[AT] another new shop

[Spencer Yost]

While I did work for an engineering company testing concrete and soil in
the early 80s before I finished school, I don't consider myself an expert
so I did not answer this thread.   However, I did see a few things (and a
few I didn't) I wanted to comment on:

1 - Slabs are only as good as your base.  Drainage had better be great.  If
your stone sinks or 
settles, then you will have cracks.

2 - Fiberglass prevents cracking - it will not hold it together once it
does as someone
suggested.  Floor is fuzzy afterwards too!

3 - Mesh doesn't prevent cracks, it holds together after the crack, but
then only until it rusts 
through in a few years.  Rebar will help prevent somewhat , but it is
really overkill and slabs are not 
rebar's forte anyways.  It's forte is really to prevent total shear failure
and collapse in columns 
and joints and angles(if you have tested concrete, you know how that looks
and sounds!)

4 - Install mesh and rebar well if you use them.  Poorly installed they
cause more 
problems than they prevent

5 - High PSI concrete isn't necessary:  In fact it can be too brittle after
a few years.   The 3500 
as suggested is fine though you could go to 5000.   The higher PSI's main 
advantage in a slab is the high PSI concrete seems to be, at most yards,
more carefully mixed 
and the quality is more closely controlled.

6 The 1" slump as suggested is too stiff - 1.5-3" in a cone mold is fine.
Less than 1.5" and you can 
not be sure there has been complete saturation.

7 - Joints every so often.  Exact distance isn't a big deal, just split
your shop 
up into 2 or 3 even sections in each direction

8 - If the finishers want it looser, make them use plasticizer instead of
water.

9- SUPERVISE SUPERVISE SUPERVISE   Finishers will water it like there is no

tomorrow if you don't

Good luck, and remember, concrete can only be guaranteed against fire and
theft, not cracks.  (-;  Tractors drive over little cracks anyways.

Spencer
40x30 shop with a 6 year old 4" slab on a THICK
1.5' to 3' bed of gravel with fiberglass, 2 floor drains, 
no rebar, no mesh, and a french drain at the uphill side
No cracks(yet).