Replies

1. 
   DANL | May 07, 2005 09:56pm | #1

   You'll get good answers if you post this on the Fine Homebuilding "Breaktime" forum. Lots of guys there have said they like the concrete with the glass fibers.

1. 
   ValhallaPhil | May 10, 2005 01:21am | #4

   Thanks, I've moved it.

1. 
   DANL | May 10, 2005 03:49am | #7

   I saw it at the Breaktime forum. You've gotten good answers in both places though. Hope they help.

2. 
   WayneL5 | May 08, 2005 05:40am | #2

   Fiber additives do reduce shrinkage cracking, that is the purpose for them.  They don't, however, add any strength -- a common misconception.

   A stiffer mix will be less prone to cracking.

   The best thing is to make the cracks where you want them.  Typically that is done by sawcutting.  To be effective, sawcutting has to be done to 1/4 of the thickness of the slab.  Typically it is done the day after the slab was poured, with a diamond saw.  Concrete cuts fairly easily on that next day and has not yet shrunk much.  For your application, making sawcuts so they fall under the interior walls would put the cracks where they will do no harm.  I assume you will be installing tubing room by room.  With your sawcuts under the walls, they'll be in places where there will be no tubing.

   Careful planning and measuring is essential.

1. 
   ValhallaPhil | May 10, 2005 01:23am | #5

   Thanks!  I'm a stickler for detail so I should be able to do it.

3. 
   donpapenburg | May 08, 2005 08:39am | #3

   Compact your gravel bed

   use a dry mix, 4" slump.  if your concrete runs from one side too the other your concrete will be junk.  Water evaperating causes it to shrink(crack).

   Use 25psi exp foam under with a poly vb . Then cover after finnishing to slow evaperation.

1. 
   ValhallaPhil | May 10, 2005 01:29am | #6

   Excellent suggestions!  This is a great forum.

   Thanks,

   Phil