Cob RE: Robert Bolman's comments on 'used' concrete foundation

[Robert Bolman]

>Good info!  Did you have to put any kind of reinforcing between slab
>layers?
No
>Did you tie it together vertically other than with the cement
>mortar?
No
> Was your top bond-beam the full two foot width of the top of
>foundation?
Yes
>How much steel and what size in bond-beam?
Four pieces of half inch rebar toward the bottom of the bond beam.
>Was this solution
>engineered or a seat-of-the-pants requirement from the bldg. dept.?
I explained what I wanted and my engineer made it fly.
>I wonder if it would be less labor-intensive to start with your 3' wide
>base pieces, then dry-stack the narrower slabs up from there, maintaining
>a relatively vertical inside face outset about 8" from the inside line of
>your base pieces and farther offsetting the top two rows about 4" more;
>(have I lost everyone yet?)
Well, actually you did.  It's late.  I'll try reading it again
tomorrow.  -Rob
then run some 6" x 6" 10-10 welded steel wire
>mesh (or equivalent)) up the inside face of the resessed stack from the
>top of the base pieces to the top of the foundation, then form an inner
>surface ~ 4" in from the inner face of the dry-stack from base pieces to
>top (using salvaged plywood, pinned strawbales, cob or whatever), put a
>couple of # 4 or 5 bars in that top widened space where the dry-stack is
>inset an extra 4" and pour it all with a fairly wet concrete mix and
>vibrate it well (manual or mechanical).
>
>What you'd end up with would be a monolithic unit with a 3' base, ~ 4"  of
>concrete bonded to and filling the gaps in the dry-stack all the way up
>the inside, the poured concrete widening out to 8" for the top 8" to 10"
>(two slab thicknesses) to form a bond-beam, and most of the mass and the
>entire exterior face consisting of recycled concrete.
>
>This would greatly reduce the amount of new poured concrete over what
>would be used in a conventional footing and 8" foundation wall, save the
>labor (and time) of mortaring all the slab chunks together, assure better
>lateral strength than a vertically un-reinforced mortared foundation wall,
>probably use no more cement than the mortared approach with full width
>bondbeam, give an exterior surface of broken concrete which could be
>ferro-stained to give a nice, warm tan color and rugged texture to blend
>with earthtone stucco above, provide less tendency to wick up moisture
>from below, keep a lot of "waste" concrete rubble out of the landfill and,
>hopefully, still please the building department.