There is a section of the concrete wall I would like to pour solid concrete
It is a section that originally was concrete block with a 2" cast iron vent
stack inside. I had to cut the wall with a 6" wide opening to expose the CI
pipe so that I cut fit a snap cutter and cut out an 18" length. I had to do
it because I had to lower the sanitary tee from the kitchen sink so my wife
can have a deep sink and a disposer - the original stub out was too high.
Anyways now it's all done and I think the best way to close it up is to just
pack solid concrete around this 2" pipe.
I can cut a 1x6 and attach them on both sides of the opening to use as forms
for the concrete pour. However I am not sure how I would pour the concrete
in such a tight space to make sure they are packed around the pipe and with
a small opening chances are I will spill a lot of concrete as I try to pour
them in. Should I do it in sections, like add them row by row (6" pour at a
time) or better do it all in one shot?
I had to place concrete around a door opening (8x8 by 80") I built
the form with one open side and closed up the form up, screwing in
wood planks as I went, shoveling in the mud with a big garden trowel.
Tap the form with a rubber hammer as you go and you will get a good
mold to the form. The last lift at the top was open about 4" and I
shoveled all I could before closing that up, 2" at a time. When it was
done I used stucco mix to mud in the last little part I couldn't get.
It was really just a small void.
Use a fairly stiff mix, particularly right at the top. (3-4 slump)
The pressure in wet concrete is sneaky and hard to control if your
form isn't right. The best way to make the form would be to put a
1x6x18" board horizontally on both sides of the wall, then on the
outside of each 1x6, put a 2x2 upright about halfway along the
opening, then get some thick wire (#9 if available) and wrap it around
the far 2x2, over the boards, then on the near 2x2, twist the wire
together tightly, trying to compress the form together if possible. A
bar clamp would be a big help squeezing the 2x2's together while you
twist the wire tight. Fill in the opening with more 1x6 boards placed
horizontally, and every second board on the way up, put in another
piece of #9 wire to hold it all together. The first pour could be
done up to about half way up, the second pour could be done up to 6"
from the top. The very last should be done with a very dry mix,
pressed into place with a small bricklayer's trowel (blade about 5"
long). If this last bit tends to slump out of place, just leave it
for a few hours, then continue. When its basically full, you could
put a layer of mortar over the whole last part, then a few hours
later, using a straight edge and the bricklayer's trowel, shave the
surface down to a nice flat surface. The day after the pour, you can
remove the forms, but don't disturb the wires much for a week.
Concrete achieves 70% of its ultimate strength in a week, so this time
is needed to make a good seal around the wires.
I think the way I would fill in the opening would be to use
concrete blocks as the form to hold the concrete. You can cut block
with an abrasive blade on a skilsaw. Assuming your wall is 8" thick,
cut 5" off each end of an 8" concrete block. You might have to break
these 5" "U" pieces in half to get them in place around the plumbing
drain. Put mortar on the top edge of the previous block, then set the
next piece in place, tapping lightly with a hammer. Hold a straight
edge across your existing wall to see that each new piece is lining
up. When a few courses are hardened into place, fill the voids with
mortar or concrete. Use a jointer tool and your bricklayer's trowel
to fill in any gaps, then about 15 minutes later, use the jointer to
make the decorative groove typical of blockwork.
Tell your wife that I think she's got herself a good man.
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