How To (DIY Projects)

A General Guide for Do-It-Yourself Cement Projects

Concrete is one of the most versatile and easy-to-use building materials available anywhere in the world. The guidelines in this page can help builders and DIY enthusiasts make their own concrete and make their building projects a huge success.

Choose the right materials
To make a quality concrete, use quality materials available:
  • High quality National Cement products, which bears the CES 28 mark from Ethiopian Conformity Assessment Enterprise (ECAE), with the strength grade and certificate number.
  • Clean coarse sand, free of leaves, grass, twigs or other foreign matter. Sand should be fairly coarse, with particle sizes ranging from fine dust up to about 5 mm.
  • Clean stone with sizes in the range of 26.5 mm to 9.5 mm. Stone sizes of 26.5 mm can be used for thick sections such as foundations, deep suspended slabs and industrial floors thicker than 120 mm. 19 mm 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, precast items such as lintels, flagstones and other items with section thicknesses ranging from 40 mm to 50 mm.
  • Clean potable water.

Determine the Right Quantity of Concrete

When building projects, you might want to calculate the right quantity of concrete you have to prepare in order to avoid wastage of reources.

The calculation for the volume of concrete required to fill a square of rectangular section is: Width X Length X Width.

For a circular section, to calculate the volume of concrete required, use the formula: (Diameter^2) X 0.8 X Height

Thickness of Concrete

Structural concrete sections for any project are designed for specific thicknesses. For unreinforced concrete elements, the typical thickness are given in the table below.

Concrete Strength
Concrete strength depends mainly on the mix quantity proportion of materials used. Typically, concrete strength depends on the following factors:
  • The type and amount of cement
  • The amount of water
  • The type of sand
  • The type of aggregate
  • Effective curing
Note that adding too much water reduces the concrete strength.

Preparing Area Before Pouring Concrete

Before pouring concrete into foundations, make sure that the trenches are damp but with no standing water. This will place the concrete in a self-curing environment with three sides prevented from drying out by the soil. The sub-base for foundations, surface beds and ground slabs should be well compacted.

Ensure that the formwork is clean and adequately supported to retain the mass of the concrete.

Make sure that the steel reinforcing is adequately secured to ensure that it does not move while placing the concrete.

Mixing Concrete Manually
Concrete should be mixed on a flat, clean, and hard surface such as a concrete slab or steel sheet.
  • Spread the sand in a layer about 100 mm thick and then spread the cement on top, mixing the two thoroughly together until they form an even colour.
  • Pile the mixture into a heap and make a hollow in the middle.
  • Pour in water slowly in small quantities and mix until a smooth paste is formed. Too much water will produce a weak concrete. Too little will make the mix difficult to place properly.
  • Add the correct amount of stone and mix until every stone particle is coated. If the mix becomes too stiff to place easily, add a little more water and mix it thoroughly.

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