In preparation for a basement bathroom, I removed a 6' x 7' rectangle
of the concrete slab to run a bunch of drains over to the main stack.
My question is:

Before I re-pour this section with new concrete, should I dowel in
rebar around the perimeter of the existing concrete to keep the new
section from sinking? If so, what length of rebar and how far do I
dowel it in to the existing? Or are there easier methods that would
prevent sinkage?

wrote:

In preparation for a basement bathroom, I removed a 6' x 7' rectangle
of the concrete slab to run a bunch of drains over to the main stack.
My question is:

Before I re-pour this section with new concrete, should I dowel in
rebar around the perimeter of the existing concrete to keep the new
section from sinking? If so, what length of rebar and how far do I
dowel it in to the existing? Or are there easier methods that would
prevent sinkage?


Dowels are a good idea and I always use them in this type of
situation. Your dowels should be at least #4s at 16" on
center around the perimeter. Start at about 6" from the
corners. They should extend about 6-8" into existing concrete
in the very center of the slab vertically.

In addition and actually more important; Backfill and compact
the area under the new patch/slab. The soils in your area
will determine what is the best way to do that.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX

Thanks for the advice. What length of rebar do you suggest? Also, do
I simply drill holes into the existing slab and hammer in the dowels
(dry) or do I need to add some kind of epoxy to the holes?


Robert Allison wrote:
wrote:

In preparation for a basement bathroom, I removed a 6' x 7' rectangle
of the concrete slab to run a bunch of drains over to the main stack.
My question is:

Before I re-pour this section with new concrete, should I dowel in
rebar around the perimeter of the existing concrete to keep the new
section from sinking? If so, what length of rebar and how far do I
dowel it in to the existing? Or are there easier methods that would
prevent sinkage?


Dowels are a good idea and I always use them in this type of
situation. Your dowels should be at least #4s at 16" on
center around the perimeter. Start at about 6" from the
corners. They should extend about 6-8" into existing concrete
in the very center of the slab vertically.

In addition and actually more important; Backfill and compact
the area under the new patch/slab. The soils in your area
will determine what is the best way to do that.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX

wrote:

Thanks for the advice. What length of rebar do you suggest? Also, do
I simply drill holes into the existing slab and hammer in the dowels
(dry) or do I need to add some kind of epoxy to the holes?


Please don't top post!

I usually use 16" long dowels and tap them into place. In
some instances (usually where the new slab is abutting an old
slab and therefore subject to movement away from the old) I
will epoxy the dowels in place. That is usually unnecessary
when the new is encompassed completely in the old slab.
Lateral movement is not possible in that situation. Unless
you drill oversize holes for the dowels, you will be fine.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX


Robert Allison wrote:

wrote:


In preparation for a basement bathroom, I removed a 6' x 7' rectangle
of the concrete slab to run a bunch of drains over to the main stack.
My question is:

Before I re-pour this section with new concrete, should I dowel in
rebar around the perimeter of the existing concrete to keep the new
section from sinking? If so, what length of rebar and how far do I
dowel it in to the existing? Or are there easier methods that would
prevent sinkage?


Dowels are a good idea and I always use them in this type of
situation. Your dowels should be at least #4s at 16" on
center around the perimeter. Start at about 6" from the
corners. They should extend about 6-8" into existing concrete
in the very center of the slab vertically.

In addition and actually more important; Backfill and compact
the area under the new patch/slab. The soils in your area
will determine what is the best way to do that.

--
Robert Allison
Rimshot, Inc.
Georgetown, TX