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RE: Concrete slab on grade - natural cracking

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How is the natural crack different from a saw cut?  The saw cut is partial depth, but it is part of a crack that occurs due to shrinkage. All of the slab below the saw cut has natural aggregate interlock as well.  Why wouldn’t a natural crack have a tendency to curl as well?  Perhaps it wouldn’t be as noticeable since the joints are not perpendicular, but I would assume you would still get some curling.


If you leave it up to God to put in your crack joints you may not like where He puts them.





-----Original Message-----
From: Ken Peoples [mailto:kspeoples(--nospam--at)]
Sent: Thursday, June 02, 2005 3:54 PM
To: Seaint
Subject: Concrete slab on grade - natural cracking


We have a project with a wood gymnasium floor on sleepers.  We have specified control joints in the slab (both sawcut and formed keyed joints).  The contractor is telling us that he would prefer to not put the sawcut control joints in and just leave the slab crack wherever it needs to crack.  His reasoning (besides saving the cost of sawcutting) is that he has had bad experiences with curling at the sawcuts that have needed to be ground down.  Apparently when the slab just cracks wherever it wants to, the aggregate keeps it from curling.  I have not heard this argument before, but I can see the logic in it.  I know that this would be a problem where reflective cracking might be a concern (such as a tile floor), but since there are wood sleepers and then a wood floor above that, I wonder if he is correct.  This may be a case where less work is better.  He claims that many large slabs (like K-Mart or Wal-Mart type buildings) are being done this way today.


I look forward to reading the collective wisdom on this topic.


Best regards,




Kenneth S. Peoples, P. E.
Lehigh Valley Technical Associates, Inc.
1584 Weaversville Road
Northampton, PA 18067


Phone: 610-262-6345
Email: kpeoples(--nospam--at)