the concrete. In general concrete weights about 2400kg per cubic meter, this is known as the density of concrete.
Total weight off Concrete = Volume of Cement needed X Density of Cement
For example, if the volume of concrete needed for the job eqauls 0.5m3.
Total weight off Concrete = 0.5 X 2400
Total weight off Concrete = 1200kg
Concrete = 4 part ballast : 1 part cement
Ballast required is (1200 / 5) X 4 = 960KG
Cement required is (1200 / 5) X 1 = 240KG
How to Mix Concrete using a Cement Mixer
By this point, you should have measured out the amount of ballast and cement you need, in weight. Follow the guide below to mix your ballast and cement together:
- Clean your shovel and wheelbarrow, ensuring no mud or dirt is left on either.
- Set up your mixer, ideally close to the ballast and cement. Mixing concrete is a messy job. If you are working on top of patios or block paving, we recommend you protect the surface with sheet plastic or ply. Once concrete dries, it stains and is extremely difficult to remove.
- Fill two builders buckets to the top with water only.
- Have a third empty bucket close by. This third bucket is what you will be using to gauge the mixture with.
- Pour under a quarter of one bucket of water in to the mixer and make sure the whole inside of the drum is wet.
- Fill your gauging bucket to the top with ballast, then pour this into the mixer.
- Add a little bit more water.
- Add another bucket of ballast and repeat the same process.
- Now fill the bucket with the cement and pour that on to the wet ballast and allow a minute or two to mix. Stand away from the mixer as much as possible to avoid breathing the cement dust in.
- Once the mixer has worked the cement in to the ballast add the last 3 buckets using the same process until you have a nice grey mix that is wet, but not sloppy and spilling out the front of the mixer.
- Once you are satisfied with the mix, put the wheel barrow in front of the mixer.
- Only pour half of the mix out to make sure you are comfortable with the weight. if so, then pour the rest out until the barrow is three quarters full. Don’t fill the wheel barrow right to the top, this will help prevent spillages.
- Once you have the wheelbarrow at the foundation, shovel the concrete out of the barrow in to the hole, until the wheelbarrow is light enough to tip. If you are worried the sides are a bit delicate you can uses a scaffold board or timber to put on the edge of the foundation to tip the wheelbarrow on to, to prevent damaging the sides.
- Get a piece of timber or something to push into the concrete (not your spirit level), and push the concrete about to keep it level about every quarter of the filling of the foundation. Repeat this until the concrete is about an inch from the top of the foundation.
- Once you have the desired height of the concrete, use the timber to rest on top of the wet concrete and tap evenly throughout the foundation. At this point you will need your level to put on top of the timber, to see when the foundation is level.
- Let the concrete set for 24 hours.
- Clean your equipment and tools with water. If you don’t do this then the concrete will set on anything you have used.