surface bonding

[Julie Rehmeyer <julie@math.mit.edu>]

While we're on the subject of surface bonding...

We used surface-bonded concrete for a bridge we built last winter.
For our purposes then, we were extremely pleased with it.  We
core-filled the blocks -- surface bonding would certainly not have
been sufficient for the loads on our (vehicle-bearing) bridge -- and
so for us the surface bonding served the roles of stablizing the
dry-stacked blocks for the fill, waterproofing (we didn't have to use
bitumen, a real blessing), and, since we used a colored surface
bonding mix, for appearance.  Dry-stacking really saved us a lot of
time, particularly when we realized that we didn't have to be really
careful about levelling the blocks with sand -- we found that the
the blocks needed to be fairly significantly off-level for it to
matter.  And it made a huge difference in terms of appearance; we
essnetially got a plaster job out of it for almost nothing.  One quick
comment on that, though, is that we ended up having to put a second
coat of the surface-bonding cement on for color because it was
impossible to keep the first coat in reasonable condition throughout
the whole construction process.

One incovenience of the method for some applications is that concrete
blocks are sized to work with mortar, i.e., an 8x8x16 block is
actually (I think) 7 5/8 x 7 5/8 x 15 5/8, so the dimensions end up a
little odd.  That didn't really matter for us.

I personally would do surface-bonding in most situations where I was
inclined to use blocks.

Julie