Replies

1. 
   IanDG | Jun 16, 2005 06:41pm | #1

   The purpose of the expansion cuts is crack control and they should be positioned so that any movement takes place within the expansion joint --- if you like, they are pre-determined cracks.

   There should not be any cracking anywhere else in the slab and if there is it's a sign that the expansion cuts were in the wrong place.

   IanDG

1. 
   brownbagg | Jun 16, 2005 08:19pm | #2

   yes the cracks are normal, concrete will almost alway crack on a corner or sharp point. they are thing you can do to reduce cracks, but it is normal. they is nothing you can do after the crack but tear out and replace.

1. 
   IanDG | Jun 16, 2005 09:31pm | #3

   "concrete will almost alway crack on a corner or sharp point."

   Then that's where the crack control joint should be put. Properly laid concrete, on a properly consolidated sub-base, with properly placed crack-control joints, should never crack.

   You're trying to justify bad workmanship.

   IanDG

1. 
   VaTom | Jun 16, 2005 10:01pm | #4

   Well, in my case it was ignorance.  Where were you?

   The rest of my control joints worked.  <G>  This slab is roughly 15'x70', going around the corner of the house.

   Quinhead, this joint hasn't moved in the last 9 yrs.  Opened up in the first year.  A further aggravating factor here is the 2" of XPS immediately under the concrete, plus my routinely driving a 5000 lb tractor over it.  Doesn't bother us, but this slab was done with friends, none of whom knew more than I did.

   The choices are live with it or replace it with the control joint properly placed.  Then you get a straight crack.  PAHS Designer/Builder- Bury it!

1. 
   IanDG | Jun 16, 2005 11:23pm | #5

   In the case you show, I'd have put a crack control joint from corner to corner if the walkway was 4' wide or less. With a wide walkway, the better solution is 2 control joints, perpendicular to the front and side walls and meeting at the corner so the part of the slab at greatest risk is completely isolated.

   A fibre-board or similar isolation joint between concrete and building would have been a good idea, too.

   IanDG

2. 
   VaTom | Jun 17, 2005 02:06am | #6

   Thanks for the critique.

   Hard to see, but there were 2 attempted control joints, meeting at the corner, leaving a pie-shaped center section.  Possibly I should have cut deeper, but the others worked.  Not sawn, scored.

   There is isolation from the building in the form of 2" XPS.  This is all part of my PAHS insulation umbrella, necessary for our cooling/heating system to work.  The copper sheathing extends about 3/4" beyond the 2" XPS separating the slab from the wall.  Drainage works well.  When I asked the plan approver for a definition of "grade", he knew something was odd.  Didn't want to know why I was placing XPS under an exterior slab, but agreed that footing depth wasn't going to be an issue.  Saved me a few yards of concrete.

   I had no idea how it was going to work with the XPS directly under the concrete, over washed stone.  Other than that one crack, extremely well. 

   Apparently I planned better than I'd thought.  Was only my second slab.  Not anything I'd do for a client, but the puddles aren't deep.  PAHS Designer/Builder- Bury it!

3. 
   Quinhead | Jun 17, 2005 02:56pm | #7

   Thanks for your input. We are very happy with the Driveway, walkway and concrete steps...really sets the house apart from the others with PT front steps and asphalt drives and walks.

   ....Quinhead

    

2. 
   Quinhead | Jun 17, 2005 03:07pm | #8

   Thanks for your reply. Me thinks that my wife wants to build again.... yikes, as this house is not exactly perfect. Anyway, will use your advice for the next driveway/walkway..... Quinhead