[Salmo]

I have a good 6ft X 4ft shed sat upon 4 courses of brick. The floor is slabs set on earth and gets very damp. What is the best way to waterproof the floor. My thoughts are a sheet of membrane with 2in of concrete on it.

[Kristen]

Don't know anything about it, but do you need the concrete?  Would membrane + earth (sand might be easier to lay slabs on?) + Slabs do instead?

[bravemurphy]

Membrane would be the best but put a blinding of sand under it to stop any sharp bits penetrating the membrane.

[ambodach]

I have a good 6ft X 4ft shed sat upon 4 courses of brick. The floor is slabs set on earth and gets very damp. What is the best way to waterproof the floor. My thoughts are a sheet of membrane with 2in of concrete on it.

Salmo - do you mean by "4 courses of brick" that the shed is 12" off the ground - or is this 4 support points of one brick - ie 3" off the ground.  It does make quite a difference to what you are trying to achieve.

One thing you do have to think on is quite where this damp floor is with respect to the bottom faces of the shed walls  -there is little point in trying to keep the 'support' points dry if the rest of the shed is getting damp from the current floor.  Another query - do the 'brick' supports have a damp proof membrane, as again moisture will pass through the bricks.

Without removing the shed and sorting the base area such that it is sealed from damp in the manners suggested above, I don't think you are going to solve the problem; trying to retrofit a membrane and getting it moisture proof with the shed in position I don't think is realistic. 

I would dig out the current floor, making sure that all the shed wood has good ventilation and go for putting in suitable supports for waterproof plywood or OSB - see this typical website for guidance

http://www.tbrewer.co.uk/sheet-materials/guide-to-constructional-plywood-a-osb