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Synthetic Stone Veneer How to Avoid Problems

May 15, 2007

Stone has been used as a building
material since the Stone
Age and, unlike that period, it
will not be an extinct construction
material anytime
soon. While natural stone is
used in all aspects of home construction
such as exterior wall claddings, in the early
1960s, companies began manufacturing
synthetic or “fake” stones that replicated
natural stones. Advancements in technology
throughout the years have created more
authentic artificial stones that continue to
replace natural stones for use as exterior
wall claddings.
Without advocating on behalf of the synthetic
stone industry, the products it manufactures
offer many advantages over natural
stone. Advantages include lower cost,
greater availability, a wide variety of colors
and styles, lighter weight, quicker installation
time, small waste factors due to custom
pieces such as corners and water tables,
repeatability, and reliability for the construction
trades installing the products.
Regardless of the quality of the product
used to “skin” a building, the quality of any
exterior cladding ultimately depends on the
quality of installation. This article will
attempt to provide the information needed
to ensure that stone veneer and related
building components do not suffer failures
related to improper installation and lack of
detailing at important locations.
Why Problems Occur
If stone has been around and used as
an exterior wall cladding for thousands of
years, why have there been problems with it
only recently? Water is the catalyst for nearly
all problems associated with exterior wall
claddings, including stone veneer. While the
amount of rain and snow has not changed
significantly through the years, the ability
of a structure to “get wet” and allow for drying
of the materials (moisture reservoir)
has. In the past, homes were not built utilizing
airtight methods, nor were they insulated
very well, and therefore they were not
very energy efficient. However, the advantage
of this old system was that it allowed
wet building components to “dry out” without
damage.
The current emphasis on energy-efficient
homes has created much “tighter”
building envelopes, utilizing better air barriers
and increased levels of insulation. In
addition, the materials used to build these
homes have also changed and become more
susceptible to water damage, in many
instances providing food for fungal growth.
The increase in “tightness” and change in
materials has led to a decrease in the building
envelope’s ability to absorb water and
“dry out” without damage. Therefore, the
industry’s previous methods of installing
exterior wall claddings such as stone with a
drainage cavity or stone thickness that
allowed a moisture reservoir must change
and adapt to trends in the industry. This
way, one can effectively control water and
ultimately have a satisfied end user, avoiding
costly damages and callbacks.
Unfortunately, the increase in water
related problems associated with exterior
veneers is not limited to an increase in the
building envelope’s “tightness” or a change
in materials. Consider the following:
1. Stone application is no longer a
skilled craft. Due to budget constraints
and improperly used “value
engineering,” builders and developers
will commonly award contracts
to the lowest bidder. These low bidders
generally do not lower their
price based on material cost, which
should be relatively similar among
all bidders. Instead, they employ the
cheapest labor available and reduce
or eliminate supervision of the
installation and review of the drawings,
specifications, and other requirements.
If the labor pool is not
educated as to proper installation of
the product, the result may be an
unsatisfied client.
2. Lack of information. Many stone
manufacturers currently do not
publish adequate details to properly
install the stone at terminations and
other components. Additionally,
many projects employ a “builder’s
set of plans,” in which only a know-
A U G U S T 2007 I N T E R FA C E • 1 3
ledgeable builder can determine the
remaining details and coordinate
this information to the subtrades on
the project. Unfortunately, this
means the detailing is often left up
to the laborer in the field.
3. The language barrier. If English is
not the primary language of many of
the applicators, training then presents
a problem that companies
must consider. Even if the applicators
possess a genuine concern and
an “old-school” pride in their work,
updated requirements and changes
in waterproofing techniques may
prevent them from installing the
stone as instructed because of language
barriers. Moreover, laborers
may not be provided a meaningful
way of presenting questions due to
fear of retribution or perceived
incompetence. One method that can
help to overcome the language barrier
is to supply adequate illustrated
details that can greatly assist the
applicator in properly installing the
product.
4. Lack of supervision. Too often, the
project superintendent will simply
rely on the “stone guys” to get it
right. And although upon completion
of the project any installed
stone veneers appear to be aesthetically
functional, the performance of
the system is set for failure. The
general contractor needs to set
supervision roles at a level that is
consistent in order to provide the
correct end product and not base
oversight around the possible profit
of the job.
5. The slipping standard of installation.
This basically summarizes all
the points above. “Value engineering,”
lack of quality information and
details, unskilled workers, the language
barrier, and a lack of supervision
all result in a reduced standard
of installation and stone veneer
application with greater susceptibility
to problems down the road.
So now that we know why these problems
can occur, how can we avoid them?
How To Avoid Problems
We will attempt to break down the application
of synthetic stone veneer from the
sheathing to the weatherproofing systems.
With the proper information provided, field
superintendents and stone contractors can
utilize this article and details when observing
or supervising applicators to avoid costly
callbacks and, possibly, court time.
It is important to point out that waterproofing
details
and characteristics
of synthetic stone
veneer are functionally
similar to
those of traditional
stucco. The waterproofing
details for
stone should be
better than those
for stucco because
the outer face of
the stone field will
generally allow a
greater amount of
water to reach the
building papers and, therefore, the discharge
points will need to handle greater
quantities.
At a minimum, stone installation should
be treated in a manner similar to stucco.
Stucco systems are not immune to waterrelated
problems when they are installed
improperly. However, there is currently a
greater amount of information on stucco
that is easily available for detailing and
installing in a weather-tight manner. That
information is also useful for stone
installers, designers, and contractors.
Weather-Resistive Barrier and Drainage
Plane
The installation of the weather-resistive
barrier and drainage plane over the sheathing
is the most important step in the application
of stone veneer to prevent moisture
intrusion issues. Before any wire lath (and
certainly stone) is applied, a thorough and
detailed review of the weather barrier
should be performed. Do not assume the
laborers in the field who installed the paper
have taken the necessary steps to ensure
the building is weatherproof. The building
should function fully at this stage without
veneer being installed; that is, the building
is weathertight without stone veneer, as
flashings will direct water to the exterior.
Here are some helpful hints to avoid
costly repairs. It will save a lot more money
to do it right the first time than to fix the
building after the fact.
• Material selection: Currently, two
layers of Grade D Kraft building
paper (20-minute rating) is acceptable
as the weather-resistive barrier
behind adhered stone veneer. Our
firm has observed multiple projects
in which this weather-resistive barrier
material does not hold up well
behind adhered stone veneer and
cannot handle repeated wetting and
drying.
There is a growing concern in the
building envelope industry that
Grade D paper disintegrates with
repeated wetting and drying. With
synthetic stone veneer (especially
the dry-stack installation method),
more incidental water typically
reaches the underlying weatherresistive
barrier than is true with
stucco systems. This is due to the
increased amount of separations in
the grout between individual stones
(the dry-stack method does not
include grout at all) and the lack of
proper sealant joints at terminations
(to be discussed later). Use caution if
selecting and applying Grade D
building paper behind adhered
stone systems. Using building felts
or a combination of polymeric
housewraps with building paper
may withstand repeated wettings
and dryings better than Grade D
paper.
• Use a minimum of two layers of
building paper or properly selected
housewrap. The first layer, considered
sacrificial, can bond to the
scratch coat and lose its waterproofing
ability or deteriorate altogether
(see above). The second layer is the
actual waterproofing layer.
• Water flows downhill when not
restrained by other forces. Water will
flow in a downhill direction on the
14 • I N T E R FA C E A U G U S T 2007
WATER IS THE CATALYST FOR NEARLY
ALL PROBLEMS ASSOCIATED WITH
EXTERIOR WALL CLADDINGS,
INCLUDING STONE VENEER.
weather barrier. Make sure the
weather barrier is installed to shed
water onto the lower layer. It is surprising
how often installers start
applying building paper from the top
down. Again, don’t take this simple
issue for granted.
• Watch the windowsills. Many times
when a project comes to our attention
as forensic engineers, our job is
to determine if there’s a problem
with the stone veneer and any related
damage. Generally, the first place
to review and inspect is behind
stones at the corner of an exposed
windowsill. Damage found is often
directly related to paper that is
reverse-lapped at the windowsill,
which allows water to penetrate the
stone layer and flow behind the
paper against the sheathing.
An easy way to avoid this problem is
to wrap the building prior to the
windows and doors being set. Wrap
the paper into the rough opening,
using a self-adhering, modified bitumen
flashing tape at the sill rough
opening, and then set the window.
(If this is done, watch the weather
barrier at the window head to make
sure it is not lapped behind the window
frame. When a client complains
about window leaks originating from
the head, this condition of reversed
head flashing is usually why.)
In many jobs, the sequencing of the
trades requires that
the contractor
install the windows
prior to the building
paper to get the
building “dried in.”
The window installers
typically
apply their flashing
tape around the
window, setting the
stage for a future
flashing back-lap
below the window.
However, measures
can still be taken to
ensure there is a
proper weather barrier
application at
the windowsill if the
windows are set
first. Strips of building
paper slightly
wider than the rough opening
should be cut. Self-adhering modified
bitumen (SAMB) should be
applied into the rough opening and
the cut section of paper should be
attached to the SAMB (see Figure 1).
When the rest of the weather barrier
is applied, it can be easily integrated
with the cut section of paper in shingle-
lap fashion.
• Flashings are an integral component
of the weather barrier and drainage
plane. The building paper and flashings
must all be integrated to shed
water onto one another and eventually
out of the system. This includes
both sheet metal “Z”-type flashings
and membrane-type flashings.
Apply the knowledge that a drop of
water should flow freely from the
roofline to the foundation wall. If
any areas are constructed that allow
water the avenue to travel behind
the weather paper, they should be
corrected.
• Coordination between trades is also
important. Typically, homes have
more than one type of exterior
cladding material installed. Therefore,
problems often occur where the
two claddings interface. Too often, a
reverse lap or gap occurs in the
weather barrier behind the interface.
An easy way to avoid this is to
have only one contractor apply the
entire weather barrier around the
building. That way, there’s only one
trade whose work has to be inspected.
This also reduces finger pointing
later. Another successful method is
cutting a strip of building paper
about 12 inches wide and attaching
it to the sheathing where the two
Detail 1
Figure 1: Examples of precut sections of building paper under windows to ensure
proper lapping.
Figure 2: The consequences of reverse lapping.
A U G U S T 2007 I N T E R FA C E • 1 5
claddings interface. That way, the
paper from the cladding below the
interface can be slipped up behind
the precut piece, similar to the window
situation previously mentioned.
Make sure that the trade knows the
intent of the precut paper.
• Don’t forget about the penetrations.
A good idea is to strip in the penet
r a t i o n s
with SAMB
so they are
sealed to
the weather
barrier.
The building
should be weathertight,
even without
any exterior
cladding applied.
After the weather
barrier has been
applied and windows
installed,
imagine a heavy rainstorm occurring. Will
any water be able to reach the OSB sheathing?
Will any water be able to enter the
building? If the weather barrier is applied
correctly, all of the water should stay on the
weather barrier and shed over the sloped
horizontal flashing leg, over the drip leg of
the flashing, and away from the building.
Do not move forward until it is absolutely
certain that the building is weatherproof
without any wall cladding. Once the stone is
applied, the weather barrier is covered,
along with any reverse laps, voids, etc.
Again, it’s much more expensive to find and
correct problems later with the weather barrier,
so get it right the first time.
Trim Accessories
Trim accessories for stone? As discussed
earlier, stone and stucco are functionally
similar, especially their waterproofing
characteristics. In fact, Eldorado Stone,
a synthetic stone manufacturer, even states
on its Web site, “Eldorado Stone requires
the same flashing and waterproofing as
stucco. (This includes the use of a weep
screed.)” Also, Dennis McCoy states in a
December 2004 article in the Journal of
Light Construction, “I’ve been finding more
and more cases of
leaking and rot behind
another material
that is very similar
to stucco: cementitious,
manufacturedstone
veneer.”
These authors
absolutely agree. As
mentioned earlier,
the waterproofing requirements
for synthetic
stone veneer
should be equal to or
better than traditional
stucco because the
likelihood of water reaching the weather
barrier is significantly higher, especially
with “dry stack” stone applications.
Trim accessories include expansion
joints, control joints, casing beads, and
weep screeds (casing beads with weeps).
They are typically manufactured of galvanized
steel or vinyl. The following text separates
the trim accessories and then provides
recommendations for each.
Expansion Joints
Expansion joints are typically required
at floor lines and at changes in substrates.
For example, if the OSB sheathing terminates
at a foundation ledge but the stone
continues, install an expansion joint there.
Expansion joints should still be installed at
floor lines. Wood shrinks due to the climatic
interaction of the original moisture content
– either drying or wetting to the climatic
elements – and the sheathing moves
under structural loads. These loads may
include inward or outward deflections
between “height over 240” to “height over
480.” [In a 10-foot section (or 120 inches),
the wall may deflect between 1/4 and 1/2
inch.] A gable wall attached to a non-gable
wall will have differential deflections located
at the stiff points versus the non-stiff
points. Foundations on soils with variable
properties of expansion or contraction may
result in differential movement. When in
doubt, consult the architect and engineer
on the areas that are most susceptible to
the substructure’s moving and affecting the
product.
Control Joints
Control joints are typically used to “control”
the cracking within the stucco itself. If
control joints are not installed, the stucco
will create them. Stone is not different, as it
incorporates a monolithic cementitious
scratch coat. Some accessories may not
match the surrounding façade perfectly,
but they would look better than missing
stones or cracked grout. Joints can be
installed in the scratch coat and the stones
affixed over them with a side unbonded
(limited to length of bonding). This method
of concealing the joint should be designed
by the engineer or architect.
Casing Beads
Use casing beads around windows,
doors, and any other straight terminations
Figure 3: Penetration integrated into
drainage plane.
Figure 4: Trim accessory used at window jamb. Detail 2
16 • I N T E R FA C E A U G U S T 2007
in the stone veneer. Utilizing casing beads
at terminations provides many benefits:
• Sealant joint widths are set to a uniform
dimension, allowing sealant
trades to apply standard backer rod
sizes and standard work procedures
at the sealant face.
• The sealant joint substrate is a nice,
uniform surface. This helps the
client maintain the sealant in the
future.
• Stone and grout are isolated from
dissimilar materials. We all know
about coefficients of thermal expansion
– materials expand and contract
at different rates. It is unfortunately
common practice to use grout
as a sealant around window and
doorframes. When the windowframe
expands, it exerts a force on the surrounding
grout and usually the
grout will crack, which allows more
water to reach the weather barrier
and travel to the corners of windowsills.
So instead of butting different
materials directly against each
other, let them expand.
Do not use grout as sealant. By installing
casing beads, dissimilar materials
are separated and sealant can be used to
prevent water from reaching the weather
barrier.
Weep Screeds
A weep screed is a casing bead with
weep holes. In stucco applications, weep
screeds are installed at grade and other
horizontal interruptions where drainage of
the system is desired. There is discussion
that the weep holes are for the installation
of the lathe; however, during water entry
and exit, the holes function quite well to
provide a path for water exit. Sloped screeds
do not require weep holes. While using
weep screeds with stone is a good idea, they
may not be necessary. Consider using
heavy-gauge galvanized flashing at horizontal
interruptions, such as grade and paved
surfaces. The key is to provide drainage at
the interruptions.
At-Grade and Paved Surface
Terminations
Why do building codes require stucco to
terminate a minimum 4 to 6 inches from
finished grade and 1 to 2 inches from concrete
flatwork? This is to prevent water
absorption from the grade areas, allow
some drip protection, provide for protection
from insects, and prevent
landscape materials
from contacting the
veneers. Also, by separating
the stucco from
paved surfaces, problems
with differential
movement between the
flatwork and the stucco
can be avoided. Stone is
no different. Many
manufacturers require
at least a 4-inch clearance
to finished grade.
That 4 inches assumes
that the material has
spanned over the foundation
wall to sill line
interface. This overlap
of product is good for
the minimization of air
loss in the tightening of
the building and provides
an aesthetic
band. It also provides
for a system that drains away from the
foundation rather than onto the horizontal
edge of the top of the foundation.
At-Grade Terminations
There are three important things to
remember for grade terminations:
A U G U S T 2007 I N T E R FA C E • 1 7
Detail 3
1. Extend past the plate a minimum of
2 inches.
2. Withhold the stone a minimum of 4
inches from finished grade.
3. Allow the system to drain.
The provided details illustrate two
options for stone terminations at grade.
Both options involve waterproofing and protecting
the interface between the plate and
foundation. Utilizing a strip of SAMB with a
galvanized protection flashing works great
in this application. The first option utilizes
an angle to act as a shelf with weepage provided
at 24-inch centers. Too often, the bottom
stone is susceptible to disbonding from
either snow buildup or water flowing down
the system and a lack of drainage at the
base. The angle will help support this last
stone to better avoid disbonding problems.
Plus, consider the differential movement
between the plate and sheathing termination
and foundation.
The second option involves utilizing a
heavier gauge flashing, 20 gauge vs. 24
gauge, attached only to the plate to limit
problems associated with the differential
movement. Both options require weepage or
a method of drainage to be provided. Weeps
should be provided at tight spacing because
the system is moisture-managed, not a
drainage-plane system that would typically
require a spacing between 24-inch and 32-
inch centers.
Paved Surface Termination
This is the trickiest area to flash and
seal correctly because the paved surfaces,
such as concrete patios, sometimes are
poured incorrectly directly against the top
of the foundation wall. Prior to pouring the
concrete, apply a strip of SAMB with a protective
galvanized
flashing over the
plate/sheathingt
o – f o u n d a t i o n
interface. Then, if
a slab-on-grade
surface is recommended
per the
soils report, a minimum
of 1-inch
clearance must be
provided between
the stone termination
and concrete
to account for possible differential movement
such as frost heave. If a structural
slab is called for, then the differential movement
is minimal and thus less clearance to
the system can be provided as long as the
water that is in the system can get out onto
the concrete surfaces. Weepage should be
provided for both options and the paved
surface should be sloped away from the
structure to avoid ponding water against
the interface.
Lath
The lath is the substrate to which the
stones are adhered. Two general options
exist for the lath behind the stone: 1) 2.5-lb,
diamond-mesh, expanded metal lath; or 2)
18-gauge, woven-wire mesh. Both options
must be galvanized. Greater adhesion capability
is seen with the diamond mesh, but it
must be ensured that the cups are pointed
upward. One small mistake such as that
can equal a large callback due to disbonded
stones.
Whichever lath is chosen for installation,
it should be fastened at 6-inch centers
through the studs, penetrating a minimum
of 1 inch into the studs. The stud locations
can be marked on the foundation wall prior
to the installation of the building paper to
aid the installers in hitting the studs. This
allows the lath to move independently of the
sheathing (remember the one-eighth-inch
joints between sheathing panels). Finally,
be sure to overlap the ends of the lath.
Detail 4 Detail 5
DO NOT MOVE FORWARD UNTIL IT
IS ABSOLUTELY CERTAIN THAT THE
BUILDING IS WEATHERPROOF
WITHOUT ANY WALL CLADDING.
18 • I N T E R FA C E A U G U S T 2007
Stone Application
The first decision during actual stone
application is whether or not a scratch coat
should be installed over the lath. While
some stone manufacturers require a
scratch coat, others are somewhat vague
with their requirements. So what should be
done if the manufacturer’s instructions are
vague? In this case, one should apply a
scratch coat over the lath. The scratch coat
will completely cover the weather barrier
and will provide a solid substrate for subsequent
stone application. Some manufacturers
require that the stone be installed before
the scratch coat has fully cured, and these
authors agree. This may limit the amount of
scratch coat that can be installed at one
time, but the increased adhesion may be
worth the potential increase in application
time.
The second decision involves application
techniques due to weather conditions
at the time of installation. If the synthetic
stone veneer is to be applied during either
very hot or very cold temperatures, special
measures should be taken to ensure the
stones are securely bonded.
Hot Weather
During hot weather (generally above
90˚F), mortar will surface cure more quickly,
which can cause it to become brittle.
Also, the stone itself may be very dry and,
therefore, want to absorb the water in the
mortar, again negatively affecting adhesion.
So if the stones will be applied during hot
conditions, dampen both the scratch coat
and stone prior to application. By wetting
both surfaces to receive mortar, the mortar
can cure at a more natural rate, and accelerated
dehydration will be avoided.
Cold Weather
Mortar contains water. Water freezes at
32˚F. Mortar can take 14 days to fully cure.
Do not apply stone if the temperature will
fall below 32˚F during the curing period. If
this cannot be avoided, tent and heat the
area. While this will most likely increase the
initial cost of application, it will probably
save money down the road due to fewer callbacks
and increased customer satisfaction.
Application Methods
There are two basic installation methods
for stone application, and both relate to
the joint size between stones.
Traditional Grouted Joint Method
This method of stone application leaves
approximate 1/2-in to 3/4-in joints
between the stones that are later grouted.
This more traditional method prevents a
greater amount of water from reaching the
scratch coat or lath and, subsequently, the
stone’s point of adhesion. It is preferable to
start from the top and move downward to
avoid mortar from spilling onto alreadyapplied
stone courses.
Dry Stack Method
The dry stack method involves stacking
and butting the stones from the ground up
directly against one another. Therefore,
there are no joints to grout between the
stones.
Exercise caution if the dry-stack
method is to be used in cold climates. Many
disbonding problems are seen with drystack
stone in cold climates, such as the
Rocky Mountain region here in Colorado.
Because the joints between stones are not
grouted, rain and snow can easily travel to
the scratch coat (point of adhesion) and the
weather barrier. Also, because every stone
is slightly different in shape, some may protrude
past others and act as a gutter that
captures water and channels it toward the
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A U G U S T 2007 I N T E R FA C E • 1 9
scratch coat and
weather barrier.
Therefore, water
that travels against
the adhesion point
can cause disbonding
through freezethaw
cycles. The
same problem occurs
near grade
where snow can
build up against
the dry-stack stone.
The worst scenario we have seen
occurred when the dry stack method was
chosen in a cold climate and no scratch
coat was applied. Plus, it appeared the
installer “value engineered” the amount of
stone and left joints between them.
Needless to say, disbonding is a major ongoing
issue, among many others.
If synthetic stone veneer is to be applied
in cold climates, if at all possible, avoid the
dry stack method. If the dry stack method is
used, at least use a scratch coat to avoid
copying this “worst case scenario.”
Specialty Stones
Most manufacturers create stones
specifically for use at locations such as windowsills,
water tables, and interior and
exterior corners. The windowsill and water
table stones are typically
manufactured
with slope to shed
rain and snow off
the surface. Regardless,
if specialty
stones are being
used at windowsills
and water tables,
the stone course
should be sloped a
minimum of 15
degrees to shed
water away from the joint above. This is
especially important at windowsills where
the weather barrier behind the stone can be
susceptible to problems.
The same worst-case scenario also
involved an absence of flashing membranes
around the window, the building paper was
back-lapped at the sill, and the stones at
the sills were dead-level or even negatively
sloped. When snow collected on the sill, it
melted inward and traveled behind the
building paper. Not surprisingly, the gypsum
sheathing under windows deteriorated,
and mold growth was occurring.
Rain has the same effect. If the water on
the exterior face can be managed, then the
proper interior side of the veneer will have a
fighting chance. Remember that this system
is a moisture-managed system, not a drain
plane system, and large amounts of water
cannot be handled by the paper layers without
eventual deterioration.
Dissimilar Façades and Water Tables
As stated earlier, most façades do not
consist entirely of one type of veneer. The
horizontal interface between two façades is
sometimes referred to as a “water table.” It
is common to use stucco or siding above
stone. It is also common to find improperly
installed weatherproofing at the water table
interface. The lack of coordination between
trades, which corresponds to a lack of the
prime contractor’s oversight on the job site,
is the primary cause of problems at this
interface. Determination of the responsible
trade for installing the water table flashing
must be spelled out in the contracts. A good
deal of post-construction fingerpointing
occurs when this area fails. Define it up
front and avoid this issue.
Here are two helpful hints to avoid problems
at the water table interface:
1. The drainage plane and weather
barrier should be continuous behind
the interface.
2. Don’t let water get behind the lower
façade. Shed the water onto the surface
of the lower façade. This can be
accomplished by sloping the stone
and utilizing a sheet-metal flashing
Detail 6 Detail 7
20 • I N T E R FA C E A U G U S T 2007
Figure 5: Worst-case scenario. Note missing
scratch coat between stones.
that extends from behind the
stucco over the sloped stone
piece. The flashing must be
sloped as well.
Embedded Ledger Boards
It is common to see the ledger board
embedded in the field of the stone.
Unfortunately, this condition promotes
premature deterioration of the ledger
board due to a lack of flashing and
waterproofing. Mortar absorbs water and
acts as a sponge. When the ledger board
is constantly in direct contact with a wet
sponge, it will rot out much faster.
An easy way to avoid this problem is to
isolate the embedded ledger board from the
mortar and flashing over the top to shed
water to a surface below. The top edge of the
ledger board should be beveled and the
flashing should be positively sloped to avoid
ponding water. Below the ledger board, it is
best to install a flashing that extends from
behind the ledger board over the stone
below. This way, when the ledger board is
replaced, it will not damage the surrounding
stone. Another option would be to seal
the interface between the bottom of the
ledger and the top of the stone.
Roofs
The kickout flashing may be the most
important piece of flashing on the building
that has to transition between surface products.
After the windowsills, the second most
common error is when a kickout (or diverter)
flashing at rake wall terminations is
missing. Without the kicker flashing, the
water is channeled into the stone veneer,
which not only increases the likelihood for
debonded stones, but also ultimately allows
excess water into the moisture-managed
system. Further, it is common to cut the
building paper around the rake termination,
so not only is the water directed into
the stone veneer, but also behind the
weather barrier. Make sure kicker flashings
are installed and make sure the weather
barrier is continuous behind the flashing to
catch any incidental water.
Maintain clearances above the roofline
similar to the clearance above the concrete
and asphalt at the first-floor level. Installing
a trim accessory such as a weep screed can
be useful for setting the stone clearance
height prior to the actual stone application.
Protective Coatings
Some homeowners want to install a
clear waterproof coating over the stone
veneer, wishing to protect the stone from
weathering. If this coating is planned for the
home, it must be a vapor-permeable coating,
such as a silane or siloxane. If an
impermeable coating is installed, the natural
drying ability to the exterior is reduced.
Combined with walls full of insulation and
an interior vapor retarder, deficiencies that
allow water behind the stone result in a wall
that cannot dry to the interior or exterior.
Moisture-sensitive building materials (i.e.,
wood) will deteriorate even faster. A coating
will not save the system if the underlying
materials have been improperly installed.
Summary
Stone is functionally similar to stucco;
even stone manufacturers disclose this.
Stone requires equal or better weatherproofing
details than stucco, especially
when dry-stacked. If the architect or client
insists on the dry-stack look in a cold climate,
then greater attention to waterproofing
details, application techniques, and
manufacturer requirements must be
adhered to in order to avoid costly callbacks.
It all starts with a proper weather
barrier. This is the most important step in
any façade installation, especially stone.
Synthetic stone veneer is here to stay.
Stone has been used as a building material
since man moved into caves and called
them home. Synthetic stone is a product
that will continue to be utilized in the construction
of buildings. With improved manufacturing
techniques, almost any stone
architectural “look” can be achieved and
appear completely natural. Unfortunately,
waterproofing techniques and the skill of
application have not caught up with the
improved stone manufacturing techniques
and “tighter” construction practices.
References
Acceptance Criteria for Cementitious
Exterior Wall Coatings, ICBO ES
Report AC11.
Brick Industry Association – www.bia.org.
Butt, Thomas K., “Water Resistance and
Vapor Permeance of Weather-
Resistive Barriers,” Journal of ASTM
www.rci-mercury.com
A U G U S T 2007 I N T E R FA C E • 2 1
SYNTHETIC STONE VENEER IS HERE TO STAY…
WITH IMPROVED MANUFACTURING TECHNIQUES,
ALMOST ANY STONE ARCHITECTURAL “LOOK” CAN
BE ACHIEVED AND APPEAR COMPLETELY NATURAL.
International, November/December
2005.
Cast Stone Institute – www.caststone.org.
Cultured Stone, www.culturedstone.com.
Eldorado Stone, www.eldoradostone.com.
Fisette, Paul, “Housewraps, Felt Paper
and Weather Penetration Barriers,”
w w w . u m a s s . e d u / b m a t w t /
publications/articles/housewraps_f
eltpaper_weatherpenetrationbarriers.
html, 2001.
Fisette, Paul, “Leaky Housewraps,”
www.umass.edu/bmatwt/publications/
articles/leaky_housewraps.ht
ml, 2000.
Lstiburek, Joe, “Water Managed Wall
Systems,” Journal of Light
Construction, March 2003,
www.jlconline.com.
McCoy, Denis, “Manufactured-Stone
Nightmares,” Journal of Light
Construction, December 2004,
www.jlconline.com.
Portland Cement Plaster Stucco Resource
Guide, Northwest Wall and
Ceiling Bureau, www.nwcb.org.
Rocky Mountain Masonry Institute –
www.rmmi.org.
Edward L. Fronapfel, PE, is a principal with Professional
Investigative Engineers, Arvada, CO. He has been affiliated
with the following organizations: ICBO (International
Conference of Building Officials), AISC (American Institute of
Steel Construction), NSPE (National Society of Professional
Engineers), active Chapter Mathcounts chairperson, ACI
(American Concrete Institute), APA (The Engineered Wood
Association), AFPM, (American Forest Products Association),
CSAFPM (Colorado State Association of Flood Plain Managers),
BOCA (Building Officials Council of America), AITC (American Institute of Timber
Construction), I-Eng-A (Investigative Engineers Association), Colorado Chapter ICC
(International Code Council), CAI (Community Association Institute), Colorado Chapter
of Building Officials, CAHB (Colorado Association of Home Builders), NIBS (National
Institute of Building Sciences), RCI, EEBA (Energy Efficient Building Associations), HBA
(Home Builders Association), and SSPC (The Society for Protective Coatings).
Edward L. Fronapfel, PE
22 • I N T E R FA C E A U G U S T 2007
The International Masonry Institute (IMI) is a
strategic alliance between the International Union of
Bricklayers and Allied Craftworkers (BAC) and their
signatory contractors to promote quality masonry construction.
IMI offers free technical assistance to the
design and construction communities, as well as
training for craftworkers and professional education
for masonry contractors.
IMI’s network of 12 regional centers and the
National Training Center (currently being constructed
in Bowie, MD) offer training at all career levels (from
apprentice to supervisor) in all the masonry crafts:
brick/block, tile, terrazzo, marble, stone, restoration,
plaster and cement, plus new products and systems.
A masonry detailing series may be found at
www.imiweb.org. The interactive details give designers
easy-to-use, practical solutions for their masonry projects,
with drawings, images, narratives, animations,
and more. Learn more at www.imiweb.org or
www.bacweb.org or call 1-800-IMI-0988 or 1-888-
880-8222.
INTERNATIONAL MASONRY INSTITUTE
Brian D. Erickson, EIT, is a forensic specialist with
Professional Investigative Engineers. He holds a B.S. in
industrial engineering and is a Master’s candidate in civil
engineering at the University of Colorado. He has widespread
building envelope, roofing, and waterproofing experience.
Brian is also involved with rehabilitation document preparation
and project management, in addition to publishing articles
and speaking to the construction industry regarding
building science and moisture control.
Brian D. Erickson, EIT