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What is the Best Ratio for Concrete Mix? A Simple Guide 

The Magic Numbers

Whether you’re tackling a big project or doing a basic DIY, concrete is the first choice among many for its durability and weather resistance. But what is the best ratio for concrete mix? Fortunately, with concrete, it’s hard to go wrong. Let’s explore the top three concrete mix ratios as recommended by experts.

The C30 Mix: 1:2:3

To better understand ratios, remember that they are always in the order of cement: fine aggregate: course aggregate. Fine aggregate refers to loose product like sand, whereas course aggregate is something more like stone or gravel. You can also buy combined aggregate or ballast concrete mix at the shops, which is a bit more convenient. But in this case, you’ll be mixing one part cement to three parts fine aggregate and course aggregate. This ratio produces concrete with a strong resistance. This makes it ideal for walkways, footpaths, and floors. If you’re looking to put a new floor in a shed or repave the entrance in your garden, this is a great mix. It’s not the absolutely weakest, but it isn’t the strongest, either–so avoid using this ratio for load bearing paths, as it could potentially crack if a lorry drove over it.

The C20 Mix: 1:2:4

Compared to the previous ratio, this one produces concrete with a weaker resistance. It uses four parts course ballast. The course materials act as a filler here, so it’s great for making large batches of concrete that may not be visible or load bearing. In particular, this ratio is great for posting fences or other items. If you’re planning on using concrete for a DIY, such as a pot or vase, this ratio is great. It might be slightly difficult to mix in small batches, so consider buying combined aggregate instead. With combined aggregate, the fine and course materials are pre-proportioned, so your ratio will be something like 1:2 instead. 

The C40 Mix: 1:1.5:3

This ratio is the strongest of the three. The 40 refers to the amount of resistance, measured in Newtons/mm2. So this mix will produce concrete that has 40 N/mmof resistance. This is a level of durability suitable for paving roads, foundations, support beams, and more. Of course, large scale projects that require even more strength will need the addition of reinforcements. Most home improvers won’t need to produce a mix this strong, but it is helpful to know if you plan on redoing your drive or are looking to pour a foundation for a new structure.

Picking Out What’s Best for You

For most folks working on home improvement projects, you can’t go wrong with a C30 or C20 mix. But if you’re worried about the long term durability of your concrete, consider asking a contractor for advice. Remember that when it comes to concrete, it’s not all about the ratio. You also have to worry about the moisture content and the cure time. Fortunately, concrete is a fairly easy building material to navigate. It’s incredibly strong and versatile for so many projects. In fact, some people are beginning to fancy the appearance of plain or unfinished concrete in their homes, as it gives a chic industrial look. Happy mixing!