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Considerations for Repair of Concrete Building Facades

May 15, 2003

10 • Interface March 2003
Building facades constructed of exposed concrete framing elements and
infill windows are common for many high-rise residential, hotel, and institutional
buildings (Figure 1). This results in economical construction and
allows for free expression of the building structure.
When properly designed and constructed, exposed concrete facade elements
can provide a long service life with a reasonable level of maintenance.
Design, construction, and material deficiencies, however, can cause
premature deterioration of the facade elements, necessitating costly repairs.
The most common facade deterioration mechanisms are associated with
cracking due to restrained volume changes in the concrete, corrosion of
embedded reinforcing steel or balcony railing posts, and premature peeling
of protective or decorative coatings. These factors can contribute to water
leakage, air infiltration, poor appearance, and safety concerns from falling
concrete. If not repaired, severe concrete deterioration can also jeopardize
the structural integrity of the building.
This article provides a review of concrete repair methods and materials
for building envelope applications.
Prior to designing repairs to a concrete building facade, several factors
should be considered. These include the following:
Figure 1 – Typical high-rise building facade with exposed concrete structural elements such as slab edges,
columns, and balconies (painted white).
Figure 2 – Cracking associated with extensive corrosion of the vertical
reinforcing bars in a concrete column (approximately 20 stories high).
Kami Farahmandpour,
March 2003 Interface • 11
2.1 Cause and Extent of Deterioration
A proper investigation of the deterioration mechanism and its
extent should be made. Although under most circumstances the
repair methods for spalled and delaminated concrete will be the
same regardless of the cause, the deterioration mechanism and its
extent may dictate a different repair approach in some cases. For
example, if high levels of chloride ions are present in the concrete,
a more aggressive repair approach, such as the use of corrosion
inhibiting materials or cathodic protection measures may be
needed. Also, in most cases, the extent of the deterioration will
have a significant impact on the decision to repair or replace a
component (e.g., a balcony slab).
The most common type of deterioration encountered in
exposed concrete facades is that associated with corrosion of
embedded metals (Figures 2 and 3). The second most common
cause of deterioration in cold climates is the freeze-thaw damage
to concrete elements. Coating failures and leakage through concrete
cracks are also common problems (Figure 4).
2.2 Repair Objectives
Once the cause and extent of deterioration are determined,
repair objectives should be defined. Typically, one or more of the
following will be the objective of the repairs:
• Improving the aesthetics of the building: In some cases,
the concrete deterioration may not impact the structural
integrity, watertightness, or the durability of the facade. If
so, the only objective would be to improve the aesthetics
of the building.
• Restoring durability of building components: In most
cases, the main objective of the facade repair program will
be to restore the durability of the concrete elements and to
significantly reduce the rate of deterioration. It should be
noted that, in most cases where corrosion of embedded
metals is the cause of deterioration, completely preventing
future deterioration is not practical.
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Figure 3 – Concrete spalling at an exposed slab edge due to corrosion of
reinforcing steel.
12 • Interface March 2003
• Restoring structural integrity: If the extent of deterioration
is such that the structure of the building has been
compromised, the main objective of the repair program
will be to restore the structural integrity of the affected
components or the framing system. It should be noted
that most conventional concrete patch repairs are cosmetic
in nature and will not produce composite action with
the structural members. If a structural repair of the concrete
is needed, special provisions for shoring and temporary
removal of all loads from the members should be
• Leakage control: In some cases, deterioration of concrete
will result in unacceptable water intrusion through the
building envelope components. In such cases, repair
objectives will include controlling water leakage. Once
again, due to the nature of the building envelopes with
exposed concrete framing members, complete prevention
of water intrusion is not practical.
2.3 Environmental and Logistical Limitations
Repair design for exposed concrete (especially for high-rise
buildings) should consider the unique environmental and logistical
challenges associated with such work. The following are the
most typical environmental and logistical factors that can influence
specifications for exposed concrete framing elements:
• Wind: High wind on tall buildings can accelerate the drying
of concrete patch materials and pose curing problems.
• Time limitation: On tall buildings, lifting of concrete
patch materials to the repair location with a swingstage
scaffold can take up to 30 minutes. This will shorten the
pot life of many materials that have to be mixed on the
• Lifting repair materials and
lowering debris: Deteriorated
concrete that is removed will
have to be lowered to the
ground. Meanwhile, repair materials
must be lifted to the repair
location, all by scaffolding
equipment that has weight and
size limitations. These factors
can significantly limit repair
options and methods. For example,
the use of shotcrete for
repairs on tall buildings is usually
not practical due to these factors.
• Worker fatigue: Working on
high-rise facades from a
swingstage scaffold while wearing
safety equipment is difficult
at best. In some circumstances,
workers have to remove concrete
from soffits of balconies
and slab overhangs while standing
on a suspended scaffold.
These conditions can cause
worker fatigue and adversely
impact the quality of work. In some cases, repairs that
heavily rely on good workmanship are not possible on a
consistent basis.
• Overhead protection: Performing repairs on a high-rise
building facade will require overhead protection on the
ground. Depending on the height and location of the
building, the overhead protection may have to extend
onto adjacent streets, etc.
• Temporary weather protection: In most cases, removal
and patching of concrete are not practical in the same
day. Therefore, at areas adjacent to windows and other
penetrations, concrete removal and surface preparation
will render the building envelope more susceptible to
water intrusion. Consideration should be given to temporary
• Inconvenience to building owners: Concrete repair techniques
involve the use of chipping hammers and sandblasting
equipment. The use of chipping hammers will
typically cause excessive noise and vibration to be transmitted
through the building frame. The vibration can
result in damage to other building components, such as
interior plaster and adjacent windows. Sandblasting can
also create dust and can cause considerable damage on
the ground if not contained properly. These factors
should be considered during the design process and
should be communicated to the building owners.
2.4 Temporary Support and Shoring
It is common that the exposed concrete elements being
repaired are structural framing members. Therefore, concrete
removal around the reinforcing steel will reduce the structural
capacity of the member. In high-rise buildings, significant
removal of concrete from columns without due consideration to
Figure 4 – Coating failure on a concrete shear wall on a high-rise facade.
March 2003 Interface • 13
the structural integrity of those columns can have catastrophic
results. Also of importance are removing portions of balcony
slabs and removing concrete from slab overhangs adjacent to
columns where significant shear transfer occurs (Figure 5).
Therefore, it is important that the anticipated location and
extent of concrete removal be reviewed by a qualified structural
engineer prior to specifying repairs. Of course, concrete removal
should also be carefully monitored during repairs to avoid the
same issues.
2.5 Cost Versus Service Life
Like most things in life, longer lasting repairs can cost more.
Features that enhance concrete repairs, such as protective coatings,
sealers, corrosion-inhibitors, and cathodic protection can
add significant cost to repairs.
However, due to the high access
costs for building facades, the
additional service life realized will
typically offset the initial cost.
2.6 Selection of Repair
Proper selection of repair materials
is a critical step toward the
successful repair of concrete.
Experience has shown that materials
that are not compatible with
concrete can fail prematurely, even
if the repair material characteristics
are superior.
One of the most important
materials used in the repair of concrete
is the patch material itself.
Experiences with epoxy and other
resin-based materials have not
yielded favorable results. Currently,
the state of the art in repair
materials is more conventional proprietary
cementitious repair mortar
that contains various additives to
improve performance. Among the
advantages of the proprietary repair mortars are the exact proportioning
provided by the bagged materials and better quality
control. In addition, such bagged materials are more suitable for
use on high-rise facade repairs where, typically, small quantities
of repair mortar are used at one time.
The most common additives found in repair mortars are
corrosion-inhibiting admixtures (to reduce the potential for
future corrosion of reinforcing steel), shrinkage-compensating
materials (to reduce the potential for shrinkage cracking), polymer
modifiers (to reduce permeability and increase bond
strength to substrate), and accelerators or retarders (to control
material set time).
Although sophisticated proprietary repair mortars have been
used successfully in the past, conventional concrete materials
have also yielded excellent performance for the past several
years. Conventional concrete mixes (typically provided by a
ready-mix truck, in bags, or mixed at site) offer the advantage of
lower cost and better suitability for high-volume applications.
When selecting a repair mortar for a particular application,
one should consider the following attributes of the material:
• Compressive strength and modulus of elasticity: It is
desirable to specify repair materials with compressive
strength and modulus of elasticity similar to those of the
substrate material. This is more critical when performing
structural repairs where the patch material will act compositely
with the remaining section of the member.
• Bond characteristics: Durability of concrete patches
greatly depends on their bond to the substrate material.
Therefore, careful consideration should be given to the
ability of the repair mortar to bond to the substrate material.
• Shrinkage: Another important factor in the durability and
performance of a patch is the material’s shrinkage potential.
When placed in the confines of a concrete member
that has undergone most of its drying shrinkage, any
shrinkage of the repair mortar will result in cracks that
can adversely impact its durability.
• Permeability: If the repaired areas of concrete are susceptible
to airborne chlorides (such as on buildings along
coastal areas), lower permeability repair materials will be
desirable to reduce the rate of chloride migration to the
reinforcing steel. Lower permeability of the repair materials
is also desirable to slow the rate of water penetration
into the repaired area and the reinforcing steel.
• Corrosion protection: The selected repair materials
should provide adequate protection against future corrosion
of the embedded reinforcing steel and adjacent areas.
Some of the proprietary repair mortars available on the
market today incorporate corrosion-inhibiting admixtures
Figure 5 – When removing concrete at slab-column interface, shear transfer at the connection should be considered.
14 • Interface March 2003
for this purpose.
• Coefficient of thermal expansion: The repair material’s
coefficient of thermal expansion should be similar to that
of substrate material. Lack of compatibility of the coefficients
of thermal expansion can lead to the development
of high stresses along the bond line between the patch
and the substrate and may ultimately result in failure of
the patch.
• Resistance to freeze-thaw deterioration: In colder climates,
exterior building elements can undergo several
freeze-thaw cycles each winter. Exposed balcony slab
edges and overhangs are particularly susceptible to such
deterioration. Therefore, the selected repair materials
should possess good resistance to freeze-thaw deterioration.
• Aggregate size: The aggregate size used in the repair
mortar should be compatible with the patch geometry.
Most proprietary patch materials are formulated with fine
aggregate only (sand). The use of such materials in large
patches will result in excessive shrinkage, which in turn
can lead to cracking of the patch. For this reason, most
repair mortar manufacturers will indicate a maximum recommended
application thickness for their products.
Conversely, large, coarse aggregate particles are not suitable
for small repairs where patch thickness is low or the
clearance between the reinforcing steel and the substrate
concrete is small.
• Workability and set time: The workability of the repair
mortar should be consistent with the placement methods
used. For example, if the dry patching method is used for
placement, a stiff material is desired. On the other hand,
when the form-and-pour method is used, a more flowable
material should be used to facilitate consolidation. Setting
time can also be an important consideration, since the
repair materials are typically lifted to the patch location
via scaffolding after they have been mixed on the ground.
• Appearance: Although most patched areas are ultimately
covered with a decorative coating, some concrete patches
will be left uncoated. In such cases, the texture and color
of the patch will have to resemble adjacent materials.
Some patch-repair mortar manufacturers offer custom
blending of their products with color pigments.
When selecting repair materials, consideration should also be
given to the need for bonding agents. In the author’s experience,
the popularity of bonding agents has diminished over the years.
This may be due to the marginal benefits gained by the use of
bonding agents, the limited number of failures due to their misuse,
and the improvement in bond value between state-of-the-art
repair mortars and the substrate concrete.
The purpose of a bonding agent is to improve the bond
between the repair mortar and the substrate concrete. Most common
types of bonding agents include cement slurry, epoxy resin,
and polymers. Although all these types of bonding agents can
improve bond values between the repair mortar and the substrate,
there is no substitute for proper surface preparation and
application practices. The misuse of bonding agents can also
lead to bond failures. For example, if an epoxy bonding agent is
used prior to erection of the formwork and sufficient time elapses
before the repair mortar is placed, the epoxy bonding agent
can harden and become a “bond breaker.” For this reason, if a
bonding agent is specified, consideration must be given to its
application method, set time, etc.
Another repair material that needs to be selected properly is
the corrosion protection coating on the reinforcing steel members.
Various protective coatings include zinc-rich coatings,
cementitious coatings, and epoxy coatings. All of these have
shown various degrees of success. Each has advantages and disadvantages.
The selection of the reinforcing steel coatings
should depend on compatibility with other repair materials, ease
of application from a swingstage, curing time, and level of corrosion
3. Patching techniques and materials
Over the years, several repair methods have been used by the
concrete repair industry. Based on the observed success of such
repairs, the following repair techniques and sequence have
3.1 Identifying Delaminated Areas and Extent of Required
Concrete Removal
Delaminated concrete on building facades is typically identified
using a hammer tapping method. Although a trained worker
can easily identify delaminated or unsound concrete with the
hammer tapping method in the great majority of cases, identifying
deep delaminations or voids in concrete may require more
sophisticated methods, such as those described in Reference 1.
Once the delaminated areas are identified, they should be
marked immediately so that they can be verified by an engineer,
architect, or qualified inspector.
3.2 Concrete Removal/Rough Demolition
Once the delaminated or unsound areas of concrete are identified,
the concrete in the affected areas should be removed. On
high-rise facade repair projects, concrete removal is typically
performed using pneumatic chipping hammers. The use of chipping
hammers in excess of 15 pounds is typically avoided in
order to prevent excessive substrate bruising. Substrate bruising
can occur when chipping hammers cause microcracking of the
sound concrete. Excessive microcracking results in a weakened
concrete zone along the bond line, where bond strength is crucial.
Concrete removal should always extend into sound concrete
without excessive removal of sound areas. In most cases, the
extent of concrete removal can be determined only during the
rough demolition process. An experienced worker should be able
to adjust the patch geometry depending on what is found during
concrete removal. In some cases, lightly corroded reinforcing
bars can be encountered several inches past the perimeter of the
delaminated area. In these instances, the affected areas should be
removed until clean reinforcing steel is encountered. Current
industry standard practices dictate that concrete be removed
around the entire perimeter of corroded reinforcing steel so that
the affected rebars can be completely encapsulated in repair
Concrete removal should be performed so that large variations
in patch depth are avoided. Also, the overall geometry of
March 2003 Interface • 15
the patch should be simple (i.e., square, rectangular, etc.) with
no re-entrant corners. The patch geometry has a significant
influence on cracking of the repair mortar and its durability.
3.3 Saw Cutting Patch Perimeter and Surface Preparation
After the rough demolition process, the perimeter of the
patch should be well defined by saw cutting around the entire
perimeter of the patch. The saw cut will provide a straight edge
for the repair mortar to bond to the substrate concrete and will
prevent feather-edging the repair mortar. The depth of the sawcut
is typically 1/2 inch; however, the depth of saw cut should
be reduced where reinforcing steel is encountered.
On small patch areas where mechanical anchoring of the
patch with reinforcing steel is not used, the saw cuts should be
made at a slight angle to form a dovetail shape for the patch
(Figure 6). This will mechanically lock the repair mortar in place
and prevent spalling if a loss of bond occurs.
Surface preparation of the substrate concrete should include
removing all damaged and unsound concrete that is left by the
rough demolition process.
3.4 Reinforcing Steel Repairs
Since most concrete repairs on high-rise facades are necessitated
by reinforcing steel corrosion, repairs to the reinforcing
steel are typically needed. At a minimum, reinforcing steel
repairs should consist of removing all corrosion products around
the entire perimeter of the affected bars.
This is typically performed using sandblasting
or water blasting methods.
However, in some areas where sandblasting
or water blasting causes containment
problems on the ground, wire brushing
using power tools may also be used.
Regardless of the method used, cleaning
of the reinforcing steel bars should
render them completely free of corrosion products.
If reinforcing steel corrosion has resulted in
significant loss of bar diameter, a qualified structural
engineer should review the patch area and
determine if there is a need for supplemental
reinforcing. Where supplemental reinforcing is
required, it can be coupled to the existing bars
using mechanical couplers or simply lapped
adjacent to the affected bar.
In some cases where re-bar congestion in the
patch will prevent proper placement and consolidation
of the repair mortar, some bars should
be removed. Once again, a qualified structural
engineer should determine whether selective
removal of reinforcing steel will have an impact
on the structural integrity of the member.
Since most concrete repairs do not act compositely
with the existing member, supplemental
reinforcing steel may be unnecessary in some
cases. However, supplemental reinforcement is
typically added to provide mechanical anchorage
for the patch (Figure 7). This is done so that
if a loss of bond between the patch and the substrate concrete
occurs, it does not result in spalling of concrete from the facade,
a serious safety issue.
Supplemental reinforcing is typically installed in substrate
concrete using adhesive anchoring systems. Where supplemental
reinforcing is used merely as mechanical anchorage for the
patch, it can consist of 1/4-inch-diameter stainless steel threaded
bars that can be bent and formed easily on a swingstage.
After completion of reinforcing steel repairs and installation
of supplemental reinforcement, a corrosion-inhibiting coating is
Figure 6 – Small patch area.
Note the perimeter saw cut has
been dovetailed to lock the patch
material in place. Also, the
depth of saw cut has been
reduced due to shallow concrete
cover at the reinforcing steel.
Figure 7 – Stainless steel supplemental reinforcing steel installed at a repair location.
16 • Interface March 2003
typically applied over the exposed steel bar surfaces. The most
common reinforcing steel coatings consist of epoxy coatings,
zinc-rich coatings, and cementitious coating. Care should be
taken to avoid the application of the re-bar coating on substrate
surfaces, as it can serve as a bond breaker. Care should also be
taken to ensure that the entire perimeter of affected bars is coated
properly. A routine check of coating application should be
made with an examination mirror to inspect areas that are not
Another consideration in performing reinforcing steel repairs
is the possibility of galvanic corrosion. For this reason, contact
between dissimilar metals should be avoided.
3.5 Final Preparation
The final preparation of the patch cavity should consist of
cleaning and roughening the concrete substrate and making final
adjustments to the patch cavity geometry. This step is usually
performed in conjunction with cleaning of the embedded metals
using sandblasting or water blasting methods. Note that sandblasting
or water blasting of the patch cavity cannot be performed
after application of corrosion-inhibiting coatings on the
reinforcing steel.
If additional corrosion protection is planned, such as application
of migrating corrosion inhibitors or passive cathodic protection,
it should be performed at this stage.
3.6 Forming
Currently, the majority of concrete patch repairs on high-rise
buildings are placed using the form-and-pour method (Figure 8).
This includes almost all of the patches placed on horizontal surfaces
(such as balcony and overhang top surfaces) and vertical
surfaces (such as columns and walls). In some cases, repairs made
to slab soffits are also placed using the form-and-pour method.
This is accomplished by drilling one or more core holes through
the entire slab thickness to facilitate placement from the top. In
such cases, the patch geometry should be considered carefully to
avoid creating trapped air pockets in the patch.
In a few isolated cases, the repair mortar is placed by forming
the cavity and pumping the repair mortar from the bottom of the
formwork. Although this method is less practical due to its logistical
requirements, it does provide certain advantages over conventional
placement methods.
Unless the repair mortar is placed using a drypack or shotcrete
method, the repair cavity should be formed. Forming of the
repair cavity is typically similar to conventional concrete placement.
When forming patches on vertical surfaces for conventional
placement (pouring), openings (birds’ mouths) should be
formed at the top of the patch. When forming for placement
with pumping method, openings at the top and bottom of the
patch should be made. Depending on the patch geometry, forms
should be supported using post shores and other supplemental
Figure 8 – Forming of a concrete column patch.
March 2003 Interface • 17
3.7 Substrate Wetting, Patch Placement, and Finishing
In order to achieve optimum bond between the substrate and
the repair mortar, the substrate should be saturated surface dry
(SSD). Therefore, the patch cavities should be wetted prior to
placement of the repair mortar to saturate the substrate.
However, sufficient time should elapse before placement of the
repair mortar to achieve surface dry conditions. Repair mortar
should then be placed in the cavity or formed areas. If the drypack
method is used, placement should be followed immediately
with finishing of the patch surfaces. In some cases, dry-packed
patches can be stamped to match the adjacent surface texture.
3.8 Curing and Form Removal
All cementitious materials require proper curing for optimal
strength gain and for reduction of the cracking associated with
drying shrinkage. In the case of small concrete patches, such as
those on building facades, curing takes on a more important role.
This is due to the higher potential for a confined patch to develop
shrinkage cracking.
The curing process should prevent evaporation of moisture
from the repair mortar surface (thus reducing shrinkage cracking)
before the material gains sufficient strength to resist cracking. In
some cases where materials are placed in colder climates, the
curing process should also prevent exposure of the repair materials
to low temperatures (typically lower than 40 degrees F).
Typically, properly coated plywood forms can provide adequate
protection for patch surfaces that are not exposed to
severe climates. After removal of the forms, plastic sheets or an
appropriate curing compound should be applied over the patch
surfaces to prevent rapid drying. If a coating is to be applied
over the patch surfaces, the use of curing compounds should be
avoided. If curing compounds are used, they should be removed
from the surface later by grinding or sandblasting. In all cases,
the patch material manufacturer’s recommendations for curing
duration and methods should be followed.
3.9 Surface Grinding
After curing, patch surfaces should be inspected for imperfections.
Bugholes and voids should be filled with a cementitious
mortar. Grinding of the patch is usually needed around the
perimeter to provide a smooth transition between the patch surface
and adjacent concrete.
3.10 Coating Application
Since replicating the color and texture of existing concrete is
not practical in most cases, repaired concrete surfaces on highrise
facades typically receive an application of coating to provide
a uniform appearance. In addition to aesthetic advantages, some
coatings will also provide resistance to carbonation and decrease
surface permeability of the concrete (making it less likely to wick
water). Coatings alone should not be depended upon to provide
waterproofing on concrete surfaces. However, the author
acknowledges that there are several coating systems designed for
application on concrete facade surfaces that are marketed as
“waterproofing coatings.” These materials have exhibited varying
degrees of success in imparting a waterproofing characteristic to
the concrete surfaces.
Coatings for concrete facade surfaces should be selected
carefully, taking into consideration the following factors:
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18 • Interface March 2003
• What is the purpose of the
coating – i.e., to provide waterproofing,
to improve aesthetics,
• Are there any existing coating
systems that will remain on the
• What is the permeability of
the new coating system, and will it
allow adequate vapor transmission?
• What are the application
limitations of the coating – i.e., temperature
limits, required substrate
moisture conditions, curing, etc.?
The most popular types of coating
systems for concrete facades
include rigid acrylic coatings, elastomeric
coatings, and cementitious
coatings. The use of elastomeric
coatings for bridging of cracks
should be avoided. In most cases,
visible cracks should be routed and
sealed with an elastomeric sealant
prior to application of the coating,
except where cracks have been
demonstrated to be non-moving (dead). However, caution
should be exercised when applying a coating over sealant. If the
sealant and coating are not compatible, migration of plasticizers
from the sealant into the coating will result in staining of the
4. Repairing Cracks in Concrete
In general, all visible cracks on a barrier type concrete facade
should be routed and sealed. If not sealed, these cracks can lead
to water penetration to the building interior or to the reinforcing
Routing of the cracks will create a reservoir that will allow
proper movement of the joint without imparting undue stresses
on the sealant (Figure 9). The bottom surface of each sealant
reservoir should be treated with a bond breaker to avoid threesided
adhesion. Compatibility of the sealant with the concrete
coating system should be checked before selecting the sealant.
In some cases, silicone sealant extrusions can be utilized for
covering cracks. However, their use will typically make the
cracks more visible, even after application of a coating.
Other methods of crack treatment include injection with
epoxy or chemical grout and application of a coating system that
can bridge the crack. The author recommends that the use of
these methods be limited to cracks that have been demonstrated
to be non-moving.
More information on repair of cracks in concrete can be
found in Reference 2.
5. Quality Assurance
Longevity of concrete patch repairs on high-rise facades
greatly depends on good workmanship and successful implementation
of each of the steps indicated in Section 3 of this article.
Therefore, quality assurance at various stages of the work is
essential for durable repairs.
Figure 9 – A routed crack prior to installation of the backer rod and sealant.
March 2003 Interface • 19
Typically, an inspection of each repair area is performed at
the following stages of the work:
1. Initial sounding and identification of the patch area: A
qualified engineer or inspector should verify that the
workers have properly sounded all concrete surfaces and
identified delaminated areas.
2. Rough demolition: An inspection is made after completion
of the rough demolition to ensure that all unsound
materials have been removed, to check the geometry of
the patch, and to ensure that no further deterioration
exists beyond the patch perimeter. At this stage, the need
for supplemental reinforcing should be evaluated, and the
contractor should be advised as to the location and number
of supplemental anchors if not already shown on
3. Final surface preparation: After completion of the surface
preparation and immediately before placement of
forms, an inspection should be made to verify installation
of supplemental reinforcement, cleaning and coating of
existing reinforcing steel, and surface preparation of the
substrate material.
4. Form removal: After removal of forms and initial curing,
another inspection should be made. At this stage, all
patch surfaces should be checked for cracking and proper
consolidation and sounded to detect delaminated areas.
All defects should be marked for correction. At this stage,
all remaining cracks to be routed and sealed (and all
patch surfaces requiring grinding and filling of bugholes)
should also be marked.
5. Final inspection: A final inspection of the repairs should
be performed after completion of crack repairs and coating
application to ensure proper application of the coating
and crack repairs.
6. Special Issues for Facades
There are a number of issues that can pose significant difficulties
when performing repairs on concrete facades.
In some cases, deterioration on slab extensions can extend
into the building interiors. In such cases, concrete repairs will
have to be performed inside the building, a significant inconvenience
for most buildings.
Performing the repairs can cause significant inconvenience to
building occupants and adjacent buildings. These inconveniences
include noise, vibration, dust, and in some cases, window breakage.
Most concrete frame buildings requiring repairs are 20 to 40
years old. In some cases, repairs are performed on building components
that have been repaired once or twice in the past.
Although some repairs are necessitated by improperly performed
past repairs, most are needed due to reinforcing steel corrosion
spreading around the perimeter of previously repaired areas. This
phenomenon is commonly referred to as the “Ring Anode Effect”
or the “Halo Effect.” Ring anode corrosion is an electrochemical
phenomenon driven by changing electrochemical properties
between the patch material and the original concrete. These differences
in electrochemical properties of the materials cause
accelerated corrosion rates outside the perimeter of the patch.
Eventually, corrosion can be driven to the interior of the building,
making it much more difficult to repair.
Recent advances in reducing or preventing ring anode corrosion
(and corrosion of reinforcing steel in general) include the
introduction of passive cathodic protection and migrating corrosion-
inhibitors. A detailed discussion of these preventive measures
is beyond the scope of this article. Several studies are
currently underway to evaluate the long-term effectiveness of
these measures. It is likely that a definitive conclusion regarding
the effectiveness of passive cathodic protection and migrating
corrosion inhibitors will not be reached for a few more years. 
The author acknowledges and appreciates the assistance provided
by Kristin O’Connor and Johanna Tuozzo in preparing
this article.
Suggested Reading Material
1999 Concrete Repair Manual, International Concrete Repair
Institute (ICRI), Des Plaines, IL, 1999.
ACI Committee 546, “Concrete Repair Guide (ACI 546R-96),”
American Concrete Institute, Farmington Hills, MI, 1996.
Emmons, P., Concrete Repair and Maintenance Illustrated, R.S. Means
Company, Inc., Kingston, MA, 1993.
1 Farahmandpour, K., Jennings, V., Willems, T., Davis, A.,
“Evaluation Techniques for Concrete Building Envelope
Components,” Proceedings of RCI Building Envelope Symposium,
Seattle, WA, 2000.
2 ACI Committee 224, “Causes, Evaluation, and Repair of
Cracks in Concrete Structures (ACI 224.1R-93),”
American Concrete Institute, Farmington Hills, MI, 1993.
Kami Farahmandpour is the
principal of Building Technology
Consultants, a forensic engineering
firm specializing in the evaluation
and repair of building envelope problems.
Over his 18-year career in the
construction industry, he has managed
over 250 projects involving the
evaluation and repair of building
components. Mr. Farahmandpour is a
licensed Professional Engineer,
Registered Roof Consultant, Certified
Construction Specifier, and Certified Construction Contract
Administrator. His expertise is concentrated in the area of
building envelopes. He has performed numerous evaluations of
concrete and masonry facades and roofing and waterproofing
systems. Kami is an active member of several professional
organizations, including the Roof Consultants Institute, the
International Concrete Repair Institute, and the American
Concrete Institute. He has authored a number of articles on
building envelope evaluation and repair and has served as a
regular speaker for the Portland Cement Association’s
Concrete Repair courses for the last several years.