The basic mix ratio for concrete is one part water, two parts cement and three parts sand. An alternative ratio is one part cement, two parts sand and three parts gravel with enough water added until the mixtures reaches the consistency of thick mud. Lime is also a common additive to the mix.
Concrete and mortar can be made from a mixture of masonry sand and either Portland cement or masonry cement. The addition of hydrated lime makes the concrete more plastic-like when it's wet and stronger and more durable after the concrete hardens. Masonry cement comes with lime already included.
For custom cement and mortar recipes, which result in concrete and mortar of varying strengths, Portland and masonry cement are measured by the bag. A 94-pound bag is standard. Lime comes in 50-pound bags. Masonry sand is usually sold loose and delivered by a truck, and it's measured by the mounded shovelful.
The cement or mortar is mixed by first adding a portion of the water. The sand and cement are then poured into the water, and the mixture is stirred for several minutes. More water, cement or sand can be added if the mixture is too wet or dry.
Below is an example of a sand to cement mix ratio recommendation from a cement manufacturer.
- Concrete - 1 part cement, 2 parts concreting sand and 3 parts 20 millimeter aggregate.
- Mortar - 1 part cement, 4 to 5 parts building sand. Alternatively, one can also use 1 part cement, 1 part lime and 4 to 5 parts building sand.
- Screed - 1 part cement and 3 to 5 concreting sand.
- Plaster/Render - 1 part cement and3 parts plastering sand, or 1 part cement, 1 part lime and 3 parts plastering sand.