Its half art and half science and yes we do tend to overdo things.
Getting back to your original post you have the slabs so the assumption is you will want to use these.
The question is the depth you want to lay them at / how much soil you want (need) to remove. Key criteria is to lay them level and for them to remain stable.
Digging a deeper base reduces any likelihood of frost heave and hardcore / sub-base improves drainage and spreads out any concentrated surface loads evenly over the subgrade. In your case for a simple shed not an issue. If your shed base were to settle unevenly by say 10mm you probably wouldnt notice and the typical shed would settle without damage. Shrinkage of the timber components of the shed are likely to be a bigger issue.
Any bedding (such as sand or mortar) although not essential will make it easier to lay the slabs. It will act as a regulating layer between the ground and the slabs – takes out any irregularities between the ground and the underside of the slabs. The thickness required will depend upon how level you can make the ground beneath the slabs so the slabs neither sit on hard spots or span voids. Ideally, they should be in full contact with the bedding. So long as your ground is level a nominal 10 – 15mm layer should suffice (say 4 – 5 of the small Wickes / B&Q bags over a 2m x 2m area). Use a straight edge to rule the sand to a level surface upon which the slabs can be laid.
In days gone by paving slabs (for pavements) were laid on a weak lime mortar mix and tamped to their desired level but it does require a bit of skill and I expect you will be more successful by levelling a sand base with a straight edge and laying the slabs on top.
As I said in the earlier post if your ground is bad you may wish to dig out a bit more or compact it a bit more but in reality unless you have very bad ground, it wont matter.
Some folks have mentioned using timber as a base and this will work for a while – the same analogy for using wooden or concrete fence posts. Moisture destroys wood so if you intend to keep the shed for a long time ensure the wooden base is separated from ground moisture.
Getting back to your original post you have the slabs so the assumption is you will want to use these.
The question is the depth you want to lay them at / how much soil you want (need) to remove. Key criteria is to lay them level and for them to remain stable.
Digging a deeper base reduces any likelihood of frost heave and hardcore / sub-base improves drainage and spreads out any concentrated surface loads evenly over the subgrade. In your case for a simple shed not an issue. If your shed base were to settle unevenly by say 10mm you probably wouldnt notice and the typical shed would settle without damage. Shrinkage of the timber components of the shed are likely to be a bigger issue.
Any bedding (such as sand or mortar) although not essential will make it easier to lay the slabs. It will act as a regulating layer between the ground and the slabs – takes out any irregularities between the ground and the underside of the slabs. The thickness required will depend upon how level you can make the ground beneath the slabs so the slabs neither sit on hard spots or span voids. Ideally, they should be in full contact with the bedding. So long as your ground is level a nominal 10 – 15mm layer should suffice (say 4 – 5 of the small Wickes / B&Q bags over a 2m x 2m area). Use a straight edge to rule the sand to a level surface upon which the slabs can be laid.
In days gone by paving slabs (for pavements) were laid on a weak lime mortar mix and tamped to their desired level but it does require a bit of skill and I expect you will be more successful by levelling a sand base with a straight edge and laying the slabs on top.
As I said in the earlier post if your ground is bad you may wish to dig out a bit more or compact it a bit more but in reality unless you have very bad ground, it wont matter.
Some folks have mentioned using timber as a base and this will work for a while – the same analogy for using wooden or concrete fence posts. Moisture destroys wood so if you intend to keep the shed for a long time ensure the wooden base is separated from ground moisture.
