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Cliff Rohrabacher
04-20-2007, 12:22 PM
Slab construction with Blocks, bricks, or stone and mortar.


Won't the slab break the walls apart ( or shear the bond to the slab) when the slab expands and contracts~??

Bob Childress
04-20-2007, 4:18 PM
Home builders do it all the time. I don't think they would (or could) if there were always problems. The more pressing concern, IMHO, would be the slab heaving or sinking during settlement. :)

David G Baker
04-20-2007, 7:35 PM
Cliff,
Expansion joints and an expansion pad between the slab and the walls. It has been a while since I have been around the material so I don't recall the correct name of the stuff. It is approximately 1/2 to 3/4 inches thick and varies in width from 3 inches up. The material is compressible and adsorbs most of the pressure that concrete creates from expansion and contraction.

Rich Stewart
04-21-2007, 1:33 AM
Down south they call it 'bear hide'.

Cliff Rohrabacher
04-21-2007, 10:49 AM
Expansion joints I have seen 'em on large slab work made from fibrous material as well a rubber-like material.


and an expansion pad between the slab and the walls.

Are you saying that the masonry block walls are not bonded to the slab?? Is a strip of expansion material placed on the slab before the first blocks go on and then the blocks are then laid on top of a strip of expansion material?

So then. . . Ummm . . . A 6" - 12" high knee wall as part of the slab pour would be the best way to prevent any ambient temporary surface water or moisture from entering the structure??

Per Swenson
04-22-2007, 9:47 AM
I am missing something.

Like a footing.

Yes even for a slab.

Out side perimeter footing 8 inch thick concrete by 16 inch with rebar at the

frost line. 12 inch concrete block filled solid in corners and any

load bearing wall intersections, to 4 inch's below final slab height.

Right angle rerod in block bent to 90 degrees to tie the slab to the

walls. Pour it. Concrete cut expansion joint.

If I am missing something I apologize.

Per

David G Baker
04-22-2007, 8:30 PM
Cliff,
I misunderstood you. I thought you were talking about where a horizontal slab meets a vertical wall. I should have spent more time looking at your post.

Curt Fuller
04-22-2007, 10:22 PM
Slab construction with Blocks, bricks, or stone and mortar.


Won't the slab break the walls apart ( or shear the bond to the slab) when the slab expands and contracts~??

Concrete varies somewhat from one region to another because of differences in the aggregates. But concrete is at it's greatest volume at the time it's being placed. From that point it shrinks as any water in excess of that needed for the hydration of the cement evaporates. Most cracks in concrete are the result of that shrinking and it's refered to as plastic shrinkage. So the term 'expansion joint' is sort of a misnomer. It's actually a 'slip joint' that allows one slab to move independent of another it's adjacent to and that helps to prevent the heaving or settling of one slab from breaking the other. If you look closely at the joint where a slab and a wall meet there is always a small void regardless of whether expansion joint was used or not. The two most important factors in placing concrete to avoid cracks, heaves, settling and other such problems are the type of material that it's placed on and good compaction of that material. Heavy soils, clay and such hold mositure so that when it freezes and expands it causes heaving. They're also harder to get good compaction resulting in settling. Granular materials such as crushed rock, road base, or even coarse sand allow for the moisture to drain and they compact much tighter.

Sorry that was a little long winded but I hope it helps.