Concrete. Some think it’s just a concoction of cement, sand, stone and water, something you slap into a hole to keep a gate post upright or pour for a
Concrete. Some think it’s just a concoction of cement, sand, stone and water, something you slap into a hole to keep a gate post upright or pour for a patio where you can kuier with a Klippies and Coke. But in truth, it’s one of the most quietly brilliant materials on Earth. It doesn’t shout for attention, it’s not glamorous and most people don’t realise just how technical it is. But look around, chances are, something within arm’s reach is either made from concrete or sitting on top of it.
It’s everywhere. Sidewalks, bridges, buildings, stadiums, even the mall floor that your kids use to skid across in school shoes, it’s all concrete. In fact, it’s the second most consumed material in the world, right after water. And still, it gets less recognition than the car guard who expects a tip after watching your car for exactly one minute.
So then, what is concrete really?
Think of it like a Christmas cake. Not the boxed kind, but the proper one your gran used to make. Concrete is the final product of carefully combined ingredients, cement (your flour), water (your milk), sand and stone (your sugar, nuts and dried fruits).
Get the mix right and you’ve got something solid, dependable and built to last through any weather, just like gran’s Christmas cake, which somehow survives for years. But get the ratios wrong and you’re left with a weak, cracked or sad concrete slab… or, in cake terms, a sad, sunken mess so bad even your dog skeefs you out.
Concrete Mix Designs
To avoid that kind of disaster, you need a proper recipe or what we call a mix design. It’s your blueprint for making the exact type of concrete you need, whether you’re building a driveway, a dam wall or just trying not to repeat the Great Cracked Patio of 2021.
A mix design is a guide to getting the right balance of materials: cement, water, fine aggregate (like sand), coarse aggregate (like stone) and admixture. The mix isn’t just about making something hard; it’s about getting the right kind of hard. Whether you need concrete that can handle heavy loads, flow easily into complex formwork, survive freezing winters or just look smooth enough for a polished floor, the mix design sets the stage. Understanding the type of concrete you need helps with the design of the mix. Key factors in a good mix design include:
• Strength requirements – How much load it needs to carry without cracking like a dry rusk.
• Exposure conditions – Will it face rain, chemicals, salty air or just the occasional spilt beer?
• Workability – Can you actually pour and shape it without a wrestling match?
• Durability – Will it still hold strong 10-30 years from now like grans Christmas cake?
• Economy – Getting the performance you need without breaking the bank or over-engineering it like a government tender.
Once we know what kind of concrete we need, the next step is to look at the materials we’re working with. You can’t expect top-quality concrete if you’re using second rate ingredients. It’s like trying to bake a cake with expired milk and self-raising flour that’s lost the will to live. We need to understand the qualities of each material, cement, sand, stone and water before we can create a reliable mix design. The better we know what’s going in, the better the concrete comes out.
Defining the right type of concrete and using quality materials in the correct ratios, that’s what a mix design is all about. It’s the recipe that tells you exactly how much of each ingredient to use, by weight (or occasionally by volume), to get the performance you need. No guesswork, no shortcuts, just a proper plan to make sure your concrete actually does its job.
Consistency, consistency, consistency
Let’s say you’re helping your mate build a concrete braai area over two weekends. The first batch? Spot on. Smooth, strong, easy to work with and everyone’s impressed so far. But the next weekend, you get a bit creative: add extra water “just to make it easier” and toss in some mystery stone you found behind the shed because you ran out of the proper stuff. That second batch sets weird, starts cracking and now your mate’s giving you the side eye every time he flips a chop.
Even small changes, like a slightly wetter mix or switching to a different stone can mess up the mix. Concrete doesn’t forgive, it remembers.
So, how do you keep it consistent? Good news: there’s a process for that.
Use the same consistent materials
If you change the cement, sand, stone, admixture or even water, you need a new mix design. Full stop. You can’t just swap things out halfway through a job and hope for the best. That’s like suddenly using almond milk in your rusk recipe and expecting no one to notice. They will. And they’ll be upset.
Stick to the same suppliers, same sources and same specs unless you plan to redesign everything.
Control the moisture in your sand
Sand holds water. If it rained last night, your “perfect mix” could suddenly turn into concrete soup. That’s why moisture control is critical.
Here’s the rule of thumb I give clients:
Check the moisture in your sand every morning, after rain, after any new delivery and every afternoon. The more accurately you monitor moisture, the more consistent your concrete will be.
Do simple moisture tests and adjust your water/sand content accordingly. A little effort here saves a lot of stress and failures later.
Measure, don’t guess
Yes, actually measure. Not “a bit of this and a touch of that.” You’re not making a salad. Concrete needs precision.
Follow the mix design and weigh your materials accurately, cement, sand, stone, water, the works. Too much sand? Your mix will need more water. More water? Less strength.
Accurate weighing and measurement is key to consistent concrete. And don’t forget your scales, make sure they’re calibrated regularly by someone who actually knows what they’re doing. Not your cousin with a screwdriver and YouTube.
Mix properly
None of this “give it a swirl and hope” nonsense. Get a proper mixer or a very committed friend with strong arms and no plans for the weekend. If you’re using a truck, make sure the blades aren’t worn down to nothing. Ensure the mix is properly blended and uniform from top to bottom. You don’t want one wheelbarrow of stoney sludge and the next full of sloppy soup from the same batch.
Testing, testing, 1-2-3
Slump tests and cube tests aren’t just box ticking exercises, they’re your early warning system. Do them and do them often. The more test data the merrier.
If your concrete looks suspiciously like pancake batter, take it as a red flag, something’s not right. And if your cube strengths are all over the place? Something’s gone wrong, go back and check your mix, your materials, your moisture, your weighing, your mixing or even your testing. Somewhere along the line, you’ve slipped.
Testing gives you peace of mind. It proves your concrete is performing like it should and gives you the confidence that you’re not just pouring expensive porridge. Think of testing as a small investment that could save you from big disasters and even bigger repair bills.
In the end, concrete isn’t complicated
Concrete might seem like just another building material, but as you’ve now seen, there’s a whole science (and a bit of common sense) behind doing it right. Get the mix design right, use good quality materials, keep everything consistent and test like your project depends on it (because it does). Whether you’re building a hospital, a mall, a home or just a humble braai spot, good concrete is no accident. It’s measured, managed and mixed with purpose. Skip the shortcuts and you won’t just save yourself from cracks, you’ll save your wallet and your reputation.
Still unsure? Call the pros.
As simple as it all sounds, if you’re still unsure, call in the experts. We’ll help you get it right the first time, save costs and avoid becoming the next concrete horror story your colleagues joke about at braai’s.
