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Your guide to Concreting with Ohorongo Cement

Your guide to concreting
Your guide to concreting
Materials

Cement

Use CEM II B-LL 32.5N cement or CEM II A-LL 42.5N cement, depending on the purpose and function of the concrete.

Aggregates: Sand & Stone:

  • Coarse sand (particle sizes ranging from fine dust up to 5 mm in size);
  • Stone(particle sizes 19 mm, 13.2 mm or 9,5 mm - depending on the purpose and function of the concrete).

NOTE: 19 mm size stone can be used for floors, paths, patios and driveways. Stone sizes of 13.2 mm or 9.5 mm can be used for thin concrete sections such as thin suspended slabs and precast items such as lintels.

Water

Use clean, drinkable water.

Calculate the right quantity of concrete
Calculate the right quantity of concrete
Mixing Concrete

When mixing concrete, always consider the final purpose of the concrete and choose the appropriate proportions. Refer to the section overleaf for the correct mix proportions, as it is important to mix the concrete in exact accordance with these specifications.

Machine mixing is preferable to hand mixing. However, if the concrete is mixed by hand, special care should be taken to follow these instructions:

  • Ensure you have the correct proportions of cement aggregate and water at hand;
  • Mix the concrete on a clean, hard surface such as a concrete floor or steel sheet;
  • Spread the sand in a 10 cm thick layer on the floor or sheet; Spread the cement uniformly over the sand;
  • Blend until the cement and sand mixture are of a uniform colour;
  • Add the correct amount of stone and blend the mixture until every stone particle is coated.
  • Pile the mixture into a heap and make a hole in the middle;
  • Add the required amount of clean water in small quantities, blending after each addition until a smooth paste is formed. Too much water will produce weak concrete. Too little will reduce workability and make casting difficult.
  • Ideally, the time between the preparation of a batch of concrete and when that batch is placed and compacted should not exceed 90 minutes. Should the concrete not be placed immediately after batching, cover it with plastic sheets or wet sacking, so that it does not dry out in the sun or wind.

Warning: If the concrete has hardened and is not workable anymore, that batch of concrete has to be discarded. Do not attempt to mix additional water into the concrete mixture, as this reduces the strength result of the mixture. At any one time, only prepare the amount of concrete that can be used up before the mixture dries out.

Proposed Mixed Proportions
CEM II/B-LL 32.5 N OHORONGO CEMENT SAND STONE VOLUME M3
HIGH STRENGTH
High strength and watertight concrete, driveways and carports
1 1 1 0.1 m3
MEDIUM STRENGTH
Concrete floors, patios, footpaths, etc.
1 1 1/2 1 1/2 0.14 m3
LOW STRENGTH
Concrete foundations and footings
1 2 2 0.18 m3
EXTERIOR / DRY MORTAR AND PLASTER
mortar and plaster exposed to dampness -
mix designs are based on the use of good quality sand
1 2 - 0.1 m3
INTERIOR / DRY MORTAR AND PLASTER
Mortar and plaster not exposed to dampness -
mix designs are based on the use of good quality sand
1 3 - 0.14 m3

The volume of the wheelbarrow is 60 litres
 

CEM II/A-LL 42.5 N OHORONGO CEMENT SAND STONE VOLUME M3
HIGH STRENGTH
High strength and watertight concrete, driveways and carports
1 1 1/2 1 1/2 0.14 m3
MEDIUM STRENGTH
Concrete floors, patios, footpaths, etc.
1 2 2 0.18 m3
LOW STRENGTH
Concrete foundations and footings
1 2 1/2 2 1/2 0.21 m3
EXTERIOR / DRY MORTAR AND PLASTER
mortar and plaster exposed to dampness -
mix designs are based on the use of good quality sand
1 2 - 0.1 m3
INTERIOR / DRY MORTAR AND PLASTER
Mortar and plaster not exposed to dampness -
mix designs are based on the use of good quality sand
1 3 - 0.14 m3

The volume of the wheelbarrow is 60 litres

General Remarks on the use of Cement

The properties and quality of concrete, mortar- and plaster mixes, in both fresh and hardened states, largely depends on the properties of the materials used.

All aggregates (sand and/ or stone) should be clean and dry and not contain clay or organic matter such as leaves, roots or humus.

Always store cement and aggregates in a dry place. To avoid moisture rising from the ground, place cement bags on plastic sheeting or a raised wooden platform and cover when necessary to protect against the weather.

Categories: Guides

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