Garage foundations and slab ? - Require some guidance as how to continue

[bonzaozzy]

Hi I am looking to dig foundations for a 8x4m garage and require some info on how best to prodeed.
Using 440x215*200 blocks I was planning to dig and fill foundations 0.45 wide to a depth of 0.4m, this brings me down into the subsoil hard base. Then start block work from here and build up from there about 2 courses, install the Damp Course 0.15m above intended floor level, and then flood the internal area with concrete to create the slab floor(May use rebar over this area). Will it be ok to dig the slab area out to a depth of approx 0.3m then fill a subbase of 0.15m, and then concrete of 0.15m onto this? My concern is that the subase will be going onto a layer of topsoil, as there would be a huge amount of infill if I was to dig the whole area down to subsoil.
I look forward to your suggestions.

[Tony McC]

The only fault I can spot in your plan is the omission of a dpc between concrete slab and sub-base. An 8x4 slab will need at least one crack control joint, and I'd recommend placing a compressible filler against the masonry to act as an expansion joint and relieve presure on the masonry, but everything else sounds fine.

[bonzaozzy]

Many Thanks for your response.
Yup was going to use a DPC under the main floor base, I will look into crompressable joint material for between the floor and masonary.
The Joint should that be so the floor ends up as 2 ... 4mx4m slabs ? How do I create this joint when laying ready mix concrete from a delivery by truck? I was thinking of cutting the joint with a sthil saw but would then cut through my DPC.
What happens with the re-bar sheet I will have layed across the floor?

Cheers

[Tony McC]

Pour as a single slab and then cut a control joint 24-48 hours later. You only need to cut to 25-40mm depth, not all the way through, and don't forget to seal it with Thioflex or similar to protect any steel rebar.