Repair a concrete slab opening
 

Hi I used a jack hammer to open the 4" concrete slab and made a trench for
the plumber to come to redo the underground pipe fittings.

Once they are done I need to pour the concrete slab back.

Question I have is...

(1) As I broke off the old concrete slab, there were a lot of the large
chunks of concrete I have as debris. Should I use those to fill in the
trench up to the 4" mark below grade, or should I use sand and pack them
tight?

(2) There were wire mesh inside the concrete slab that I broke up. The
trench is about 8" to 12" wide about 10 feet long. Is there anything I need
to do as far as the wire mesh? Should I cut another wire mesh of that size
and put it in? The way many of them broke off I am not sure I can tie back
to the old ones.

(3) Underneath the concrete slab is a sheet of plastic, is that a moisture
barrier or some insect barrier? Now that it's broken what can I do to have
the same effect?

Thanks,

MC

Repair a concrete slab opening
 

MiamiCuse wrote:
Hi I used a jack hammer to open the 4" concrete slab and made a trench for
the plumber to come to redo the underground pipe fittings.

Once they are done I need to pour the concrete slab back.

Question I have is...

(1) As I broke off the old concrete slab, there were a lot of the large
chunks of concrete I have as debris. Should I use those to fill in the
trench up to the 4" mark below grade, or should I use sand and pack them
tight?

I would definitely not use the pieces of concrete. They may settle in
odd ways.

(2) There were wire mesh inside the concrete slab that I broke up. The
trench is about 8" to 12" wide about 10 feet long. Is there anything I need
to do as far as the wire mesh? Should I cut another wire mesh of that size
and put it in? The way many of them broke off I am not sure I can tie back
to the old ones.

The mesh is there for crack control. I doubt that you would need to
worry about a crack spreading from new floor to old floor. But
someone with more knowledge may know better than I do.

(3) Underneath the concrete slab is a sheet of plastic, is that a moisture
barrier or some insect barrier? Now that it's broken what can I do to have
the same effect?

Moisture barrier. I would cut a piece of plastic (could be 4 mil) and
place it in your trench. You could try to glue it to the old moisture
barrier. I have not seen people do this, but I cannot imagine it
would hurt in any case. Use a glue rated for below grade (obviously).

mh

Repair a concrete slab opening
 

A rule of thumb is to use aggregate no bigger than 1/3 the slab
thickness.

Repair a concrete slab opening
 

On Oct 10, 9:32 pm, "MiamiCuse" wrote:
Hi I used a jack hammer to open the 4" concrete slab and made a trench for
the plumber to come to redo the underground pipe fittings.

Once they are done I need to pour the concrete slab back.

Question I have is...

(1) As I broke off the old concrete slab, there were a lot of the large
chunks of concrete I have as debris. Should I use those to fill in the
trench up to the 4" mark below grade, or should I use sand and pack them
tight?

As long as they're not pressing on the pipe, sure use them as fill.
Just make sure that whatever you put down is well compacted. Lift and
drop a sledgehammer over the entire trench fill then smooth out the
surface.

(2) There were wire mesh inside the concrete slab that I broke up. The
trench is about 8" to 12" wide about 10 feet long. Is there anything I need
to do as far as the wire mesh? Should I cut another wire mesh of that size
and put it in? The way many of them broke off I am not sure I can tie back
to the old ones.

It really doesn't do all of that much. If your slab wasn't cracked to
the point that the sides were uneven, it's not going to prevent
anything. The subgrade preparation was adequate and the mesh was used
as insurance. If it makes you feel better, put it in - it can't
hurt. Just won't help if you prepare the trench subgrade properly and
place the concrete correctly.

(3) Underneath the concrete slab is a sheet of plastic, is that a moisture
barrier or some insect barrier? Now that it's broken what can I do to have
the same effect?

Put some more plastic back. Again, it's not going to do much as
there's no real way of sealing poly to poly easily. It's cheap and
easy enough to do, but any little gap will allow moisture to migrate.

R

Repair a concrete slab opening
 

"MiamiCuse" wrote in message
...
Hi I used a jack hammer to open the 4" concrete slab and made a trench for
the plumber to come to redo the underground pipe fittings.

Once they are done I need to pour the concrete slab back.

Question I have is...

(1) As I broke off the old concrete slab, there were a lot of the large
chunks of concrete I have as debris. Should I use those to fill in the
trench up to the 4" mark below grade, or should I use sand and pack them
tight?


I've done that couple of years ago using chunks of concrete from another
project - no problems so far. As mention elsewhere, make sure its compacted.
I would have used a concrete vibrator for extra insurance if I had one than.



(2) There were wire mesh inside the concrete slab that I broke up. The
trench is about 8" to 12" wide about 10 feet long. Is there anything I
need to do as far as the wire mesh? Should I cut another wire mesh of
that size and put it in? The way many of them broke off I am not sure I
can tie back to the old ones.


I would drill holes on both sides of the existing slabs for the rebar to pin
the new pour in place to keep it even over time.

(3) Underneath the concrete slab is a sheet of plastic, is that a moisture
barrier or some insect barrier? Now that it's broken what can I do to
have the same effect?


I would just add a new sheet of plastic like other mention - not much more
you could do. Its for moisture barrier more than anything else. I found out
for exterior installations if you don't use it, tree suckers will find the
smallest cracks to pop out even if its 20' or more under the slab.



Thanks,

MC

Repair a concrete slab opening
 

"RicodJour" wrote in message
ups.com...
On Oct 10, 9:32 pm, "MiamiCuse" wrote:
Hi I used a jack hammer to open the 4" concrete slab and made a trench
for
the plumber to come to redo the underground pipe fittings.

Once they are done I need to pour the concrete slab back.

Question I have is...

(1) As I broke off the old concrete slab, there were a lot of the large
chunks of concrete I have as debris. Should I use those to fill in the
trench up to the 4" mark below grade, or should I use sand and pack them
tight?

As long as they're not pressing on the pipe, sure use them as fill.
Just make sure that whatever you put down is well compacted. Lift and
drop a sledgehammer over the entire trench fill then smooth out the
surface.

(2) There were wire mesh inside the concrete slab that I broke up. The
trench is about 8" to 12" wide about 10 feet long. Is there anything I
need
to do as far as the wire mesh? Should I cut another wire mesh of that
size
and put it in? The way many of them broke off I am not sure I can tie
back
to the old ones.

It really doesn't do all of that much. If your slab wasn't cracked to
the point that the sides were uneven, it's not going to prevent
anything. The subgrade preparation was adequate and the mesh was used
as insurance. If it makes you feel better, put it in - it can't
hurt. Just won't help if you prepare the trench subgrade properly and
place the concrete correctly.

(3) Underneath the concrete slab is a sheet of plastic, is that a
moisture
barrier or some insect barrier? Now that it's broken what can I do to
have
the same effect?

Put some more plastic back. Again, it's not going to do much as
there's no real way of sealing poly to poly easily. It's cheap and
easy enough to do, but any little gap will allow moisture to migrate.

I cannot seal them anyways, as some of the plastic sheets are torn at the
edge where the concrete broke off so most of the edges do not have any
plastic protruding just along a few spots. So there is no way to have that
seal. Unless I loosen the sand under the concrete slab all the way around
the edges six inches in or so, then glue a thick 10" strip from the
underside onto the existing barrier, then fill in the sand to the bottom of
slab, then add in a new piece to glue to the other side of the strip, then
fill with concrete. Probably not worth it I guess.

MC



R

Repair a concrete slab opening
 

(1) As I broke off the old concrete slab, there were a lot of the large
chunks of concrete I have as debris. Should I use those to fill in the
trench up to the 4" mark below grade,

No..I'd ditch them, cover my new pipe/fittings with sand and refill the
trench with 3/4" to 1/2" *minus* aggregate with FINES and compact well
before repouring the 4" slab. Plain sand doesnt compact well. Moisten the
"old" concrete edge so the new stuff will adhere better.

(2) There were wire mesh inside the concrete slab that I broke up. The
trench is about 8" to 12" wide.... wire mesh?

Dont worry about a 8-12" wide cut


(3) Underneath the concrete slab is a sheet of plastic, is that a moisture
barrier .. Yes

Replace it with some 6 mil vapor barrier and tape the NEW to the OLD with
RED Tuck Tape making a good seal. It keeps any moisture below the
slab...Below the slab.