Expert: Dave Johnson - 8/28/2009

Question
We recently had an outdoor living space designed and built.  Our architect called for rebar every three feet on the center and expansion joints where the patio slab meets the walls.  Unfortunately, the builder used fibermesh only and no rebar or wiremesh.  He also poured the patio (35x17feet) completely against the walls with no expansion joints.  The concrete was poured when the outside temp was over 90 degrees and control joints were cut approximately 7-10 days later.  Now our concrete is cracked!  Does the fibermesh offer any structural reinforcement like we would have had with rebar?  What is your knowledge on cutting stress joints this late and a slab this large with no expansion joints?

Answer
Hi Susie,
The mesh has little or no structural integrity. It may help keep the slab from separating where it cracks.  The joint cutting will be fine, but they have to be deep enough to create a weak spot to allow controlled cracking.

Were you aware that the contractor wasn't following the specs at the time? It sounds to me like you have some recourse if there was a specific contract....

On large slabs, the expansion joints are usually 30' apart, so your slab is not far off.

Mail me again if you need more...

Good luck
Dave