[TowerTalk] Tower Foundation Pouring

[Patrick Greenlee]

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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