Summerhouse Base overkill?

[andrewjames]

Hi All,

I'm in the process of digging out a 7.5m x 4.3m (32m2) plot to stand a concrete base for a summerhouse, the overall depth of the plot varies slightly from 150-250mm from where the garden slops in both directions

My plans are to make use of the piles of general hardcore and rubble i have to clear by filling the majority of the depth then to spread a number of bags of MOT Type 1 over the hardcore using a compactor to form a fairly level base, then to blind with sharp sand to fill in any voids on which to lay some DPM then pour the concrete in one go

Based on the above I would expect the actual depth of the concrete part to be anything from 75-100mm once i have a fairly compacted base

I have a few questions / concerns

Is my plan to fill the gaps with MOT and blind with sand a good idea when i could just fill the voids with cement, am i saving money on cement by doing this?

MOT = £40 per tonne, Cement - £120 m3

Do i need to add A142 steel reinforcement mesh with a fairly shallow concrete slab? its not a garage so minimal weight

Also is it wise to add a damp proof membrane between the compacted base and the slab, cutting this out would save me the costs of the sand and DPM

Thanks for any input

Andrew

p.s Mods please move to Building is this is more relevant thanks

 

[r896neo]

Be careful not to have a deep layer of hardcore followed by a layer of MOT as the mot will wash down into the gaps in the hardcore leaving voids. Ideally a single layer of hardcore arranged evenly so there are gaps between it all is a good method.

Your concrete should be at least 100mm thick and if your putting steel mesh in probably go for 125mm with the steel in the middle.

You don't need a proper grade dpm as its only there to stop your concrete drying out too quick. Any polythene in a large sheet will do.

You can also forget the sand as a puncture hole here and there doesn't matter for the same reason as above.

 

[andrewjames]

Be careful not to have a deep layer of hardcore followed by a layer of MOT as the mot will wash down into the gaps in the hardcore leaving voids. Ideally a single layer of hardcore arranged evenly so there are gaps between it all is a good method.

Your concrete should be at least 100mm thick and if your putting steel mesh in probably go for 125mm with the steel in the middle.

You don't need a proper grade dpm as its only there to stop your concrete drying out too quick. Any polythene in a large sheet will do.

You can also forget the sand as a puncture hole here and there doesn't matter for the same reason as above.

Thank you r896neo.