Levelling/Tamping large concrete slab

[ahhwoodrow]

We're planning the pour of a concrete slab to form the base of our extension, the width is 8.5m and the projection is 5m. On three sides we have the concrete blocks built up to the finished slab level to allow us to use them as a guide, but on the fourth (8.5m) side is the current house.
How are we best to make sure the concrete finishes up level and well tamped down over this span? I haven't seen any 5m long boards etc that can span the whole distance.

 

[gregers]

can you not make up your own say with 3 boards.add a couple of handles so you dont have to bend down.

 

[pinenot]

If you fix say 2" x 1" timber around the perimeter walls where the concrete is to go,and trowel a platform about a foot wide out/in from the walls i.e. into the slab footprint this provides a reference by which to lay the concrete level. just start at the furthest point and work back in stages, Oh! and leave the timbers high by a couple of mills to allow you to trowel under but up to the timbers. Remove timbers after conc sets...pinenot