Perhaps you want to add an addition to your home or build a garage and you wish to lay a concrete foundation. Apart from standard materials you will probably need to hire day labourers or rope in family and friends to complete this task. Make sure you are physically fit before exerting yourself building a concrete foundation.
Determine how think the slab will be. This will be determined by the use and size.
Excavate or dig down twice the thickness of the slab. If the concrete foundation is going to be 7.5 cm (3 inches), then you need to go down 15 cm (6 inches).
Remove any large stones or garbage from the area you excavated, then rent a compactor and compact the ground.
Put down sand or gravel or something for drainage so water will not come up through the slab.
Lay down a vapor barrier, especially if the concrete foundation is going to be used for interior use such as a house.
Build a wood frame to lay a concrete foundation. Make screed rails from 5 by 10 cm (2 by 4 inch) boards and put them on opposite sides around the outside of the foundation. Span the screed rails with a straightedge. This slides across the rails, removing excess concrete and helping to make the concrete level.
Pour the concrete for the foundation and allow the straightedge to slide, leveling the concrete as it goes. Once the concrete is firm enough, remove the straightedge and rails.
Finish the concrete foundation you are laying with hand or power trowels. Remove any imperfections the straightedge has left, then let the concrete foundation sit and cure.