I want to add a floating concrete floor to a backyard barn type utility shed. It has a cement block foundation that the walls are on, but no floor. Do I use a form up against the wall, or put a piece of syrofoam in there or what to form the edge of the slab? Should I pull the form out after it sets? What do I use to fill in the crack between the floor and wall? It is 8' X 8'.

Be sure the sub-grade is compacted properly - nail asphalt impregnated expansion joint to the block being careful to level the top of the expansion joint and use this as the screed line. Once the concrete has cured you can seal the top of the expansion joint with a polyurethane sealer if you want but it's usually left open.

I got the site level and compacted and poured my concrete. Everything looks great. Thanks a lot. Also I made some cash on the deal, I took everything out of the shed to work on it and put it out on the lawn and everyone assumed I was having a yard sale, so I sold them some empty gas cans and a string trimmer and stuff. Ka ching!