The Brew Cabin

I'm about to build a base for a summerhouse (c. 4x5m, 1500kg).

I'm planning to use 60x60cm paving slabs recovered from our old patio. I think they are c 35mm thick.

Sub grade is garden soil (clay).
Should I try to compact this after excavation (is it worth the effort) ?

I was planning to put down a subase of scalpings (I have tried to get MOT 1 but all the local BM's are offering is 'scalpings').

How thick before/after compation should this be for this application (summerhouse base)?

I was then planning to lay the slabs on 50mm wet mortar (full base - I wouldn't dare consider 5 spots having looked around your site!). But it sounds like you would prefer a 10:1 sharp sand /cement dry mix
(also 50mm? after compaction?) with a wet mortar infill.

Could you confirm please what is best in this case?

Many Thanks!

A sub-base isn't really essential for this type of project, but it's handy if you need to level off the clay when you've dug out for the paved hard-standing. If you aim for 75-100mm of 'scalpings', that will be fine. Running the vib plate over the 'scalpings will be enough to consolidate any loosened spots in the clay. Running a vib plate over fresh clay is not a brilliant idea as they tend to get stuck and they can be a right bugger to loosen! Besides, you end up with loads of sticky clay smeared over the base plate.

You can bed the flags on a wet mortar if you prefer - again, 50mm is plenty and although a 10:1 mix is adequate, you can increase that to a 8:1 or even a 6:1 if you really want to. The idea behind using a cement-bound bed isn't so much to make a rock-hard, super-strong base, but to bind the sands together so they don't drift or settle too much.

As most of the flags will be beneath the planned summerhouse, there's no real need to point the joints. It's not as though any weeds would stand much of a chance growing under there with little or no light, but again, if that's what you want to do, there's nowt wrong in so doing.