Depth of concrete required for a workshop floor

by Daniel Phipps
(Wiltshire, UK)

Q. I am having a new workshop built.

The dimensions are 30' x 25', l am having the foundation base dug to 8"

One side of the workshop will be for wood machinery, the other, lathe milling machines etc. The heaviest being the milling machine at around 1400lbs

Down the center, l will need to cut a groove of 12" x 2" deep to accommodate the railway track.

Q's:

Is 8" of concrete too much or will 6" do?
Do l need a reinforcement in the concrete?
How far apart should the expansion joints be?

I really need some good advice!

A. Six inches of 4000 psi concrete will be enough as long as you have a good 18" compacted gravel sub-base. I would tie a mat of 1/2" rebar 18" on center each way for reinforcement and use fibermesh in the concrete as well. That may be a little over-kill but for the money, well worth it.

The expansion or contraction joints should be cut as close to 10' x 8' squares as you can get them.

Make sure the concrete isn't poured too "wet" or loose. A 5 to 6 inch slump would be easy enough to work with without compromising strength. After the concrete is troweled and sawed, you should apply a concrete curing & sealing compound to cure the concrete.