As long as the thin top coat of concrete is cosmetic and not structural
you won't get in trouble but I recommend you put some steel in it if you
don't want to risk it breaking up later. Fence material is good sub for
rebar in a deal like this. The overlay will likely crack but the cracks
will be controlled if you use the fence material.
Another problem is that when the overlay concrete cracks some water will
eventually get in and when it freezes... Well you get the idea.
You might get better results if you drill a gazillion holes in your
current concrete and dowel the original slab to the new overlay with
rebar. I'd form the rebar with a right angle and sized so that the
rebar bottoms out in the vertical drilled holes and then runs horizontal
with at least 2 inches of concrete above and below it. The horizontal
part of the right angle pieces needs to have a minimum length of 25
times the diameter of the rebar. Using epoxy in the drilled holes to
secure the rebar would be better than depending on some concrete to end
up in the holes. I wouldn't think the rebar would need to be larger than
#4 and smaller should be fine. (In imperial measurement of rebar each #
is 1/8 inch so 3/8 inch nominal diameter is #3 and 1/2 inch is #4, etc.)
There are admixtures for adding to the mix before pouring to get better
adhesion and there are concrete glues intended to be "painted" onto the
substrate before pouring the top coat.
All of the above make for a better chance at survival but none
separately or in aggregate will absolutely guarantee the topping
doesn't crack, have water infiltrate it, and suffer freezing damage. The
above will improve your odds of survival.
Patrick NJ5G
On 2/4/2017 9:51 AM, Wes Stewart wrote:
The new concrete won't adhere very well to the old and will probably
crack.
(Here in AZ almost all houses are slab-on-grade. There is a saying,
"There are two types of concrete slabs, those that are cracked and
those that are going to crack.")
On 2/4/2017 8:26 AM, Paul Christensen wrote:
Thanks to all who replied by private e-mail. Many folks suggested
using a
concrete cutter to trim the base edges square. Yesterday, I went
back out
to the site and took some measurements of the leg bolts. There's ample
distance to overlay about 2 inches of concrete to the top surface and
extend
the base square from 10 ft. to 11 ft. with a new outer frame. I come up
with about 1 cu. yd of concrete. Four pieces of 2"x6"x12 ft. boards
should
do the trick. This is the concrete equivalent of capping a tooth. The
overlay is purely cosmetic and doesn't need to be part of the
original pour
which meets spec. Anyone see any issues with this?
Paul, W9AC
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