How we recommend to build Concrete Bases - i.e. for Garden Buildings & Sheds etc. To the exact base size add 1" (25mm) to length and width - using these dimensions to set out the base. Mark 6" all around the outside of the prepared area for the overall size of the 'dig'. Check it is square by using pegs and string to confirm that the diagonals mark out the exact size of the required shed base. Remove the setting out strings but leave the pegs in place for further use.
Remove all vegetation and clear the topsoil to the depth required. Carefully level and compact the ground. On ordinary ground and for ordinary garden sheds, a thickness of 3" (75mm) is sufficient in most situations. On soft clay, or for larger buildings, increase the thickness to 4" (100mm) laid on 2" (50mm) of finely broken and compacted hard-core. On larger buildings, increase the thickness to 6” (150mm) laid on 3” (75mm) of finely broken and compacted hard-core.
N.B. At least half the depth of the base (approx) should be above ground level.
Replace the setting out strings on the pegs and check the original measurements. These strings are used for positioning the concrete formwork. This is made from 1" (25mm) thick timber and should be as wide as the depth of the concrete slab. Check the markings are still square by checking the diagonals again.
Use a tape measure, spirit-level and try-square to set off the formwork accurately. This is nailed onto pegs driven into the ground. These pegs should be sited on the outside of the formwork in each corner and every 2' (600mm). It is very important that the pegs do not protrude above the top of the formwork as this will make the levelling off the concrete very difficult. Ensure the top of the formwork is carefully checked and use a long spirit level to ensure it is level all round.
Concrete is a mixture of 'all -in' ballast, Portland cement and water. For this type of base, they are mixed to the ratio of 1 part cement to 5 parts 'all-in' ballast.
Concrete'Use All-in' ballast (10-20mm), Ordinary Portland Cement and water.
Example RequirementsShed base = 8' long x 6' wide x 3" deep
Volume = 8' x 6' x 0.25' = 12 cubic ft
Add 1/3 for compacting = 4 cubic ft concrete.
Add water gradually to the mix until the whole pile is uniform in colour and sufficiently workable to use. Do not make the mix too wet as this will weaken the concrete. Note how much water has been used and use the same quantity for each mix. A cement mixer is used for making large quantities of concrete.
Cement1 bag (50kg) of cement mixed with 'all-in' ballast in the ratio of 1:5 makes:
24 sq ft of concrete 3" thick or 18 sq ft of concrete 4" thick. ie
3" thick base cement = 2 bags for a 8' x 6' base (48 sq ft)
4" thick base cement = 3 bags for a 8' x 6' base (48 sq ft)
Quantities for other size bases may be worked out using these figures.
MixingTry to mix alongside the base site so that the concrete can be placed by shovel, otherwise use a wheelbarrow.
Mix well in the proportion of 1 bucket of cement to 5 buckets 'all-in' 10-20mm ballast.
Add water gradually to the mix until the whole pile is uniform in colour and sufficiently workable to use. Do not make the mix too wet as this will weaken the concrete. Note how much water has been used and use the same quantity for each mix.
Laying concretePlace a layer of concrete mic into the formwork. Compact this down with a rammer, taking particular care to push the concrete into the corners and edges.
Tap the sides of the formwork with a hammer to help produce a solid edge to the slab. Continue placing concrete into the formwork and compacting until full. Use a tamping beam with a chopping and sawing motion across the slab, working from one end to the other. This will level off the concrete, leaving it flush with the top of the formwork.
Tamp the concrete flat as it is poured. After tamping, smooth the concrete out with either a wooden or a plastic float to allow the batons of the floor to sit evenly. The concrete must not be allowed to dry out too quickly or be damaged by frost whilst wet. Use plastic sheeting to cover the concrete until it is hard and spray with water for several days to allow it to dry out slowly.
When the base is ready, remove the formwork and tidy around the base. Fill the 6" (150mm) around the edge of your new base with pea shingle to prevent 'splash-back' as rain drips to the floor.
Leigh Fencing & Landscaping can take no responsibility for the advice offered on this page. Before starting any DIY / Gardening project be aware of the 'Health & Safety' issues - if in doubt seek professional assistance.
If you need further advice with your purchase please ask our experienced staff, we will be happy to help!
Remove all vegetation and clear the topsoil to the depth required. Carefully level and compact the ground. On ordinary ground and for ordinary garden sheds, a thickness of 3" (75mm) is sufficient in most situations. On soft clay, or for larger buildings, increase the thickness to 4" (100mm) laid on 2" (50mm) of finely broken and compacted hard-core. On larger buildings, increase the thickness to 6” (150mm) laid on 3” (75mm) of finely broken and compacted hard-core.
N.B. At least half the depth of the base (approx) should be above ground level.
Replace the setting out strings on the pegs and check the original measurements. These strings are used for positioning the concrete formwork. This is made from 1" (25mm) thick timber and should be as wide as the depth of the concrete slab. Check the markings are still square by checking the diagonals again.
Use a tape measure, spirit-level and try-square to set off the formwork accurately. This is nailed onto pegs driven into the ground. These pegs should be sited on the outside of the formwork in each corner and every 2' (600mm). It is very important that the pegs do not protrude above the top of the formwork as this will make the levelling off the concrete very difficult. Ensure the top of the formwork is carefully checked and use a long spirit level to ensure it is level all round.
Concrete is a mixture of 'all -in' ballast, Portland cement and water. For this type of base, they are mixed to the ratio of 1 part cement to 5 parts 'all-in' ballast.
Concrete'Use All-in' ballast (10-20mm), Ordinary Portland Cement and water.
Example RequirementsShed base = 8' long x 6' wide x 3" deep
Volume = 8' x 6' x 0.25' = 12 cubic ft
Add 1/3 for compacting = 4 cubic ft concrete.
Add water gradually to the mix until the whole pile is uniform in colour and sufficiently workable to use. Do not make the mix too wet as this will weaken the concrete. Note how much water has been used and use the same quantity for each mix. A cement mixer is used for making large quantities of concrete.
Cement1 bag (50kg) of cement mixed with 'all-in' ballast in the ratio of 1:5 makes:
24 sq ft of concrete 3" thick or 18 sq ft of concrete 4" thick. ie
3" thick base cement = 2 bags for a 8' x 6' base (48 sq ft)
4" thick base cement = 3 bags for a 8' x 6' base (48 sq ft)
Quantities for other size bases may be worked out using these figures.
MixingTry to mix alongside the base site so that the concrete can be placed by shovel, otherwise use a wheelbarrow.
Mix well in the proportion of 1 bucket of cement to 5 buckets 'all-in' 10-20mm ballast.
Add water gradually to the mix until the whole pile is uniform in colour and sufficiently workable to use. Do not make the mix too wet as this will weaken the concrete. Note how much water has been used and use the same quantity for each mix.
Laying concretePlace a layer of concrete mic into the formwork. Compact this down with a rammer, taking particular care to push the concrete into the corners and edges.
Tap the sides of the formwork with a hammer to help produce a solid edge to the slab. Continue placing concrete into the formwork and compacting until full. Use a tamping beam with a chopping and sawing motion across the slab, working from one end to the other. This will level off the concrete, leaving it flush with the top of the formwork.
Tamp the concrete flat as it is poured. After tamping, smooth the concrete out with either a wooden or a plastic float to allow the batons of the floor to sit evenly. The concrete must not be allowed to dry out too quickly or be damaged by frost whilst wet. Use plastic sheeting to cover the concrete until it is hard and spray with water for several days to allow it to dry out slowly.
When the base is ready, remove the formwork and tidy around the base. Fill the 6" (150mm) around the edge of your new base with pea shingle to prevent 'splash-back' as rain drips to the floor.
Leigh Fencing & Landscaping can take no responsibility for the advice offered on this page. Before starting any DIY / Gardening project be aware of the 'Health & Safety' issues - if in doubt seek professional assistance.
If you need further advice with your purchase please ask our experienced staff, we will be happy to help!
