I intend to pour a slab where my deck steps will land. The dimensions are
approximately 80"x24"x6" (LxWxD) or roughly 6-2/3 cubic feet. The ready-mix
plants in town won't take an order for anything less then 2 cubic yards, so
I'm left to mix Quikcrete in my wheelbarrow. I'm thinking mixing 20 40#
bags of Quikrete is going to be a huge chore, so I'm wondering if I can
break up an existing concrete slab (the wife decided she wanted the steps
somewhere else) and use that as filler material -- not to save money but
rather to cut down on the amount of mixing I will have to do. Is this a
stupid thing to do? Would it considerably weaken the slab? If not, what
would your filler-to-mix ratio be? Thanks for any advice.
Why not just order the 2 yards of ready mix. They take back what you don't
use..your close to 1 yard as it is, it's simply a minimum order, they do not
require you to accept the full order, they never do. So what if you pay for
the extra yard, well worth it with the time you'll save plus all the back
breaking labor it would be to mix 20 bags!
Rent a mixer. This is only about 13-14 60 lb bags and that is trivial
with a mixer. Most will hold 2-3 bags a load.
I have a cheap mixer I bought many years ago and I will do 12 bags in
a single session with no help. 2 guys really makes it go faster. One
runs the mixer, the other places the concrete.
A lot of the home type mixers are advertised as
1/3 yard but I've seen some that are a lot
smaller, maybe 1-1/2 cubic feet. Ours was 1/3
but I think we usually mixed a bit less than
that per batch. I remember counting the shovels of
cement and gravel mix.
My dad did the whole foundation and basement
walls,and helped with the basement floor when I
got out of the service. A lot of work .
As far as the OP's question, yes filler is a
stupid idea. A small pad is no problem as it is
only 2-3 wheelbarrow loads. Just be sure to use a
very sturdy hoe for mixing.
I have seen "natives" break up concrete slabs just to use the pieces as
aggregate. No reason you can't do the same. If you combine the extra
aggregate with a bag mix, you might add some additional pure Portland cement
to the mix to keep the mix workable without reducing the strength. (The
strength is mostly a function of the water/cement ratio. If you add water
to keep the mix workable and don't add extra cement you end up with a weak
If you don't want to break up the pieces to "aggregate" size, you can get
some mortar mix and put them back together as a "rubble wall."
Us farmers have been doing this forever. I use rocks, bricks, broken
cement blocks and busted cement. It works just fine. There are a few
(the word "rocks" refers to any concrete or actual rocks)
1. Keep the tops of the rocks at least one inch below the surface.
2. Wet the underlying soil, place the rocks and walk across them to
push them into the soil.
3. Add a little extra portland cement to the mix so it adheres to the
rocks better and makes a strong mix
4. Wet the rocks just before you pour the cement.
I have never had one of these slabs crack.
PS. You might be cheaper buying portland cement, sand and stone,
rather than quikcrete.
IF you have to buy the sand and stone in BAGS, you are usually better off
just getting the quikcrete because the cost will be about the same and you
don't have to guess about the mix.
If you get the sand and stone in bulk, there is no question which is
I however always buy bulk. I did a 12X12 slab in a shed. The
portland (3 bags) cost me $22. The sand + stone cost $9. Of course I
have an old mixer and that helps. I also added all the rocks and
stuff as fill.
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