When concrete is used in driveways and pathways, it is laid in a frame called the formwork. It is into this frame that wet concrete is poured until the concrete hardens. The formwork, like a mould, is used to control the shape, position, and alignment of the wet concrete until hardened. Depending on the strength required, the formwork is reinforced with gravel and steel of varying density and patterns dictated by civil engineering principles.
When you are preparing the surface, a lot is dependent on what the concrete will be needed for. However, you should not lay it when the weather is very cold as the frost could damage the concrete.
The area should be measured and marked where the concrete needs to be put. The corners should have 90 degree angle.
The bushes and branches which are within 300 mm should be cut and cleared.
The turf needs to be cut and excavated to the specified depth as per the instructions of the manufacturer. Usually the depth should at least be 100mm. The bottom of the area which is excavated needs to be compacted.
When curving concrete needs to be done garden hosepipe or long rope should outline the curve. To produce the curve with timber, you need to cut half of the depth on the side which is inside of the curve. The cuts should be made 125 mm away or closer.
When you want to pour the concrete, first a sub base is needed. This consists of gravel and sand but you need to can alternatively also use crushed brick so that it is easy to compact. The depth of the sub based is dependent on the weight of what will rest on the concrete. Minimum 100 mm should be there.
When you mix concrete, it should be done close to the formwork and protective gloves are needed as concrete burns could happen when the skin is in contact with it. When mixing, it is 1 part of cement to 2 parts of sand and 3 parts of stone particles.
When laying the concrete, you should first dampen the sub base surface with water. Then the concrete should be poured starting at one end of the form. The concrete should fill the corners of the form too. The mixing and pouring should continue till the concrete is at least 12mm above the height of the form.
The concrete then needs to be smoothened and compacted using a tamping beam which has a straight edge. For this a timber plank will do – one which is longer than the form width. You should start at one end and tamp till the other. Gradually you should go down across the surface. Excess concrete can be removed by tamping in a forward and backwards motion. To prevent the concrete from drying out, it should be covered with polythene sheets which are weighted down.
The concrete should be cured for at least 3 days before the cover can be removed and after another day, the formwork can be removed.
When concrete is laid in large areas, it should be laid in sections so that it does not crack when it contracts or expands. This can be done by dividing the formwork into various bays.
When concrete needs to be finished well, the bull float needs to be moved across the slab in a direction perpendicular to the leveling board. Alternatively a Darby can be used. This needs to be moved back and forth till the surface has been done twice. The corner should be tidied using a smaller tool using a back and forth motion.
Grooves should be cut in the joints in distance not exceeding 24 times the thickness.
The concrete needs to be finished using magnesium or aluminum floats. People can also trowel or use a broom finish if they want a non slip surface.
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