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RE: Patching small holes in conc. slabs

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Curt---we have done this literally a million times. For holes of about 6
inches up to say 16 inches, we drill in 4 -3/8 diam all-thread rods and set
them with Hilti-HY 150. The drill is set at an angle, as deep into the hole
as practical, and the rods serve as a tie to hold the patch in place.
Embedment is maybe 2 inches max and we use rod cut to have say 2 inch
extension into the hole. Then we drop a piece of plywood in rectangular
shape through the hole, with a hole drilled in the middle, with a loop of
#15 wire through the hole; it takes a dude with thin arms to do this, but he
turns the wood flat and pulls up on the wire to pull it tight to the
underside of the slab, and wraps the wire around a 2x across the top of the
hole. Then, fill it up with whatever patching material is used. In some
cases, we use metal strips in lieu of plywood so as to keep anyone from
having to go up high on the floor below to strip it--we abandon it in place.
That is safe and fast (thus cheap) and in some cases we have left the wood
up is so small an amount as to be deemed not a combustible
hazard. The 2x is removed above, the wire is cut flush to the top of slab
above and presto, the hole is no more. 

Tiny holes (4 inches and less) we usually dam up the bottom with something
(old poly sheet works niceley, but old window screen material works, too)
and just fill it in. That is fast, safe, and thus cheap. We usually check to
make sure enough depth is left in the hole to hold the fire rating
...........Sometimes the dam pops out and there is a lump of concrete on the
floor below in the morning......

Richard W. Stone, P.E.
Project Executive
Technical Services/Project Management/Estimating
Concept Design/Engineering/Quality Assurance
Madison Concrete Construction Company
130 Quaker lane
Malvern, PA 19355-2479
email: rstone(--nospam--at)
Voice:       610.695.8800
Facsimile: 610.695.8678
Nextel:      610.496.5764
Visit our webpage at  !!!!
Subject: Patching small holes in conc. slabs
From: "LaCount, Curt" <Curt.LaCount(--nospam--at)>
To: "Seaint (E-mail)" <seaint(--nospam--at)>

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I was wondering if anyone out there had a clever way of patching small holes
in existing elevated concrete slabs.  The intent is to retain the fire =
and load capacity of an un-cored slab.  Drilling in dowels perpendicular to
the hole face is not practical due to the small dimensions of the hole.  The
dimensions I'm thinking about are from 2" diameter to 12" diameter holes in=
9" thick slab.

Thanks in advance,

Curt R. La Count, P.E.
Structural Engineer
Jacobs Engineering
Portland, OR

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