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Mortar
Joints |
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One
of the more common code violations our inspectors observe in the field
involves the thickness and workmanship of mortar joints in masonry
construction. The purpose of
this article is to assist property owners and construction and inspection
professionals in identifying these common code violations so they may be
corrected. |
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What
is a Mortar Joint?
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1:
Properly-sized and tooled mortar joints in a masonry wall. |
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A
mortar joint is the space between concrete blocks or bricks in masonry
construction.
This space is filled with a compound made of cement, aggregate and
water referred to as mortar.
One of the main purposes of mortar is to act as a bonding agent between
the blocks, holding the wall together.
Another
and often overlooked purpose of mortar is to prevent water from penetrating
through the joints in the wall during heavy rains and flooding.
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Figure
1
shows a masonry wall on a residential property with exposed mortar joints.
Notice how the joints have been properly-sized and the mortar tooled
for a smooth, professional-looking job. The tooling operation helps to
compact the mortar, providing protection against water penetration in areas
subjected to heavy rains and winds.
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Why
are Mortar Joints so important?
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The
compressive strength of a masonry structure depends not only on the brick
being used but also on the type and size of mortar between the bricks.
Thus, a primary component of masonry construction is the mortar itself.
The characteristics of masonry in terms of strength, durability, and
safety result from the properties of the mortar mix as well as other materials
and methods of bonding, joining, anchoring, and the like.
Years ago, masonry
construction referred only to building with stone, but today masonry
construction typically includes manufactured brick, block, and other
materials. Modern masonry
construction in Florida homes often consists of load bearing 8” x 8” x
16” concrete blocks that are available in a range of sizes and shapes.
The
standard weight of the most commonly used concrete block is 40 pounds, which
is made of sand and gravel aggregate. Special shapes for ends, corners,
lintels, and bond-beams are also available with reinforcing rods and tie bars
with grout to increase the strength characteristics of the structure.
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What
does the Code say about Mortar Joints?
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The
thickness of mortar joints is critical to the overall structural integrity of
the dwelling.
As a result, the maximum allowable thickness of mortar joints is
defined in code Section 605.2.1[i]
of the International One- and Two-Family Dwelling Code.
In general, masonry head and bed joints are required to be no more than
3/8 of an inch thick.
The head joint of an 8” x 8” x 16” concrete block is the vertical
8” joint between the two adjoining blocks (when looking at the 8” x 16”
face), and the bed joint is the horizontal 16” joint between the blocks
below and above (also when looking at the face of the block).
Mortar
is a compound ordinarily made of cement, aggregate, and water with a wide
range of workability characteristics largely dependent on the type of cement
and the amount of aggregates used in the mixture.
Special cements such as Portland increase strength while lime increases
“plasticity” along with increasing the incidence of shrinkage that can be
serious, particularly in joints larger than 3/8 inches wide.
Excessive shrinkage can destroy the integrity of the masonry.
The
code specifies the maximum allowable tolerances for mortar joints in Section
05.2.1.1[i]
for load bearing masonry as follows:
Bed
Joints
+/- 1/8 inch
(or: 1/4 inch to 1/2 inch)
Head Joints
-1/4 to +3/8 inches
(or: 1/8 inch to 3/4 inch)
It
is important to note that the code only specifies mortar joint tolerances for
load bearing masonry.
Non-load bearing masonry elements and veneers are often not required to
meet these tolerances.
Additionally,
the code makes an exception for the thickness of the starter course placed
over foundations.
This course is to be a minimum of ¼ inches and not more than ¾
inches.
The variation is allowed to build a level bottom course to start all
those above.
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Common
Violations In The Field
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Mortar
Joints Too Wide
Figure
2
shows the inside view of a poorly laid mortar header joint that well exceeds
the allowable 3/8” width limit established by code.
In fact, this vertical header joint measured more than 1” wide.
As a result, the mortar will dry and shrink, leaving gaps which will
allow water and cold air to penetrate through the wall.
Unfortunately,
mortar joint defects such as this are becoming increasingly common in
today’s residential construction and often go undetected by the new home
owner.
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| Figure
2 - Improper
mortar joint thickness. |
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This
is due in part to the fact that in today’s construction, mortar joints are
covered with stucco on the outside and drywall on the inside, visually hiding
the defects from view.
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Figure
3
shows an outside view of another poorly laid header joint that well exceeds
the allowable 3/8” width limit established by code.
This
header joint not only measured nearly 2” in width, it also had open gaps in
the mortar, allowing visible daylight (and our Inspector’s screwdriver) to
easily penetrate through the mortar joint.
As a result, water and moisture will be able to penetrate through this
wall, which is a common cause of water and wood destroying insect damage in
the near future as the stucco cladding (siding) begins to crack.
Figures
4 and 5 below show the end result of improper mortar joints –
water penetration into
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| Figure
3:
Improper
mortar joint thickness with large gaps due to shrinkage of mortar
between the concrete blocks. |
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a
very expensive custom-built home shortly after the new owner takes occupancy.
This damage could have been avoided by proper mortar joint sizing and
by tooling the mortar between the joints.
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FIGURE
4: “Bubbled paint” and moisture meter readings indicate high levels
of moisture in a wall
due to water seepage through improperly-sized mortar joints. |
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FIGURE
5:
Removal of the plaster wall surface reveals water damaged
elements that could have been avoided by properly-sizing and tooling
mortar joints. |
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Summary
As
we have seen, mortar is a primary component in determining the allowable
compressive stresses in masonry construction. The size of the mortar joint
is important to provide overall masonry strength and protection against
water penetration.
As professional home and commercial property inspectors, we
frequently observe the code violations discussed in this article and
encourage property owners as well as inspection and building professionals
to take the time and effort to identify and correct them.
Therefore,
the conditions discussed in this article should be corrected immediately by
a qualified and licensed contractor.
Please
Contact Us
If
you have any questions, comments or suggestions regarding the information
presented in this article, or if you would like to schedule an inspection of
your property to identify these and other common property defects, please
feel free to contact us directly:
Guardian
Inspection & Information Services |
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E-mail
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info@myguardian.com
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World Wide Web
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www.myguardian.com
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Telephone
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321.639.2743
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Facsimile
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321.636.6377
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Address
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Guardian Inspection & Information Servicesâ
113 Tropic Place
Rockledge, FL 32955 |
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End Notes |
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[1]
International One- and Two-Family Dwelling Code™ 1998, Copyright © 2000
by International Code Council, Inc. Published in cooperation with: Building
Officials and Code Administrators International, Inc., International
conference of Building Officials and Southern Building Code Congress
International, Inc., Incorporated the provisions of the 1995 edition of the
CABO One and Two Family Dwelling Code Promulgated by the council of American
Building Officials (CABO).
NOTICE: The
information presented in this article is intended for educational purposes
only. It is not intended to
identify or predict all the potential defects or conditions that may exist
and be considered for a complete analysis of a given property.
End
of Article
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