In our Simple Concrete Mixing article we gave the minimum details you need to start working with cement around the house and garden. In this article we’ll be giving more information about different mixes and what they can be used for.
In our beginners’ article we kept the mix simple, a general purpose sand and cement mix (six parts sand to one of cement). This mix, or a similar one but with one part sand replaced with one part lime, can be used for laying blocks or bricks and re-pointing brickwork.
Mixing with Aggregate
To lay patio slabs or paving stones you need a stiffer mix, using only 1:4 and less water. But in reality it’s not that often that you would use just sand in the mix, you would add an aggregate of some sort that has larger granules than sand. This is partly to give strength but also to make the mix cheaper, particularly when you are using a lot of cement in a place where it will not be seen.
For example when fixing fence posts in the ground or making a base for a shed or greenhouse you could use a mix of one part cement to two parts sharp sand and three parts coarse aggregate. Coarse aggregates have the larger granules that you need to take up space economically.
Ballast is a trade term for general aggregates, often made up of sharp sand and gravel or small stones. It’s often sold by the size of the largest granules, for example 10mm ballast. You might sometimes want to use ballast in a general purpose mix, like 1:4 cement to ballast. Or for the foundations for a garden wall use 1:5 cement to ballast.
For a finer mix, perhaps to render a block wall in the garden, use one part cement, one part lime and six parts plastering sand. Mix this to a consistency that will hang on to a trowel when it’s turned upside-down.
Note that although you can use shovel loads as a rough measure with sand and cement, it can be a bit trickier with aggregates and ballast. This is because it’s easier to get more ballast or aggregate on a shovel than cement or sand, so a 1:6 ballast mix can end up being closer to 1:8.
Use a bucket or some other suitable container to measure the volume of the ingredients you are using.
If you have a large job you might want to take advantage of a number of websites that offer concrete calculators. With one of these calculators you fill in the dimensions of the job and the mix you are using and they will tell you how much of each product you need to order.
But it has to be said that if you are using a concrete calculator you are probably going a bit beyond the remit of a site called DIYBasics. So put ‘concrete’ into the search box on this page and you should be able to get more advanced information from one of our other sites.