Batching by volume - DIY

The strength of concrete varies with constituent proportions. When concrete is to be mixed on site rather than ordered from a concrete supplier, an estimate of the materials needed is necessary. Materials can be purchased as individual constituents with either the fine and coarse aggregate pre-blended (ballast/all-in aggregate) or separately.The quantities of cement, sand and coarse aggregate or cement and ´all-in aggregate´ for various concrete volumes are estimated in the Table below. The bags of cement are assumed to be 25kg and the largest size aggregate is assumed to be of nominal size 20mm.

Mix	Use	Materials	Separate	All in	Quantity per m3
Foundations	Footings, blinding, fence posts	Cement Sharp Sand Coarse aggregate All in aggregate Water*	1 2.5 3.5	1 6	5 bags 500 kg 800 kg 1300 kg 100 litres
General use	Garage, shed base & domestic floors	Cement Sharp Sand Coarse aggregate All in aggregate Water*	1 2 3	1 5	6 bags 450 kg 850 kg 1300 kg 100 litres
Paving	Paths, drives & steps	Cement Sharp Sand Coarse aggregate All in aggregate Water*	1 1.5 2.5	1 4	8 bags 400 kg 800 kg 1200 kg 100 litres
Bedding mortar	For paving slabs	Cement Sharp Sand Water*	1 4		8 bags 1000 kg 130 litres

* Water should be added to obtain a workable but non-segregating mix, the total free water being roughly 170 litres per cubic metre of concrete, and 203 litres per cubic metre for bedding mortar. The water figures in the table for 1m³ have been adjusted to account for water in the aggregate.

The table is for batching by volume. A suitable gauge box or similar is therefore needed. A simple method is to use bucket, based on 1 bucket of cement. For a 1:2:3 general use mix it will be 1 bucket of cement with 2 buckets of sharp sand and 3 buckets of coarse aggregate, alternatively 5 buckets of all-in aggregate. The figures assume a general bulking factor for the materials and do not take into account any water in the sand or aggregate.

Please note: Use a separate shovel and bucket for the cement so that they do not get damp causing lumps in the cement or bucket.

See additional entries below for mixing small quantities by small hired concrete mixer or by hand. Another option is to use pre-batched bags of materials form builders merchants and just add water.

Concrete Bookshop - Members receive 40% discount on Concrete Society publications