Replies

1. 
   Piffin | Jan 08, 2004 06:02am | #1

   If not settleing foundatiopn, my first guess is that there was a high portland content in the mortar. That makes for a much harder and more brittle job. The older mortars were higher in lime which is somewhat flexable, and self healing.

   The individual brick - any brick can crack. It may have been an underlying invisible fracture when laid but the stress of loading, shrinking, and fires could expose it.

   I'm sure there are more things too.

   .

   Excellence is its own reward!

1. 
   cutawooda | Jan 08, 2004 06:20am | #2

   I am no genius....boy! thats for sure...explain to me the theory,..no,.not theory, the chronilogical order of things as they occur during settling. What I am getting at is this:

   What causes those famous cracks you see in homes that zig zag diagonally through the bricks. Is it movement from twisting, sheering, or has the slab cracked close to that point. And if the latter is the case, would you not be able to see the crack around the perimeter somewhere.  I dont mean to get particular and waste your time..but I am truly curious about my bricks cracking.  I am, as you would expect, upset to see my bricks cracking. I know that this clay soil and dry weather are the culpret, but I am still trying to analyze this situation. I appreciate your response, as well as your other responses on different issues.

1. 
   Piffin | Jan 08, 2004 07:15am | #3

   Zig Zag or stair step?

   Probably stair step following the mortar joints. This would be from foundation movement or settling. You might not see a crack in the slab/footing. Developing a very slight crown from settling can parlay into a pattern like that..

   Excellence is its own reward!

1. 
   cutawooda | Jan 08, 2004 07:28am | #4

   so, concrete bends?

1. 
   SamT | Jan 08, 2004 07:34am | #5

   cuta,

   everything bends,  some, not so you would notice,  some, like rubber.

   SamT

   "You will do me the justice to remember that I have always strenuously supported the right of every man to his opinion, however different that opinion may be to mine. He who denies to another this right, makes a slave of himself to his present opinion, because he precludes himself the right of changing it."   Thomas Paine

2. 
   Piffin | Jan 08, 2004 08:04am | #6

   Darn right it bends.

   When you first mix it, it bends really good. It'll even bend enough to run through a pumper hose or let you use tools to push it around.

   That is when it is in the plastic state.

   But it doesn't cure in an instant, Bif Powie done!

   It is a long slow process. Not uncommon at all to pour and then build over it while still only seventy percent of design strength. So you are adding weight to it as it cures slowly. If you built over clay sol and it is drying/shrinking at the same time, the soil under is moving - possibly unevenly - while the weight is being added above. So it bends. Sometimes it doesn't bend so much, and it cracks instead.

   Concrete is an amazing product. Did you know there have been concrete canoes built that do better than ABS ones?.

   Excellence is its own reward!

3. 
   caseyr | Jan 09, 2004 03:13am | #9

   Article on concrete racing canoes:

   http://www.schundler.com/canoe.htm

   My office at UC was next to the building where they constructed these things:

   http://www.ce.berkeley.edu/~canoe/

4. 
   IanDG | Jan 08, 2004 06:10pm | #7

   The cracks are almost certainly caused by settlement but you ought to check if the structure is still moving. The best way is to use a small strip of glass across the crack, fixed with epoxy glue, so that any further movement breaks the glass.Concrete does flex but if the sub-base was consolidated properly the slab shouldn't deflect.Was the fireplace brickwork tied back into the exterior wall?

   IanDG

5. 
   cutawooda | Jan 09, 2004 02:12am | #8

   no. and the hearth is merely bricks laid on the slab