How to Finish Lightweight Concrete

Screed the surface immediately after pouring the lightweight concrete. Pull a straight 2-by-4-inch board across the form boards around the concrete, pulling excess material from high spots and filling in low spots.

Sweep a darby -- a long trowel with two handles -- across the surface of the concrete in wide arcs. Fashion a darby by securing a handle onto a straight 1-by-4-inch board. Use the darby to fill in holes and marks left by the screed.

Allow puddling water to be reabsorbed before continuing. This puddling of water on lightweight concrete is a temporary, normal process. Allowing the water to be reabsorbed encourages a stronger surface.

Run an electric edger around the edges of the concrete firmly pressing your gloved finger into the surface leaves only a 1/4-inch indentation. Hold the electric edger firmly against the concrete's surface as you guide it, but do not gouge it into the surface.

Make contraction joints in the lightweight concrete as required by your specific project with a concrete saw. Driveways and garages typically require contraction joints, or grooves, at 10-foot intervals. Smaller slabs call for 4-foot intervals. Ensure the groove is a quarter of the thickness of the concrete.

Float the surface of the concrete to produce a rough texture with a rubber float. Swinging the float from side to side will remove most of the marks left by the screed and darby.

Smooth the lightweight concrete surface with a steel trowel, using the same swinging motion. For a nice, slightly textured finish, sweep the troweled surface with a stiff household broom.