WaterPROOF expanding foam needed

[MPEJ]

i have built a metal shed to be used as a workshop with a foundation of edge mounted 8x2 joists for it to sit on.
It is sat on a concrete patio that has proved to be uneven with rain water run off ingress under the joists through a number of gaps where the ground dips away.
I'm looking for a waterproof expanding foam that will block this water ingress (which currently leaves a puddle in the middle of my workshop).
Are there any suggestions? I can't seem to find anything that is labelled waterPROOF only waterRESISTANT or weatherproof and I need something that won't absorb water and start to rot the timbers/introduce damp.

 

[MPEJ]

 

[JohnD]

if your wooden bearers are on the paving, they will get damp and rot. I don't believe foam or sealant will do the trick. I'd suggest one or two courses of brick instead. You can lose the unevenness with your mortar bed. And put the shed on top, bolted down to the concrete.

 

[freddiemercurystwin]

Aye, one course of brick, layer of dpm, timber bearers.

 

[MPEJ]

No permanent structure fixings permitted I'm afraid as the watercourse for the street runs underneath.
I forgot to add that bit, apologies.

I've coated the external faces and edges of the wood with tar paint but I'm not looking for it to last forever as I'll be selling the house at some point in the next couple of years once I've finished renovating it.

The workshop serves as a place for non structural renovations to occur.

 

[freddiemercurystwin]

A single course of brick is hardly structural and in fact I would argue you wouldn't even need to cement them down.

 

[JohnD]

but I think mortar would block water running in, as well as levelling the surface.

 

[Doggit]

You should have started with concrete block laid flat first, then you could have used tanalised 4x3 instead of 8x2s, and leveled the base before putting the shed on. The water would have run between the blocks, and the timber would have been out of the water, and tar paint would have meant it'd have lasted forever. These sheds are designed to have either a metal frame on the floor that you concrete over, or a wooden floor, but you've made no provision for the floor, so have created a problem that didn't need to exist I'm afraid.