Slab on top of a stem wall

[jdwill100]

I will be pouring a 4 inch slab on top (not in between) of a concrete stem wall for which a 16' X 20' shed will be built on. My question is to whether or not I should cut expansion joints in the slab? I will be using 6" remesh in the slab with the remesh being connected to the stem wall. My first thought was to cut expansion joints, but then I wondered how the movement would affect the studded walls above the slab. The stem wall is 6" by 2' and has 3/8" rebar in it. Thanks for any thoughts/advise on this.

Jack

[Richard A Hetzel]

It's a mistake to pour the slab on top of the stem wall, unless the slab is very carefully engineered, with a thickened edge (like a transition to 8-inch thickness over about 4 feet), and engineered reinforcing design, not just mesh. If you pour a 4-inch slab on top of the stem wall, it almost guarantees cracking all the way around. There is no need for expansion joints in a slab of that size, but there is a need to accomodate relative movement between the slab and the stem walls, which won't be possible with the slab poured over the walls.