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RE: Control Joints in a Mat Foundation

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I use ¼ T myself, but in this case you will have top and bottom reinforcing. I would say that your weakened plane joints should maintain the clear cover requirements and space them on a grid where you have a distance no greater than 12feet in either direction. Probably nothing deeper than 1”.


No technical data to support this, the joints are there to minimize shrinkage cracking at the surface. I’m sure someone like Harold will give the 100% correct answer.





-----Original Message-----
From: Bill Allen [mailto:T.W.Allen(--nospam--at)]
Sent: Thursday, October 27, 2005 12:28 PM
To: seaint(--nospam--at)
Subject: Control Joints in a Mat Foundation


I am working on a project which consists of a single story wood framed building sitting on a mat foundation. The mat is 16” thick.


A field question has come up regarding control joints. In a typical slab-on-grade, I specify cuts one third the slab thickness spaced no more that 3T feet where “T” is the slab thickness in inches. These recommendations don’t make a lot of sense for a 16” “slab”.


What would be a more appropriate guideline for this situation?




T. William (Bill) Allen, S.E.


Consulting Structural Engineers