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RE: Reinforced Concrete Blockwork Construction

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I, too, have designed and inspected masonry projects all over the US and the
world, and I guess my experience and observations are different.  In some
areas of the world (where horizontal rebar in CMU is rare; like the UK),
knock-out units are harder to find.  But in the US the knock-out units are
very common.

For many years the NCMA and the USACE have had details showing the use of
the knock out bond beams  in partially grouted walls. The NCMA and USACE
standard details do not show "U" shaped bond beams except at lintels.  The
NCMA even has a video tape showing the proper installation and grouting
using the knock out bond beams.  

I have seen many jobs where the "U" shaped bond beams are shown on drawing
details, but the masons routinely replace them with the knock out units
without calling the architect or engineer.  Another advantage is that the
masons can replace regular CMU with a knock-out unit, but they can not
replace them with a "U" shaped unit.

The only bond beams used on the west coast are the lintel "U" shaped bond
beams, but the only reason is the predominance of fully grouted masonry
walls.  Where partially grouted walls are the norm, you will see the use of
the knock-out bond beams.

Harold Sprague
The Neenan Company

-----Original Message-----
From: Jeffery Seegert (x 485) [mailto:jbseegert(--nospam--at)]
Sent: Tuesday, July 27, 1999 6:19 AM
To: 'seaint(--nospam--at)'
Subject: RE: Reinforced Concrete Blockwork Construction

In reply to Harold Sprague:

Having been involved with material testing and design of hundreds of
projects around the United States and Canada, I can say that he
predominant block used for installing horizontal reinforcement on the
entire east coast/west coast is bond beam block.  This consists of a
typical 8 x 8 x 16 with a U-shaped profile to place the horizontal steel
in with the normal vertical cells installed to allow reinforcement to be

The installation of fabric or mesh is not considered to be good masonry
practice.  First of all this costs additional money and is never
installed correctly.  This results in an unsatisfactory bonding of the
mortar to the block. Another reason is that it readily allows water to
filter through, thus reducing the volume of the grout which results in
voids.  Typically, the contractor will stuff the cell with paper/trash
which is readily available on a job site. this tends to be satisfactory
enough to prevent any significant leakage.  The best option is to
install the very thin (36 gage) 6 x 6 aluminum cell closures.  These are
sized small enough not to inhibit proper mortar placement.  

Masonry U-shaped lintel block and bond beam block are the same thing.
There also exists a U-shaped precast lintel beam that has become very
popular in the masonry world as it does not require any extended shoring
during the grout curing period (solid bottom; no cell openings).  It is
constructed so as to have vertical openings ( typical cell) on each end
to allow the installation of the jamb reinforcement on each end of the

-----Original Message-----
From: Harold Sprague [mailto:harold.sprague(--nospam--at)]
Sent: Monday, July 26, 1999 6:13 PM
To: 'seaint(--nospam--at)'
Subject: RE: Reinforced Concrete Blockwork Construction

Jeffery Seegert wrote:
"In many areas of the country horizontal reinforcement is installed in
U-shaped bond beam blocks as opposed to concrete tie beams."

In partially reinforced masonry walls few masons will install a bond
unless it is a "knock out" bond beam unit.  The "knock out" bond beams
installed over fabric or lath grout barriers to keep the grout from
into the vertical cells below.  The "U" shaped bond beams are reserved
lintels.  That way you don't have to knock holes into the bottom a "U"
shaped bond beam to run the vertical rebar through.

This detail is shown in the US Army Corps of Engineers "Masonry
Sept 1997, detail 3.1.  I could not find it on their web site.  Although
they do have a detail of the "knock out" bond beam.

Harold Sprague
The Neenan Company

Harold Sprague