Concrete shed base questions


Hi All,
I am laying down a concrete base for my 16' x 10' timber shed / workshop.
I have dug down 5 inches below ground level and am planning to lay:
4 inches of compacted hardcore A layer of sand Damp proof membrane Then 4 inches of concrete (so the concrete should finish about 3 inches above ground level.)
I have a few questions which I would be grateful if anyone can answer:-
1) Should I lay the form board / shuttering down before I lay the hardcore? (This means boards need to be about 8 inches high). Or should I lay the hardcore first, then 4 inch high boards (nailed to stakes driven into the ground). I am worried that if I put the boards down first, they may split when compacting the hard core with a whacker plate. 2) Is a 19mm thick board ok to use (for the shuttering) 3) What do I do with the damp proof membrane after the concrete has set - should I just cut the edge of it flush with the concrete?
Any help would be appreciated! Thanks, Rob
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Yes, this second way.

As long as you have enough pegs to nail it to. Make sure there is not too much (or any) 'give' between pegs.

If the concrete is below gound level, then cutting the DP membrane below ground will render it ineffective. You'll need to fold it up and make sure when you cut it of that all of the cut edge is above ground. Also, you'll need to ensure that moisture or rain does not enter between the DPC and the concrete. Personally, I'd either not worry too much about a DPC, or put it on top of the concrete, under the shed timbers. At least it will be above ground.
Rob Graham
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You haven't said if the shed will have its own floor or will have the concrete base as the floor.
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Sorry - the shed has a T&G floor - but there are timber bearers underneath it (so T&G won't sit directly on concrete base).
Rob
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I'd settle for giving the bearers an extra dose of preservative.
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