Concrete base for shed

[sucker69]

We are building a concrete base 4m x 4m as a base for a wooden shed at the end of the garden. We have dug 100mm and infilled with MOT type 1 which will be compacted.

Questions:
1. Is it necessary to lay DPM ?
2. Is it necessary to lay some sharp sand on top of the MOT type 1 and compact ?

Thereafter, I will lay 100mm concrete.

Thanks

[IanMelb]

(1) I did - it may not be necessary, but I'm going for as many belts and braces as I can - it'd be a lot more grief to replacea rotted wooden shed than it would to lay the DPM
(2) I didn't - by the time the type1 was compacted it was really flat, with no pointy bits. I suppose, going by my belt and braces approach then I should have done, but that seemed to be a little too much faff ...

Others may have a decent, professional opinion, mine is just my recent experience

[lutonlagerlout]

DPM is always a good idea for paths and bases as it stops the crete going off too quick and cracking
the sand blinding is purely to stop aggregate from the subbase making holes in the DPM
cheers LLL

[Tony McC]

1 - not necessary but recommended

2 - only if the Type 1 material has an open texture when compacted