Build a concrete base
Make sure the design is suited to the garden building purchased, if you having any doubt please ask us when purchasing the garden shed.
Concrete is a mix of All in Ballast, Cement and water for the type of base these are mixed to a ratio of which:
- 1 part Cement
- 5 parts All in Ballast
- All in Ballast is usually sold in 40kg bags from your local hardware store such as B&Q and Home base.
Shed base = 8' wide x 6' long x 3" depth
Volume = 8' x 6' x 0.25 which equals to 12 cu ft
Add 1/3 for compacting = 4 cu ft
All in Ballast which is required is = 16 cu ft
All other garden shed bases can be worked out using the same principal, there is a good rule to follow and that would be to order in generous sizes, therefore unforeseen circumstances can be solved quickly.
1 bag of cement mixed with the All in ballast with the ratio of 1:5, makes 24 sq.ft of concrete equalling a 3" base
18 sq.ft with a 4" base.
Calculations are based on an 8 x 6 garden shed / garden building.
3" base requires 2 bags of cement .
4" base requires 3 bags of cement
Quantities for other size bases may be worked out using these figures.
The Tools required for the Job
- Tape Measure and string (for the Guide lines)
- Spirit Level
- Set Square
- A Cement Mixer for the big jobs
- Levelling Beam
- Wooden / Plastic Float
Make sure any over hanging trees and bushes are cut back to allow at least a good 12" around the actual base, the base must be firm, level and designed to situate the floor of the selected garden shed.
Carefully marking out the exact size of the garden shed base, maybe best making the actual size 1" bigger to alloy for shrinkage or the shed size. Using wooden pegs and string, mark out the base then measuring the diagonals, if these are the same then its square. After the base is cleared and dug out level and compact the ground.
For a general garden shed a 3" bed is sufficient in most situations on soft clay. For larger buildings, making the thickness of the base 4" and laid on a finely chopped hard-core bed. Half the depth of the base should be above ground level.
Now replace the string back onto the pegs and again check the measurements, the string is used for the position of the frame, which is made from 2" timber (please make sure the depth is the same as your base).
Using a spirit level and a set square to set the frame accurately, once this is done the frame will require to be nailed / screwed to the pegs. A very important note to remember. make sure the pegs do not protrude the top of the frame as it will make levelling a task.
Mix the concrete
If possible mix the concrete alongside the base, this makes placement of the concrete far easier, if this is not possible a wheel barrow will be needed, using a plastic bucket (3 Gallon Bucket) for measuring the materials and use a separate bucket for measuring the water.
Mix well in the proportion
1 bucket of Cement
5 buckets of All in Ballast 20mm
Adding the water gradually to the mix until the whole pile if uniform in colour and sufficiently workable to use, Do not make the mix too wet, this will weaken the concrete. make a note on how much concrete has been used and use the same for each mix there after.
Placement of the concrete
Place a layer of concrete into the frame and compact this down with a Rammer take care to push the concrete into the corners and edges. tap the sides of the frame with a Hammer to help produce a solid edge to the slab.
Continue to place layers of concrete into the frame compact until full and ready for levelling.
Use the levelling beam with a chopping and sawing motion across the top of the slab, working from side to side and one end to other will level off the top leaving it flush with the frame. once level smooth the top off with either a plastic or wooden float.
Concrete must not be permitted to dry out too quickly or be damaged by frost whilst it is wet. Cover with plastic sheeting until the concrete is solid, spray with water for several days to allow it to dry out slowly.
When the base is ready remove all the frame and sheeting, tidy round the edges and wait for the arrival of the new garden shed.
All in Ballast info:
Known as combined or all-in aggregate, this is a mix of sharp sand and coarse aggregate and is used for making concrete. The proportions of sand to gravel are not normally guaranteed but are acceptable for use in a general purpose concrete mix.