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Posted: 26th April 2023 | Author: Adam Brown
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Planning a DIY paving project, or building something more substantial? One of the many materials you’re likely to need is cement, combined with just the right amount (and type) of sand to get the perfect mix.
But how much sand and cement do you need to buy? Read on to find out, as we’ve put together a helpful guide covering everything you need to know.
First of all, it’s useful to know a little about how cement is manufactured. Once the raw materials of limestone and clay have been mined, they’re fragmented and transported to a processing plant. This is where the materials are crushed and mixed.
The main part of the process is calcination. This is where the materials are heated to very high temperatures (up to 1,400°C) by huge rotary kilns.
At the end of the process, what is left are small dark grey nodules a few cm in diameter. To turn these into the powdery cement mix you see in building supplies stores, the nodules are milled until fine. Finally, gypsum may be added, before the cement is packaged ready for shipping.
Cement is used to make both concrete and mortar, which vary depending on the types and ratio of materials added into the mix.
To help you plan your project and work out how much cement you’ll ultimately need, here’s a rough guide to the ratios for each:
Once you’ve mixed your materials, you’ll now have concrete rather than cement. This usually takes around a day to set, although it depends on the mix as well as the weather conditions.
If you’ve laid a floor or patio with your concrete mix, you shouldn’t move or walk on it after 20 minutes have passed. This could ruin the integrity of the concrete, as well as the finish.
After around 24 to 48 hours, your concrete surface should be hard enough for you to walk on. This is useful to know if you’ve got other jobs to get on with, or other trades coming in as part of the project.
But there is another stage to the process, known as curing. This is where the concrete continues to harden. It can take anywhere between seven and 28 days for the concrete to reach its full hardness. If you’re planning to bring any machinery, vehicles or other objects onto the surface of your new slab, it’s recommended to wait the full 28 days just in case.
Now to address that all-important question - how much cement and sand do you need to buy for your project? The quantity of materials you’ll need all depends on the nature of the job.
This can sometimes be tricky to work out. Under-order and you’ll be left short, unable to finish the job. But get too much and the excess will be wasted, as well as costing you money you didn’t need to spend.
The easiest way to work it out is using a cement calculator. You’ll need to have the dimensions of your concrete slab, base or screed to hand, making sure you have width, length and depth noted down. The calculator will estimate how many cubic metres or tons of cement you’ll need, and the equivalent in bulk or 25kg bags.
The amount of cement you’ll need is likely to differ depending on whether you’re making concrete or screed, due to the different ratios of materials in each mix. This is another thing a good cement calculator can help you with - simply select concrete or screed, along with your measurements.
Another fairly major drawback of ordering too much cement is that it can go off. If you have spare bags lying around, you might think you’ll be able to use them for another project at a later date. But you’ll need to check the expiry date on your cement, as you might be surprised at how soon this is. The best way to prolong your cement storage is to purchase plastic bagged cement which gives 12 months shelf life if stored correctly and offers an element of weather resistance to be stored outside.
Can you use cement if it’s gone off? Unfortunately not. This is because the cement is unlikely to mix properly, especially if it’s gone hard or lumpy. This means you won’t be able to get a smooth mix. Cement that has passed its expiry date is likely to produce poor quality concrete, which could potentially ruin your project.
There are also safety issues to consider. In old cement, the skin irritants in the mixture can potentially become more potent.
If you do end up inadvertently using cement that has passed its expiry date, don’t panic. If there are any irregularities in the finish, you may be able to patch and repair it using a specialist mix.
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The Author: Adam Brown
With a background as a Mechanical Engineer, I started Nationwide Supplies alongside my brother with a vision to modernise what seemed a stuck-in-its-ways industry in the builders merchant sector. Since 2011 it has been my goal to source quality products at the correct prices to be able to offer a saving to customers along with high quality customer service which offers quick delivery and superior technical knowledge in the industry.
