WORKING WITH CONCRETE

Mixing concrete and getting the right concrete mix ratio is vital for a durable and long-lasting job.

Concrete is a mixture of cement, sand (fine aggregate), small stone or gravel (coarse aggregate) and water. It has many applications, from fence posts to motorway bases and, because of this, there are many different concrete mix ratios that the constituents can be mixed to with each resulting in a different strength of concrete.

In terms of what different strength concrete mixes there are, they range from C10 up to C40, with C10 being the weakest and C40 being the strongest.

What's the best concrete mix ratio for general domestic jobs? 

As a quick answer, a concrete mix ratio of 1 part cement, 2 parts fine aggregate (sand) and 4 parts coarse aggregate will cover most general domestic jobs.

Concrete mixed at this ratio is generally known as a C20 mix and it's more than suitable for garden paths, concreting fence posts, shallow retaining wall foundations, some extension bases, shed bases and many other domestic and commercial applications.

C20 is a medium-strength concrete mix. This means it will attain a strength equivalent to withstanding a compression of 20 Newton's per square mm after 28 days. More details covering types and strengths of concrete and how they should be used can be found below. This mix is not suitable for house foundations.

If you are planning any major renovation or building project, your architect will probably specify the strength of concrete required for your project. If you are at all unsure on the strength you should be using, check!

Concrete mix ratio for a C20 and C20P (Portland) mix 

The proportions of materials for a C20 and C20P (P = Portland cement) concrete mix are:

• 1 part cement

• 2 parts fine aggregate (sand)

• 4 parts coarse aggregate

If you are using premixed ballast, then:

• 6 parts premixed ballast 

• 1 part cement