Concrete Mixing Hints

Mix ratios

The correct mix ratio (cement:sand:stone) depends on the type of application; harder concrete requires more cement, rougher applications require more aggregate. The ratios given below are guidelines: best proportions may depend on the quality of sand/stone used.

First put in the water - around 7 litres (1½ gallons), using more or less depending on the type of mix required. Add some aggregate before adding cement, to avoid sticking. Work consistently to the ratio of ingredients for whatever type of concrete mix you are working to.

	Mix	Batch quantities			Approx batch output (ltr)
	Mix	Cement (50kg bag)	Sand (ltr)	Stone (ltr)	Approx batch output (ltr)
Most ordinary concrete	1:2:4	½ bag	35	70	85
Foundations	1:3:6	¹/3 bag	35	70	78
Rough mass concrete	1:4:8	¼ bag	35	70	78
Watertight floors, tanks, pits, etc	1:1½:3	²/3 bag	35	70	85
for 35 litres use approx 6 No 2 shovels; 1m³ = 1,000 litres

Getting a good mix

The approximate mixing time for concrete is 2-4 minutes from when all the material (including the water) has been added - over-mixing can reduce strength and cause segregation of the coarser aggregates.

Beware of low grade aggregates; these will only lead to trouble later on with sinking and frost spoiling the appearance of the pour.

Also do not get the concrete mix too wet as this can reduce strength and make it less able to withstand weathering.

Looking after your mixer

Never throw material into the mixer - trickle it steadily over the rim or it will stick firmly to the back of the drum and can only be dislodged by stopping the mixer.

Keep your mixer clean - material left in the drum will harden, and attract more on each use until the mixer is useless.

Do not throw bricks into a mixer drum to clean it out. The best method is a mix of 1" (2½cm) gravel and clean water - use plenty of it, as this will do the job in half the time.

Mixer capacities

Old systems of description are still very much in use. This chart provides a comparison of the frequently used terminology.

	Minimix 150	Maxi	Premier XT
	Minimix 150	Maxi	100	150	175	200
Cubic feet	4:3	4:3	5:3½	7:5	8:6	10:7
Litres	120:90	120:90	160:110	220:160	250:180	310:220
Bag (1cwt)	½	½	¾	1	1¼	1½
Bag (25kg)	2	2	3	4	4½	5
Barrow	1	1	1½	2	2¼	2½
Cubic feet and litres are a ratio of – Input (dry material) : Output (wet mix)
Bag refers to the input quantity of cement
Barrow refers to the output volume measured in wheelbarrow loads

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