Load roughly half the water first, then the aggregate, then the cement and sand, then bring it to consistency with the remaining water. Mix for three to five minutes after the last water goes in.
That order is not arbitrary. Tipping dry cement into a dry drum cakes it onto the blades and the drum wall, and you end up with a batch that is short of binder without ever knowing it.
Batch size: what a mixer really holds
Mixers are sold by drum volume, but usable batch size is around half that. The material needs room to tumble, and an overfilled drum simply slops rather than mixing.
| Mixer | Drum volume | Usable batch | 15 L buckets | Concrete produced |
|---|---|---|---|---|
| Small electric | 90 L | ~45 L | 3 | 0.03 m³ |
| Standard electric | 120–140 L | ~65 L | 4–5 | 0.05 m³ |
| Petrol site mixer | 150–180 L | ~90 L | 6 | 0.07 m³ |
| Large petrol | 200 L | ~110 L | 7 | 0.08 m³ |
That last column is the number worth internalising. A standard electric mixer produces about 0.05m³ per batch, so a 1m³ pour is twenty batches — roughly ninety minutes of continuous work.
Loading order
- Start the drum turning before adding anything.
- Add about half the water. A wet drum stops cement sticking to the sides.
- Add the coarse aggregate. The stones scour the drum as it turns.
- Add the cement. It now meets wet aggregate rather than bare steel.
- Add the sand.
- Add remaining water gradually until the consistency is right.
- Mix three to five minutes after the last water.
With all-in ballast the sequence collapses to water, ballast, cement, water — simpler, and one reason ballast suits site mixing. Quantities are in the ballast calculator.
Measuring by bucket
Use one bucket for everything and count. A shovel load varies by 30% between people and across a day; a bucket does not.
Fill loosely and strike level rather than heaping. Mark a fill line inside the bucket if you want to remove the judgement entirely. Keep a separate marked bucket for water.
For a 1:2:4 mix in a standard mixer, half-scale batches work well: half a bucket of cement, one of sand, two of aggregate. Halve everything or nothing — rounding one ingredient and not another is how ratios drift.
Bucket counts per batch
| Mix | Cement | Sand | Aggregate | Fits which mixer |
|---|---|---|---|---|
| 1:2:4 half scale | ½ | 1 | 2 | Standard electric |
| 1:2:4 full | 1 | 2 | 4 | Petrol site mixer |
| 1:6 ballast half | ½ | 3 ballast | Standard electric | |
| 1:6 ballast full | 1 | 6 ballast | Petrol site mixer | |
| 1:5 ballast | 1 | 5 ballast | Petrol site mixer | |
Buckets are 15 litres. Halve everything or nothing — rounding one ingredient and not another is how ratios drift over a morning.
Judging consistency
You will not have a slump cone. Two tests get you close enough.
The ridge test. Drag a trowel through the surface of the mix. A correctly proportioned batch holds the ridge with clean standing edges. If it slumps back and water seeps into the trough, it is too wet.
The ball test. Squeeze a handful. It should hold together without water running between your fingers, and should not crumble apart when you open your hand.
A correct mix feels slightly stiffer than you instinctively want. If it is easy to pour, it is too wet — and too wet is permanently weaker. There is more on this in our guide to the water-cement ratio.
Keeping batches consistent
Across twenty batches, small variations compound into a slab with visibly different strength and colour in different areas.
Three habits prevent it. Write the bucket count on a board where everyone can see it. Keep the water measure fixed and adjust only in small deliberate increments. And discharge the drum fully each time — material left in the drum carries over and skews the next batch.
If a batch comes out obviously different, work out why before placing it rather than pouring it into the middle of the slab.
Working rate and planning
A realistic rate with one person mixing and one placing is a batch every four to five minutes. That is roughly 0.6 to 0.75m³ per hour with a standard electric mixer.
Plan the pour against that. Anything over about 1m³ is a long morning; anything over 2m³ should be split into formed bays or done with a bigger mixer and more people.
Two people or one
Mixing is one job and placing is another, and doing both alone roughly halves your output.
With two people, one loads and runs the mixer continuously while the other barrows, spreads and screeds. Batches arrive at a steady rate and the pour progresses evenly.
Alone, you load a batch, wait, tip it, barrow it, place it, then walk back and start again. The mixer stands idle for half the cycle, and the concrete already placed is setting while you are away from it.
For anything over about 0.3m³, find a second pair of hands. It is the single biggest improvement you can make to a hand-mixed pour.
Cleaning the drum
Clean it the same day, without exception. Hardened concrete in a drum is extremely difficult to remove and permanently reduces capacity.
Put a few shovels of clean coarse aggregate and some water in the drum and run it for five minutes. The stones scour the sides. Tip it out, rinse, and leave the drum tilted down so it drains.
Hose the outside, the frame and the wheels too. Cement that dries on the frame is there for good.
Cold and hot weather
Below about 5°C, use warm mixing water and keep bags of cement somewhere frost-free. Below 2°C, hydration effectively stops and a frozen batch is permanently damaged.
Above about 25°C, batches stiffen noticeably faster. Mix smaller quantities, use cold water, and keep the aggregate pile shaded. Resist the urge to add water to a stiffening batch — discard it and mix a fresh one instead.
Safety
Wet cement is caustic and causes chemical burns that develop slowly — people often do not notice until the damage is done. Wear waterproof gloves, long sleeves and eye protection, and wash any splashes off immediately.
Dry cement dust is a respiratory irritant and contains crystalline silica. Wear a mask when tipping bags, and tip low into the drum rather than from height.
Never put a hand or a tool into a rotating drum.
Common questions
How much concrete does a mixer make in one batch?
About 0.05m³ from a standard 120 to 140 litre electric mixer — roughly a third of a barrow load. A large petrol mixer manages 0.08m³.
What order do you put things in a cement mixer?
Half the water, then aggregate, then cement, then sand, then the rest of the water. Dry cement into a dry drum cakes onto the blades and short-changes the mix.
How long should concrete be mixed?
Three to five minutes after the last water goes in. Under-mixed concrete has streaks of dry cement and inconsistent strength.
Can I leave concrete in the mixer overnight?
No. It will harden and be very difficult to remove. Clean the drum with aggregate and water the same day, every day.
Electric or petrol mixer?
Electric for domestic work near a power supply — quieter, lighter, cheaper to hire. Petrol where there is no power, or for larger batches on site.