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That would work

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Hi
This is partly rhetorical but feel like discussing it.
About to start building new small workshop, 16x7 feet. Bit of a railway carriage!
It will pretty much be as Mike's drawing, three courses of bricks with 4x2 stud walls cladding, onduline roof so reasonably lightweight.
It will be going on top of a paved area, which has stone slabs on what I am pretty sure is a substantial concrete base.
I did think about going straight onto to the slabs with the three courses of bricks and leveling over the floor then using a liquid DPC before laying chipboard flooring but now I am now thinking to lay a concrete slab on the stone slabs, say 75mm thick and putting the brick base on that.
What are your thoughts guys?
 

MikeG.

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I'd lift the stones and see what is underneath. If they've been properly laid on a sub-base, with organic material removed, then fine, build on that if you must. I wouldn't personally, but that's your choice. If they are just laid on top-soil, as you usually find in gardens, then I certainly wouldn't build directly on the slabs. The biggest issue with a plinth laid directly onto a flat patio-type base is that will be a direct route through for damp, through the bottom bed of mortar, but of course, there are also the structural issues I've mentioned. Do it once, properly, and you won't regret it.
 

That would work

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Yes fair comment, the slabs are on a large raised staged area and are certainly on a lot of hardcore and good layer of concrete but yes Im going to have a further look underneath. re the damp proofing was going to use a few layers of liquid... so 'tanking' the whole base and up the inside of the brick courses and then the usual dpc under the sole plate.
 

That would work

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Ok yes see what you mean re damp ingress being almost impossible to stop long term through the bottom mortar if I were to go straight off the stone slabs. Im going to lay a concrete slab on top of the stones. Im thinking 75mm?
 

MikeG.

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Strong concrete, well cast, should be fine at 75mm if the base is absolutely rock solid. If in doubt, make it 100mm.
 

That would work

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Thank you. Due to the construction its going to be easier to use a liquid dpc (under a chipboard/osb floor) and up the inside of the brick courses which will in turn be covered with the internal osb lining.
And 5:1 all in ballast.
Does this sound ok?
 
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