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Re: SLAB - Control Joints in Concrete Slab on Grade

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I noted in the question regarding control joints in slabs  that the
specification included Fibermesh which I am assuming is in lieu of steel
reinforcing. I also assume the reason control joints are of interest is to
control cracks.
I am involved in a project where slab floor cracks have become an issue. The
approved plans for this tract development specified welded wire mesh in the
4-inch floor/foundation slabs. The soils are not considered expansive. 
The models were constructed with the welded wire fabric, but when the rest of
the homes were built, the wwf was replaced with Fibermesh. That was 9-years
ago. Today, the tile flooring is cracked and loose, the vinyl flooring has
bumps and stains where there are cracks in the slab, and there are measured
slabs cracks up to 3/16-inch wide under the carpeting, in all of the houses of
this tract ...........except the models! 
The slabs of the models with the wwf have cracks, but all are hairline, with
no separations and no vertical displacement. 
All concrete slabs crack, and reinforcement cannot prevent that. But steel can
spread the cracks so that you have many hairline cracks, instead of a few wide
cracks. The steel reinforcing also keeps the cracks tight and provides
doweling between the pieces, something hair-thin Fibermesh cannot do. I
personally do not specify wwf because it often ends up at the bottom of the
slab due to poor installation, so I prefer #3 @ 18" for typical 4-inch slabs.
Fibermesh claims to minimize plastic shrinkage cracks, cracks that form during
the first few hours after placement, but the serious deep shrinkage cracks
cannot be prevented by reinforcing, only managed, and for that you need steel
and properly placed joints. 

Charles Laines, S.E.
Long Beach, California