Concrete Mixing Ratios
Concrete is made up of a mixture of cement, sand and stone. These ingredients need to be mixed together properly, in the correct ratio, using a high quality concrete mixer.
The correct mix ratio of cement to sand and stone depends on what the concrete is to be used for. If the application requires harder concrete, the cement ratio needs to be increased; for rougher applications, more aggregate (stone and sand) is required. We have listed recommended ratios for concrete mixture below, though these are guidelines - the best proportions for your application may also depend on the quality of sand/stone used.
Most standard applications: 1 part cement, 1 parts sand, 4 parts stone.
Foundations: 1 part cement, 3 parts sand, 6 parts stone.
Rough Mass Concrete: 1 part cement, 4 parts sand, 8 parts stone.
Water Tight Floors, Tanks, Pits etc.: 1 part cement, 1.5 parts sand, 3 parts stone.
To mix the ingredients together to create concrete, you should firstly add water to the mixer. You should use around 7 litres (1½ gallons) to begin with, using more or less depending on the type of mix required. Then add some aggregate, before adding the cement, to avoid sticking. Keep working consistently to the same ratio as you mix up new batches of concrete, to ensure that you get the same, consistent, high quality concrete mixture throughout the project.
How to get a good concrete mix
The way that you add the concrete ingredients to the mixer is also important for creating a high quality concrete mix, as well as the quality and proportions of the ingredients.
The mixing should last approximately 2-4 minutes from when all of the materials have been added. If you over mix the ingredients, the strength of the concrete mixture can be reduced and it can cause segregation of the coarser aggregates.
You should stay away from low grade aggregates, as these will cause issues later on, with sinking and frost spoiling the appearance of the pour. Also, do not get the concrete mixture too wet as this can also reduce the strength of the concrete and reduce its ability to withstand weathering.
How to look after your concrete mixer
“Look after your equipment, and it will look after you” – never is this truer than with construction equipment and tools. Concrete mixers are tough and robust pieces of equipment, they will give you reliable, high quality concrete mixtures, but you should still look after them and keep them clean and well maintained to ensure that they keep on working properly and producing high quality results.
You should never throw the concrete mixture ingredients into your mixer. As this can cause the aggregate to stick to the back of the mixing drum, and this can only really be dislodged by stopping the mixer – which is certainly not ideal. Instead, steadily trickle the cement, sand and stone over the rim and into the mixer.
How to clean your concrete mixer
You should also keep your concrete mixer clean. Any material left in the drum will harden and attract more mixture in the future. This will then build up and the mixer will become useless.
You can use a pressure washer to jet wash the mixer after use. You can also use a mix of 1" (2½cm) gravel and clean water, load it into the drum and run the mixer. This will dislodge any mixture stuck to the drum, so you can then pour it out. If you use plenty of this water and gravel mixture, you can get the cleaning done really quickly. Though, do not use large stone, rocks or bricks to clean out the mixer, as this can cause damage.
If you hire a concrete mixer, you will need to clean the concrete mixer properly before returning it, as you can incur extra cleaning charges if the mixer is returned dirty.