I mixed my first concrete by hand in a plastic trough with a spade and no idea what I was doing. It was for a small fence post and I had bought a bag of "general purpose concrete mix" from a DIY store. I added water until it looked about right - which, with hindsight, was far too much - and poured it around the post.
The post is still there. But the concrete is quite pale and slightly crumbly looking at the surface, which is the classic sign of too much water. The water:cement ratio is one of the most important things about concrete, and "add water until it looks right" is not a good enough process.
Here is how to do it properly.
Mix ratios for common applications
The ratio describes the proportions of cement : sand : aggregate (or cement : all-in ballast). These are by volume.
| Application | Mix ratio | Using all-in ballast |
|---|---|---|
| General purpose concrete (shed bases, paths, fence posts) | 1:2:4 | 1:5 |
| Foundations and footings | 1:3:3 | 1:5 |
| Paving bedding mortar | 1:5 (cement:sharp sand) | - |
| Lean mix / blinding | 1:3:6 | 1:8 |
1:2:4 (1 part cement, 2 parts sharp sand, 4 parts 10-20mm coarse aggregate) is the standard general-purpose domestic concrete mix. Using all-in ballast simplifies this to 1 part cement to 5 parts ballast.
Using bagged pre-mixed concrete (which contains cement, sand and aggregate already blended) is simpler still - just add water.
The critical point about water
This is where most hand-mixed concrete goes wrong. Too much water:
- Weakens the concrete significantly (every extra litre of water per bag reduces strength)
- Causes the surface to bloom pale and chalky as excess water migrates up
- Increases shrinkage and cracking as the concrete dries
The correct consistency is stiff enough that if you pick up a handful and squeeze it, it holds its shape and leaves your hand slightly damp but not wet. It should slide slowly off a shovel, not pour off it.
A useful test: make a peak with your spade. The peak should hold its shape. If it slumps flat, the mix is too wet.
Water quantity as a guide: roughly 0.5 litres of water per kg of cement. For a 25kg bag of cement in a 1:5 mix with ballast, that is around 12-13 litres total. But always add water gradually and test the consistency - humidity in the aggregates and air temperature both affect how much water the mix needs.
Mixing method by hand
What you need:
- Mixing board or large plastic trough (a standard 90-litre builder's tub is ideal)
- Spade or large mixing paddle
- Measuring bucket for consistent proportions
- Water supply and a watering can (for controlled pouring)
Step 1: Measure out and mix the dry materials first. Add the aggregates to the trough, then the cement. Mix the dry materials thoroughly until there are no streaks of cement.
Step 2: Make a well in the centre of the dry mix. Pour about two thirds of your calculated water into the well.
Step 3: Work from the outside of the pile inward, folding and turning the mix over the water. Keep working until the water is absorbed.
Step 4: Check the consistency. Add more water in very small amounts if needed, mixing fully between additions. The correct consistency for most applications is firm but workable - not sloppy.
Step 5: Mix for at least 2-3 minutes after adding the last of the water. Under-mixing leaves dry lumps of cement in the concrete.
When to stop mixing by hand and hire a mixer
| Volume needed | My honest recommendation |
|---|---|
| Under 0.1 m3 (~8 bags) | Hand mixing reasonable |
| 0.1-0.2 m3 (8-17 bags) | Consider a mixer |
| Over 0.2 m3 (17+ bags) | Hire a mixer |
| Over 0.5 m3 | Consider ready-mix |
A small electric or petrol mixer makes mixing significantly easier, produces more consistent results, and handles batches continuously without physical exhaustion. Hire centres typically charge £30-50 per day for a small mixer (100-120 litre drum) - that is good value for anything other than the smallest jobs.
Mixing 20+ bags by hand is genuinely exhausting and the consistency of later batches suffers as fatigue sets in.
Working time and temperature effects
Once mixed, concrete begins to stiffen. Working time depends on:
- Standard concrete in normal conditions: 30-45 minutes
- Hot weather (over 25C): 20-30 minutes - work faster or use fewer admixtures
- Cold weather (under 5C): Do not pour concrete if freezing conditions are forecast within 24 hours. Concrete gains strength very slowly below 5C and not at all below 0C. Frost in fresh concrete can ruin it.
Mix only what you can pour and level within your working time. Trying to re-work stiffening concrete is a waste of time and the result will be weaker.
My tips for hand mixing
After mixing concrete in a trough, in a mixer, and once memorably in a wheelbarrow in the rain:
Never add the water all at once. Add in thirds, mixing thoroughly between additions. The consistency of the last third of water is where you fine-tune to the right workability.
Use a consistent measuring system. If your mix ratio is 1:5 and you are using a bucket to measure, be consistent - the same bucket for every measurement. Eyeballing proportions leads to variable concrete.
Wear gloves. Fresh concrete contains calcium hydroxide which is strongly alkaline. Extended skin contact causes chemical burns that look like nothing at first but hurt a lot later. Cement burns are a well-known occupational hazard.
Clean your tools as you go. Concrete setting on a spade or mixing trough is much harder to remove than fresh concrete. Keep a bucket of water nearby and dip tools between batches.
For working out how much concrete your project needs before you start mixing, use the Concrete Base Calculator.