Requiring significantly smaller volumes of concrete does not necessarily require mixing equipment.
Concrete can be mixed by hand and get a very good quality, comparable to that produced in concrete mixing plants, provided certain recommendations are followed.
For example, in a concrete mixture, Portland cement and water form a paste, that endurarse, binds particles of sand and gravel.
Using a lot of mixing water to produce concrete dilutes the pasta, weakening the qualities of cement. Therefore, it is important that the Portland cement and water are used in the right proportions for best results. The following table provides the recommended amounts for mixing depending on the type of work performed.
Preparation f'c 100kg / cm2:
1 sack of cement - 6 ½ buckets of sand - gravel size boats 7 ¾ - 2 bottles of water
This preparation is used for curbs, sidewalks and firm.
Preparing f'c 150kg / cm2:
1 sack of cement - 5 buckets of sand - gravel size 6 ¾ boats - 2 bottles of water
This preparation is used for floors, chains and castles.
Preparing f'c 200kg / cm2:
1 sack of cement - 4 jars of sand - gravel 5 boats size ¾ - 1 ½ water boats
This dosage used in slabs, beams, footings, foundation slabs.

Among other rules for the correct concrete mix we are:

'The water to be used for mixing concrete should be clean, usually the water you can drink, is good for making concrete.

-Remember Sand and gravel should not be measured in spades or carretilladas as they always are filled with different amounts; should be used to measure the same container.

-the concrete is made from a mixture of ¾ of sand and gravel and one quarter of water and cement. (75% sand and 25% gravel and cement and water).

-The Mixtures should not be contaminated with dirt, so we have to prepare them on a clean surface, preferably on a wooden platform. Aggregates (sand and gravel) also should be clean, free of dirt, clay, wood, roots or other material or vegetable or animal waste. Dirty room were washed with water and dried in the sun.

-Remember Before making any mixture need to know the resistance (f 'c) of concrete per square centimeter.

He must respect the proportioning indicated to perform the concrete mix, because if too much water is used, the resistance is less and if too much cement is used, the strength is ample and is more expensive. Thus the correct dosage in the concrete mix is ​​the key to quality.