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The first impression one gets of a well
maintained building is the way its exterior
envelope looks. Giving the exterior cladding
a face lift when it is needed makes a very
old building look young and attractive and
hence adds to the value of the building and
individual units. Before you undertake any
repairs, you need to consider the following
factors.
Condition Assessment
Before undertaking repairs to the exterior
walls or balconies of a building, a condition
assessment
to
determine
existing
conditions and the nature and causes of
poor performance and visible deterioration,
must be conducted. If this information is
not obtained, there could be a high risk of
the repair failing.The extent of the condition
assessment depends largely on the aims
and objectives of the repair work. The factors
that affect the repair objectives include
safety and structural integrity, performance
and economic service life. Other factors may
include serviceability, appearance and cost.
Cashflow Requirements
A condition assessment of exterior walls
of a building is sometimes required even if
repairs are not contemplated. For example,
a condition assessment may be carried out
as part of an on-going program of monitoring
to establish the performance characteristics
and aging characteristics of the walls. This
information would be useful in projecting
cash flow requirements in a reserve fund
study.
A condition assessment is often limited to
non-destructive
evaluation.
Sometimes
additional destructive investigation, such as
test cuts, is required to confirm or augment
the information obtained non-destructively. A
thermographic scan of the exterior building
envelope may be a useful tool in establishing
the condition of the building envelope.
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Cladding Types
Exterior cladding may consist of brickwork,
precast concrete panels, glazing panels, exterior
drywall and stucco, exterior insulated finished
systems (EIFS), metal siding, wood siding and
other materials, and its performance depends
on good design, correct construction and regular
maintenance.
The two most widely utilized cladding materials
in condominiums/strata, are brick masonry and
exposed concrete.
Exposed Concrete
While concrete has an impressive track record
for durability, as demonstrated by such buildings
as the Pantheon, it nonetheless has properties
that make the development of cracks inevitable
and regular maintenance necessary.
Concrete is a mixture of aggregate and cement
paste; as the cement paste sets and hardens, it
shrinks by as much as 25mm in 30m. While most
of this shrinkage occurs during the construction
of a building, some will occur afterwards. This
means that concrete always cracks; the number,
size and location of the cracks is controlled by
the amount of steel reinforcement embedded in
the concrete and by the number and location of
expansion joints and control joints.
Hardened concrete also deforms. This process
continues for a period of time that is estimated
to be from 5 to 10 years following construction.
Elastic and creep deformation is the gradual
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CCI GROUP
SCIENCE • ENGINEERING • SOLUTIONS
NEWSLETTER
your single source engineering firm
MAINTENANCE..
CONTACT
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(cont.)
compression of concrete under load. It
results in the overall height of a 20 storey
building being reduced by up to 30mm and
in floor slabs deflecting downwards by as
much as 15mm at mid span locations. It will
also cause balconies to deflect towards the
outside edge.
The movement that does occur at the expansion
joint is accommodated by cracks in the walls and
slabs created by drying shrinkage and creep
deformation. This causes the cracks to change
in width between summer and winter.
Floor slab deflection due to creep is a major
cause of the cracks in the exposed concrete
forming the exterior spandrel walls of many
high-rise buildings constructed in the eighties
and early nineties.
Concrete prevents embedded steel from rusting
due to high pH level of the cement paste, but the
presence of salt in the concrete above a certain
threshold level, when activated by water, changes
this pH level and creates conditions that cause
rusting of the reinforcing steel to occur. Since rust
occupies a much larger volume than the original
steel, tensile stresses gradually develop in the
concrete, and eventually the sections of concrete
overlying the rusting bars crack and break loose.
Shortening of the overall height of a building
and deflection of the outside edges of balcony
slabs are important considerations to take
into account when repairing and maintaining
a building envelope.
Both drying shrinkage and creep movement
are irreversible processes with the one being
effectively completed within the first year and
the other within the first five to ten years.
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Temperature and Moisture
Concrete expands and contracts with changes
in both temperature and moisture content.
This movement is mainly accommodated by
expansion joints, but unfortunately expansion
joints often fail to accommodate all of the
seasonal movement that occurs due to
temperature changes, movement that may
be increased by changes in moisture content.
Change in Width
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Salt
Lack of Cover
A similar condition will develop without the
presence of salt at locations at which reinforcing
bars have very little concrete cover, such as
often occurs at shearwalls and floor slab edges,
since under these conditions the cement paste
component of the concrete no longer has
the ability to protect the steel against rusting.
Therefore it is important when repairing concrete
to properly identify the factors causing the cracks
and to design a repair that takes into account the
natural properties of the concrete.
For example, the procedure followed in repairing
cracks due to creep movement should be different
before movement is completed compared to
afterwards. Similarly it is important to take into
account whether cracks are active or passive, are
structural in origin, are due to too little concrete
cover over the reinforcing steel, are caused by
salt in the concrete, or have developed for other
reasons.
Active or Passive Cracks
When repairing cracks, it is important to first
establish whether they are “active” or “passive”.
Active cracks change in width seasonally while
passive cracks do not change in width.
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(cont.)
Passive cracks are normally located either
inside a building where the concrete remains
dry and at a constant temperature or close
to expansion joints which accommodate the
thermal movement.
They also may result from structural distress
caused by impact or overloading.
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Crack Control
The control of cracks in concrete (and
masonry) is achieved by incorporating into a
building control (construction) and isolation
(expansion) joints at pre- determined
locations in floors and walls where cracking or
movement is anticipated. These joints must
be kept sealed against water penetration.
Clear Space or Cavity
Construction joints also occur in concrete
structures between adjacent pours, such as
between floor slabs and shearwalls. These
joints, which normally have reinforcing steel
passing through them, are prone to water
penetration and in floor slabs are weak
locations at which drying shrinkage cracks
develop. They should be kept watertight and
maintained.
Since a single thickness of brickwork is not
watertight against heavy rain, impermeable
flashing is a must in the cavity wall. Located at
the bottom of each panel, the flashing slopes
outward to direct rainwater away from the brick
through holes left in the bottom row.
Brickwork
Brick cladding is the most common cladding
system used in Canada, and for good reason
- it is extremely durable and, skillfully applied,
one of the best protections possible against
the elements. It is also very versatile and
can be used to create either solid, cavity or
veneer wall design.
Solid masonry consists of an inner skin, or
wythe, of concrete masonry and an outer
wythe of brickwork. The two wythes are
connected by metal wall ties and the joint
(collar joint) between them is filled with
mortar. Sometimes brickwork itself is used
to create the bond between the two wythes.
Bricks that occur every sixth course of the
veneer brickwork are turned 90° to extend
back into the inner wythe.
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Cavity walls normally consist of an outer wythe
of brickwork connected to an inner wythe of
concrete masonry with a clear space or cavity
in between.
Veneer is an exterior facing of brickwork applied
to a structural backing. Again, there is a cavity
behind the brick veneer. This makes flashing and
weepholes at the bottom of each panel essential.
The veneer protects the other wall components
from direct exposure to sunlight, wind and
moisture.
A widespread problem in brick clad buildings
is the localized deterioration of brickwork. This
problem rarely occurs in low-rise buildings due
to fundamental differences in the design and
operation of high-rise and low-rise residential
buildings.
There is a potential both for larger expanses
of brickwork to be incorporated into high-rise
buildings and for greater air and water vapour
pressure differentials to exist in high-rise
buildings.
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NEWSLETTER
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MAINTENANCE..
(cont.)
Brickwork only deteriorates in a service
environment that is too severe for its
performance characteristics to accommodate.
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MONTREAL
cracks in the brickwork as well as the gradual
deterioration of mortar in the joints. The
development of vertical cracks often causes
bricks on the line of a crack to break.
Assuming a wall is properly designed,
the masonry constructed to a reasonable
standard and that the materials satisfy the
minimum durability of the Ontario Building
Code, then the major factors that may
singly, or in combination, cause progressive
deterioration of brickwork are:
Maintenance
Differential movement in the brickwork
caused by:
A historic footnote to this aspect of masonry
deterioration is the widespread incidence among
our older brick clad high-rise buildings at locations
at which it is supported on shelf angles for it to
bulge and spall in horizontal lines coincident with
floor slab locations due to absence of horizontal
control joints required to accommodate creep
shortening of the concrete frame of the building,
deflection of the floor slabs at mid spans and
expansion of the brickwork.
•
•
•
•
•
Temperature changes
Moisture changes
Movement of the building frame
Expansion of the brickwork
Cycles of freezing and thawing with the
brickwork in a saturated condition
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Repair the brickwork by the replacement of
cracked bricks and tuck pointing of deteriorated
and cracked joints, and then to create in the
brickwork control joints located as required to
accommodate future movement.
Freezing and Thawing
Bricks subjected to cycles of freezing and
thawing while wet, have a potential to deteriorate
due to the development of cracks. This type of
failure is normally localized and progressive and
is characterized by the bricks separating into thin
slices similar to the cross-sectional appearance
of an onion. For freeze/thaw failure of brickwork
to occur, it is necessary for it to be subjected
to cycles of freezing and thawing while in a
saturated condition.
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Sources of Water
Experience of the Designer
Unfortunately until recently the Ontario
Building Code did not include specific
requirements regarding joint location and
spacing but rather relied on the experience
of the designer. This often resulted in an
insufficient number of joints or incorrectly
located joints.
Thermal movement can result in the
development of both vertical and stepped
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The sources of water available to saturate
brickwork are:
•
•
•
Rainwater
Snow and ice melt water running down over
the face of the brickwork from snow and
ice accumulations perched on window sills,
ledges, balconies and the flat tops of walls
Water vapour or warm humid air exfiltrating
out through the exterior walls during cold
weather
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NEWSLETTER
your single source engineering firm
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(cont.)
Since it does not rain when it is freezing and
vice versa, rain is rarely available to saturate
the exterior face of brickwork during periods
of freezing air temperatures. Rainwater may
however be trapped and accumulate either
inside the voids that are cast into some bricks
as part of the manufacturing process or in the
wall cavity and in this way, be present during
periods of freezing and thawing.
CONTACT
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MONTREAL
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CALGARY
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Melt water from accumulations of snow and
ice perched above brickwork will flow down
and locally saturate the outside face of the
brickwork during periods when ambient air
temperature is fluctuating around the freezing
point and this creates ideal conditions for
deterioration of the brickwork. This is one
reason why brickwork deterioration is often
associated with the areas below windows
and just below the roof.
Another cause of brickwork deterioration
below windows is the condensation of water
on the inside of windows which ponds on
the sills and then finds its way through the
joint between the window sill and the window
frame and into the brickwork just below the
window which could become saturated and
vulnerable to freeze/thaw deterioration.
Deterioration of Inside Face
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Warm humid air exfiltrating out through the
exterior walls of pressurized buildings during
periods of cold weather creates a potential
for condensation of water vapour to occur on
the inside face of the brickwork and this can
lead to freeze-thaw deterioration of the inside
face. Such deterioration is normally limited
in extent and restricted to those locations
where excessive exfiltration is occurring,
thus brickwork deterioration may occur at
the outside face, at the inside face or in the
middle of the brickwork with deterioration
normally being limited to small areas at
typically repetitive locations. Maintenance
can change conditions outside or inside
the brickwork to eliminate the potential for
excessive amounts of water to be present in
the brickwork during periods of cold weather.
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Thermographic Scan
One of the easiest ways of establishing the
extent of deterioration and the locations at which
deterioration is occurring is by utilizing a digital
camera, sensitive to changes in temperature,
known as a thermographic scan.
Essentially the process consists of measuring
the surface temperature of the building envelope
to record variations in thermal radiation. This
process would identify:
•
•
•
•
•
•
Whether thermal insulation requirements
have been met
Cold spots or leakage paths
Effectiveness of different retrofit insulation
techniques
Thermal bridging
Variation in the thermal resistance
characteristics of joints in window assemblies
In response to mildew problems on the interior
of the building envelope, thermographic
scans of the interior surfaces may be carried
out to establish the conditions contributing to
the development of mold.
With older buildings, whose cladding has been
allowed to deteriorate, it may be necessary to
consider other, more drastic, forms of repair,
such as installing a new cladding system. In
adopting this type of approach, consideration
should be given to the installation of a complete
and continuous air and vapour barriers.
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