Communication between designer and the contractor is crucial to achieve both conceptual
and actual level of quality.
Quality of work pertains to how to Spec masonry to ensure GC handles it correctly.
Presenter's Notes
All manufactured masonry units, including concrete block, clay brick and calcium
silicate masonry, are inherently absorptive.
Masonry units will physically suck the mortar into their pores creating a strong
mechanical bond necessary for a durable wall.
Continuous exposure to moisture-laden soil at grade leads to rising damp.
De-icing salts rapidly deteriorate manufactured masonry units. As the salts enter the
pores of the masonry and crystallize they expand and create voids. As this process
repeats the voids get bigger.
Presenter's Notes
The easiest way is to simply avoid contact with water at grade by raising the veneer up
150 mm from finished grade.
150 mm buffer is a Canadian code requirement. 6” requirement is in US code but not
enforced as strongly.
Concrete = hydrophilic material (loves to absorb moisture); wicks moisture up into
veneer through capillary action.
Cavity wall design: “cavity”, or air space, between the veneer and the substrate.
Cavity should be at least 25 mm wide; 38 mm or 50 mm is preferable but not always
possible.
Prevents airborne moisture from jumping from one material to another; very common
method of infiltration.
Flashing membranes are typically a rubber material adhered to the substrate or
sheathing behind veneer that direct moisture flow in the cavity down to its base and out
the weep holes, protecting the sheathing and substrate materials behind.
Weep holes are placed in head joints of veneer units to provide the means for moisture
to escape the cavity.
Therefore, flexible flashing membrane has two important functions:
acts as a surface that directs moisture out of the wall system from above.
acts as a capillary break (hydrophobic material), preventing moisture from wicking up
into the wall system from below.
Presenter's Notes
There are many alternatives to addressing masonry at-grade concerns.
Install a dolomitic limestone starter course at the base of the masonry veneer.
Dolomitic limestone is a Class III limestone and has a greater density and lower
absorption than calcium silicate and as such is ideally suited to resist the conditions
at grade.
Especially de-icing compounds which are much more of a threat than simple moisture in
northern climates.
Presenter's Notes
Install a moisture-impervious protection board on the face of the masonry veneer.
The protection board will protect the masonry veneer from saturation by segregating it
from the moist soil.
This method is virtually invisible.
Typically more viable with smooth-faced units below grade as opposed to rocked.
Presenter's Notes
No drip cut causes moisture to cling to the underside of the cap overhang. That moisture
can be blown back on to the masonry below causing the effect we see here.
Lime bloom is seen here because moisture has infiltrated through the cap (due to multi
mortar joints), saturated the masonry and its mortar joints. The lime constituent in the
mortar mix is brought forth by the migrating moisture.
Inadequate cap flashing allows precipitation to infiltrate the wall assembly and
saturate the masonry veneer.
This is a combination of incomplete design and poor construction practices.
Wind driven rain is blown up under the cap flashing. The moisture is then absorbed by
the mortar blockage within the cavity. The moisture slowly migrates from the cavity to
the outer face of the veneer.
3-4 days after the rainfall the units can be seen as wet and stained.
Presenter's Notes
The top of a building is very windy, especially in taller structures. If the cap slopes
downward toward the face of the building, the wind will blow the water back onto the
masonry, resulting in a stained and saturated veneer wall.
Sloping the cap towards the non-visible face also carries any dirt away from the façade
as well.
It is unreasonable to expect every cap to be a solid component such as a quarried stone
or metal cap flashing. For traditional unit masonry caps, which are not ideal, make sure
to seal the joints between individual pieces. Each joint represents a potential source
for moisture penetration of the wall assembly, so ensuring they are all sealed will help
offset the intrusion of moisture in a masonry cap’s many joints.
Presenter's Notes
This is a good time to note that in addition to properly detailing areas such as sealed
joints in stone caps, proper maintenance throughout the life of the building is crucial
for the long-term durability and aesthetics.
For example, typically sealants have a lifespan of about 25 years, but should be checked
regularly to ensure there are no potential weak spots where moisture can infiltrate.
Presenter's Notes
That being said, some moisture WILL penetrate the cap and get inside the parapet
assembly. To help battle this, continuous flashing is installed directly below the cap
to help drain moisture away. The flashing should extend over the wall’s cavity.
This flashing should not be a flexible membrane material, as it could sag when over the
cavity and lead to overlapping pieces of membrane providing spots for water to pool at
or seep into the cavity.
To prevent moisture from staining the masonry directly below the cap, overhangs and drip
cuts are used to terminate the flow of water from the cap before it can settle on the
face of the veneer.
Presenter's Notes
When using a metal flashing cap, many of the same principles apply.
The cap is sloped towards non-visible face for the same reasons as with a stone cap.
Flashing is installed under the cap for the same reasons.
A drip edge serves the same function as an overhang and drip cut in a stone cap. The
idea is to keep moisture away from the face of the veneer below.
Sealing the underside of the flashing prevents wind-driven moisture infiltration, and
also the intrusion of insects into the wall cavity.
SMACNA = Sheet Metal and Air Conditioning Contractors National Association
SMACNA has recommendations on how the crimp and bend metal to make the joints water
resistant.
Presenter's Notes
Proper detailing of a window sill is very similar to that of a parapet cap.
The sill is provided with an overhang and drip cut to again prevent the flow of moisture
to the face of the veneer below.
Presenter's Notes
Since a large volume of moisture will be accumulating at the base of openings, all sills
should have flashing membranes installed to guide the moisture out of the wall assembly.
End dams are formed by turning up the flashing at the termination of the opening. They
serve to ensure that no moisture will get behind the masonry veneer below the sill.
Provide weep vents either between the sill and end dam, or simply in the head joints of
the sill units.
Presenter's Notes
Metal sills incorporate the same detailing as metal parapet caps, and window sills as
well.
Presenter's Notes
The “2/3” rule is an easy-to-remember rule for whenever using a shelf angle.
Typically the joint below is 3/8” but it must be at least ¼”.
Base of cavity detailing applies at the window or door head.
Presenter's Notes
Yeo Hall at the Royal Military College in Kingston, ON.
Windows have slopes and overhangs. Note the lack of staining or efflorescence.
The left portion of the building is over 100 years old. That means even a century ago
designers understood the effects of water and designed way to prevent them.
The right portion of the building is much newer and adopts the same conventions.
Slopes and overhangs are present but they have also included new things such as
under-sill flashing and drip cuts.
Presenter's Notes
Base of cavity detailing above shelf angle.
Since there is masonry above AND below the shelf angle, it is absolutely critical that
the deflection space below the angle is a soft joint.
Horizontal movement joint below the angle will accommodate the shrinking of the concrete
block back ups, the deformation of steel structures, the deflection of the shelf angle,
and the expansion of the masonry veneer.
More discussion on that when we get into the movement joint portion of the
presentation.
Presenter's Notes
Here you can see strong horizontal lines where shelf angles are.
Can use lipped units to hide shelf angle and make joint appear as just another mortar
joint.
Presenter's Notes
Just discussed managing moisture; now focus on differential movement and how it affects
our design.
Does everybody here understand what is meant by “differential movement” ?
All building materials are in a constant state of motion, be it from thermal changes,
absorbing moisture, or dead/live loads imposed and creating stresses in the materials.
If we simply construct a building while disregarding the materials’ desire to move in
all these different directions, we will see cracking related to these differential
movements. Restraining the movement of the materials leads to stresses.
Presenter's Notes
We are going to focus primarily on the differential movement characteristics of
manufactured masonry materials.
Because of these different net movements, manufactured masonry materials behave
differently when combined in a wall. We will touch on that shortly.
Presenter's Notes
Why do we put anything in the joint at all? Why not just leave it open to allow maximum
movement of materials?
We just spent the past half hour talking about how we’re trying to minimize water
infiltration into the building. How will we be able to limit the entry of water if we
have gaping holes in the wall?
The joint filler and backer rod/sealant allow for movement of the materials while
retaining the water resistance of the wall we require.
Sealant works great in tension/compression but not shear. Three-point adhesion subjects
sealant to shear and T/C.
Size of joint may vary but 3/8” should suffice for most applications. Depth of sealant
should be 3/16” in that case.
Presenter's Notes
Marble in sliding door analogy.
Presenter's Notes
Changes in wall direction (i.e. corners) are one of the biggest areas of concern for
differential movement.
Similarly to corners, window/door openings will create weak areas for masonry.
Change in wall height is a problem because the masonry “above” will want to move towards
the corner while the masonry below won’t. Place a horizontal joint so the top mass can
move freely.
At columns/pilasters, the materials will want to be moving in several directions.
Movement joints at inside corners are ideal here.
For clay brick and calcium silicate masonry, if there are no other conditions that call
for a joint, one should be placed at no more than 6 m lengths.
Whenever two different materials meet there should be a movement joint to accommodate
the materials’ different properties of expansion. For example, masonry will expand at a
much different rate than aluminum.
Below shelf angles there should always be movement joints to account for deflection of
the angle.
Presenter's Notes
Movement is an additive effect.
As the units expand they will want to move towards the weakest part of the building.
If not accommodated, stresses at the corners will tend to push the walls away from one
another. Masonry will want to expand outward from the centerline of the wall toward the
weakest point, typically at corners.
L1 + L2 ≤ typical spacing between expansion joints (6 m - 7.6 m).
Either dimension should not exceed 3 m (10 feet).
It is preferable if they are closer to 1.2 m (4 feet) to err on the side of caution.
Presenter's Notes
Masonry will want to move towards the weakest plane it can find.
When placing vertical movement joints at openings, the masonry adjacent to the opening
will want to move toward it.
The opening itself has a lintel atop it to support any masonry above. The movement of
the masonry below will create friction between the masonry and the steel lintel.
For this reason, a slip joint around the lintel is used to avoid the common issue of
cracking around the corners of the opening.
Typically this is done by placing a layer of flexible flashing between the lintel and
masonry to allow the masonry to move independently of the lintel.
Presenter's Notes
Movement joint design and placement can affect the aesthetics of the veneer.
Several considerations can minimize their impact.
Presenter's Notes
While there are no material-specific requirements for the use of joint reinforcement,
design factors such as quirk miters or stack bonded configurations may call for
additional reinforcement of joints.
Presenter's Notes
In addition to the 6m – 7.6m spacing, additional control joints must be placed every
1.5x the height of the wall.
i.e. a 10’ high CMU wall would need a control joint every 15’.
Horizontal joint reinforcement is because concrete is very strong in tension/compression
but weak in shear. As the units cure the shear forces will cause cracking. The
horizontal reinforcement is the opposite of concrete and is good in shear so it carries
those shear forces to avoid cracking.
Presenter's Notes
There is no need for horizontal joint reinforcement since we are repointing the joints
with sealant.
Presenter's Notes
We do not want units to become wet from soil.
Do not use de-icing compounds to melt snow or ice from masonry units.
Storing the units properly eliminates the need to melt snow or ice from masonry.
Presenter's Notes
Place polyethylene or other plastic film between wood and masonry units if stored for
extended periods of time.
Presenter's Notes
The primary concern when working in hot weather is the curing of the water in the cement
of the mortar.
Additionally, other mortar materials (lime) may ‘flash set’ and cause cracking within
1-2 days of construction.
These are some industry guidelines that should be in the specifications for the mason to
follow.
One way to pre-dampen units is to run a hose over skids of units for up to 30 minutes.
This can be done on the previous day, and should be done no less than 5 hours prior to
the units being used to ensure the units are reasonably wetted but surface dry.
In addition to working in the shade, masons should try to work early in the morning as
opposed to the hot afternoon.
Presenter's Notes
Similar to hot weather construction, cold weather brings with it considerations for
keeping the mortar at an adequate temperature.
If the water in the mortar is at too low of a temperature it may freeze before curing.
The use of mortar admixtures such as set accelerators is not recommended.
Provide wind-proof enclosure and supplementary heat as required to maintain air
temperature above freezing during installation and for 24 hours thereafter.
Follow the typical storage recommendations as well.
Presenter's Notes
Masonry ties can be used to connect two wall wythes together in a composite wall. We are
more concerned with their second use: connecting a masonry veneer wythe to the
structural backup.
Tie must be stiff to resist lateral wind loads.
Presenter's Notes
Unit Ties are typically made from a single component, either sheet metal or wire and
they are available in various configurations, including wire ties, Z-wire ties, and
corrugated straps.
Presenter's Notes
Joint Reinforcement is designed to produce a lightweight yet strong method of bonding
two or more wythes of coursed masonry together.
Presenter's Notes
A design professional, in consultation with the tie system manufacturer, should
carefully consider all of these factors in order to properly select the appropriate
type, quantity and strength of tie required.
Presenter's Notes
Type N cement-lime mortar mixed to a 1:1:6 Proportion Method ratio is preferable to Type
S for masonry veneers for its flexibility and workability.
Type S lime is “Special” and gives better water retention properties to the plastic
mortar.
Presenter's Notes
Thoroughly mix mortar ingredients in proper quantities needed for immediate use.
Measure quantities of materials by weight or volume.
Use full bags of cement and lime.
Calibrate shovels of sand to a gauge box with each change in shift or mixing operator.
Use mortar within 2-1/2 hours after initial mixing. Mortar that has stiffened may be
re-tempered up until such time expires.
Presenter's Notes
Minimize the amount of mortar squeezing into the cavity.
Presenter's Notes
‘Thumbprint hard’ is when you can press your thumb into the mortar and leave a finger
print, but the mortar won’t stick to your finger.
Regardless of the joint profile, to achieve a weather-resistant joint, tool the joints
to a smooth, tightly compressed surface.
Presenter's Notes
When site cutting units, always pre-wet them. Doing so will saturate the units so that
any dust from cutting will not enter the pores.
Presenter's Notes
When site cutting units, always pre-wet them. Doing so will saturate the units so that
any dust from cutting will not enter the pores.
Presenter's Notes
Spray cleaners should be MAX. 40-50 psi.
Presenter's Notes
Spray cleaners should be MAX. 40-50 psi.
Presenter's Notes
Maintaining good quality of work and using time-tested masonry materials and methods
will ensure a long-lasting masonry wall.
Consider the following areas when constructing walls with masonry veneer.
Thank you for your interest in this Continuing Education Course.
This concludes the American Institute of Architects Continuing Education Systems Program.
Click below to download the Proper Masonry Detailing Online Exam
