“The Basics ofBrickwork Details”

Glen-Gery’s Brickwork Techniques Seminar Series:

1

“The Basics ofBrickwork Details”CAUTION: This document is intended for use in conjunction with the Seminar Presentation:“BASICS OF BRICKWORK DETAILS.” Understanding many of the concepts and details presented in this document requiresfurther explanation which is provided in the seminar. Also, the documents listed below provide additionalinformation that should be understood before attempting to apply the information in this document to specific applications.

Reference List

1. Seminar: Basics of Brickwork Details

2. Brick Industry Association Technical Notes on Brick Construction:(www.bia.org)

#1 – All-Weather Construction#3 – Overview of Building Code Requirements for Masonry Structures#7 – Water Penetration Resistance – Design and Detailing#7A – Water Penetration Resistance – Materials#7B – Water Penetration Resistance – Construction and Workmanship#8 – Mortars for Brick Masonry#8B – Mortar for Brick Masonry – Selection and Controls#18 – Movement – Volume Changes and Effect of Movement, Part I#18A – Movement – Design and Detailing of Movement Joints, Part II#20 – Cleaning Brick Masonry#21C – Brick Masonry Cavity Walls – Detailing#23 – Efflorescence, Causes and Mechanisms, Part I of II#23A – Efflorescence, Prevention and Control, Part II of II#28 – Anchored Brick Veneer – Wood Frame Construction#28B – Brick Veneer/Steel Stud Walls#36 – Brick Masonry Details – Sills and Soffits#36A – Brick Masonry Details – Caps and Copings, Corbels and Racking

3. National Lime Association (www.lime.org)Lime-Based Mortars Create Watertight Walls

4. The Masonry Society (www.masonrysociety.org)TMS 402 Building Code Requirements for Masonry Structures

5. Glen-Gery Corporation (www.glengerybrick.com)Brickwork Design Profile 4t1, Cleaning New BrickworkBrickwork Design Profile 4t2, Masonry Construction RecommendationsBrickwork Design Profile 4p7,Glen-Gery Glazed Brick

6. ASTM, InternationalC 270, Standard Specification for Mortar for Unit Masonry

This publication is intended solely for use by professional personnel who are competent to evaluate thesignificance and limitations of the information provided herein, and who will accept total responsibility forthe application of this information. To the extent permitted by law, Glen-Gery Corporation disclaims anyand all responsibility for the accuracy and the application of the information contained in this publication.

Glen-Gery’s Brickwork Techniques Seminar Series:

2

PART ONE: Movement

There are four basic causes ofmovement in masonry materials:

1. CHANGES IN TEMPERATURE

2. CHANGES IN MOISTURECONTENT

3. FREEZING EXPANSION

4. DEFLECTION:Elastic and Plastic (creep)

THERMAL MOVEMENTSEvery material expands or contracts

as the temperature of the materialchanges, typically expanding as itstemperature increases and contractingas its temperature decreases. Differentmaterials expand and contract atdifferent rates when they undergosimilar changes in their temperatures(Figure 1). When discussing wall sys-tems, changes in the sizes of materialsare of particular concern when theyoccur in the plane of the wall. Whendiscussing wall systems, differing ratesand directions of expansion or contrac-tion of adjacent building materials arealso of concern.

Brick veneer can expand andcontract approximately 7/16" per100 feet per 100º F temperature swing(kt = 0.000004 inch per inch per ºF).When calculating the expansion orcontraction of a brick veneer using thisfactor, it is important to remember theeffects of the sun on materials. Theenergy from the sun’s rays raises thetemperature of a material well abovethe air temperature: On a day whenthe air temperature is 32º F, the energy from the sun can raise a wall’stemperature to above 100º F. Thetemperature of the wall is what isimportant. The sun can raise the tem-perature of dark materials to 160º F ormore and lighter-colored materials to120º F and these values should beused in design. Because a wall facingnorth or nearly so receives little or nosun in the Northern Hemisphere, thetemperature of such a wall rarelyexceeds the air temperature.

We often forget that buildings arerarely constructed at either 140º F or0º F and that the amount of movement

is not determined by the differencebetween the maximum temperatureand the minimum temperature. In thecase of expansion, the amount ofmovement is actually determined bythe difference between the maximumtemperature and the temperature ofthe wall when it was built. Similarly, inthe case of contraction, the amountof movement is determined by thedifference between the temperatureat which the wall was built and theminimum temperature.

MOISTURE MOVEMENTSMoisture affects all porous masonry

materials, including brick, mortar, con-crete masonry units, and stone, but invery different ways. These effects mustbe considered when a combination ofthese materials is used, such as whenbrick rests on a concrete foundation,brick veneer units are used with blockback up, and when brick and architec-tural concrete products are used in the same wythe – bands of precastconcrete or architectural concreteblock in a brick veneer.

After their initial mixing or casting,mortar, poured-in-place concrete, and concrete masonry units shrink asthe curing of the Portland cement proceeds. This is an unavoidable consequence of the curing of concreteproducts and is accommodated indesign.

Mortar, concrete, and concretemasonry units also exhibit relativelymajor shrinkage movements as theydry during and immediately followingconstruction. If, after initial drying,materials containing Portland cementconcrete become wet, they willexpand. As they dry again, they willshrink.

Brick masonry, on the other hand,does not shrink as it cures and dries inthe wall. Brick masonry has an initialmoisture expansion that is notreversible, just as is the shrinkage ofconcrete products as they cure is notreversible. As with concrete products,this change in size is accommodatedin design.This expansion occurs ascompletely dry brick (typically fired inexcess of 1800º F) are exposed to themoisture (humidity) in the air outsidethe kiln. Some brick expand more thanothers during this period. Manyexpand so little that the expansion isinsignificant. Most moisture expansionoccurs during the first two monthsafter leaving the kiln. For most designpurposes, a factor of moisture expan-sion of ke = 0.0005 inch per inch maybe used. As the moisture expansion ofbrickwork is in the opposite directionof the drying shrinkage of concrete orCMU, the differential movement maybe significant. Composite masonrysometimes fails to perform properlybecause of these opposing move-ments. When composite systems are

Brick Masonry

Dense CMU

Structural Concrete

Structural Steel

Aluminum

Lightweight CMU

7/16"(11 mm)

COEFFICIENT0.000001 in/in/ºf

MOVEMENTin/100 ft/100ºf

1/2"(13 mm)

5/8"(16 mm)

3/4"(19 mm)

13/14"(20 mm)

1-9/16"(39 mm)

THERMAL MOVEMENT OF BUILDING MATERIALS

3.6

4.3

5.2

6.0

6.7

12.8

Figure 1

Figure 1

3

used, the placement of movementjoints in the brick and control joints inthe concrete or CMU must receiveadditional attention.

Joint reinforcement is typicallyplaced in the bed joints of concretemasonry to help control shrinkagecracking. If joint reinforcement andcontrol joints are placed properly,cracking should be limited to the con-trol joints. This reinforcement can beeither the “truss’’ type or the “ladder’’type. Truss-type 3-wire reinforcement,which has the third wire in the brickmasonry bed joints, should not beused unless the wall system isdesigned as a composite wall with agrouted collar joint. In cavity or veneerwall systems, truss-type reinforcementcan transfer forces to the brick wythe, forces which may cause damage to the mortar joints or loss ofembedment of the wire. Note thatANY three-wire system may cause difficulties when laying the two wythesif one wythe is completed before theother; therefore, the “eye and pintle’’system is preferred (Figure 2). If brickis laid in stack bond, horizontal jointreinforcing must be placed in the bedjoints of the brick wythe to inhibitcracking of the continuous (vertical)head joints.

FREEZING EXPANSIONFreezing expansion occurs when

clay masonry units saturated withwater are frozen and the temperatureof the frozen, saturated units goesbelow 14º F. The coefficient of freezing expansion is kf = 0.002 inchper inch, but, since proper designdoes not allow masonry to becomesaturated, the coefficient of freezingexpansion is usually not included inthe design equations.

DEFLECTIONThe sum of the elastic deflection

and the plastic deflection of memberssupporting masonry must be limitedto the lesser of 0.30" or L/600.

CALCULATING THE AMOUNTOF MOVEMENT

Actually, we are not really interestedin the amount of movement! Rather,because the widths of movement jointsare usually arbitrarily set, we are inter-ested in determining how far apart themovement joints should be placed.Brick Industry Association TechNote18A addresses movement jointspacing with this equation:S = [w • e] ÷ [ke + k f + k t ∆T ]Where,

S = spacing between adjacentjoints in inches

w = width of the movement joint ininches

e = extensibility or compressibilityof the sealant/filler

ke = coefficient of moisture expan-sion, in./in.

k f = coefficient of freezing expan-sion, in./in. (Usually ignored)

k t = coefficient of thermal expan-sion, in./in./ºF

∆T= change in temperature of thebrickwork,ºF

There are at least two conditionsthat must be checked; the temperaturechange between the construction tem-perature up to maximum wall tempera-ture and the temperature changebetween the construction temperaturedown to minimum wall temperature.

MOVEMENT JOINTSMovement joints in the brickwork

should be placed at regular intervals inthe structure to help prevent large

tensile, compressive, or shear stressesfrom developing. If large stresses arenot generated, cracks cannot occur. Amovement joint is a discontinuity in thestructure – a break in the fabric of thebuilding – that allows movement tooccur and prevents the build-up ofstresses. In most brick veneer structures, the only evidence of a movement joint is a very thin vertical orhorizontal band at the face of the wall.The exposed portion of this band isusually an elastomeric sealant whichprevents rain, snow, debris, and smallplants and animals from filling the move-ment space or entering the structure.

One of the decisions that thedesigner must make is how wide thisband may be without unduly disturbingthe eye. Usually, designers limit thewidths of the joints to 3/8" to 1/2",about the width of the mortar jointssurrounding the movement joint. Thisdecision is a key ingredient in theequation used to calculate the spacingof movement joints. To a degree, widerjoints allow greater spacing betweenjoints and narrower joints require closerspacing of joints.Movement joints morethan 3/4" wide are not recommended.

In most building construction amovement joint must include a sealant,a backer rod, and a compressible fillermaterial. Always use sealants whichare capable of accommodating thecalculated movement without failing.These sealants should comply with therequirements of ASTM C 920. Checkwith your sealant suppliers for theirrecommendations, as some very pop-

Figure 2

VENEER AND CAVITY WALLREINFORCING

Movement Joint

MOVEMENT JOINT

Control Joint

Figure 3

VENEER AND CAVITY WALLREINFORCING

MOVEMENT JOINT

Figure 2 Figure 3

4

ular construction sealants do not bondwell to masonry products. Be sure totake into account all materials to whichthe sealant must bond (i.e., brick, con-crete, window frames, flashings, shelfangles or metal caps) since some mustbe primed before certain sealants areapplied. Sealants generally performbest when the ratio between the widthof the sealant and its depth is about2:1. Beads of sealant applied in a filletor butt configuration have a muchreduced service life.

A backer rod must be present tosupport the sealant during installationand tooling while also providing a bondbreak between the sealant and com-pressible filler. Backer rods may not benecessary if the sealant does not bondto the compressible filler and the fillerprovides adequate support for thesealant. Backer rods are usuallysmooth, closed cell foam ropes thatare larger than the joint and which areforced into place before the sealant isinstalled. Compressible fillers areinstalled to keep mortar or othermaterial from filling the joint. The com-pressible filler may be installed duringconstruction to prevent mortar fromfilling the joint during brick laying andreducing the movement capacity of thejoint. These fillers must have a com-pressibility equal or greater than themaximum compressibility of thesealant, which is generally no greaterthan 50%. Many filler materials areavailable, including premoldedrubber and plastic.

HORIZONTAL MOVEMENTSWhen the cyclical movements

associated with horizontal expansionand contraction have not been consid-ered during design, corners areparticularly susceptible to crackingcaused by tensile and shearingstresses. Figure 4 shows what canhappen when the brick veneer expands– a crack develops at the corner.

Cracks may also develop atwindows, doors, changes in crosssection, or other weak points in themasonry. The effects of cyclicalmovements are magnified when thebrick are laid in stack bond becausethe tensile bond between the mortarand the brick is not great; much ofthe strength of a wall comes from the

interleaving of brick resulting fromstaggered head joints. In stack bondwork, poor tensile bond strengthmust be overcome by installing continuous reinforcement at no morethan 18 inches on centers, vertically,in the bed joints of the brick masonryas per ACI 530 and other buildingCodes. This technique is also effec-tive whenever tensile strength mustbe increased, regardless of the bond pattern.

Since expansion cracks often occurnear corners, one logical location for amovement joint is at the first head jointfrom a corner (Point #1 in Figure 5).Unless they are installed as a remedialmeasure, movement joints are rarelyfound at corners, primarily for aestheticreasons. They are usually placed twoto ten feet from the corner (Point #2in Figure 5), where, in buildings withshelf angles, the movement joint maycoincide with the window jambs tohelp to disguise the presence of the

Relative Expansion

Rel

ativ

e E

xpan

sion

Crack

Figure 4

Figure 4

Figure 5

5

joint. When the veneer is supported onshelf angles, vertical movement jointsmay be placed virtually anywhere thedesigner decides that they are neededbecause the horizontal movementjoints at the shelf angles divide thefacade into relatively small, discrete,regular sections.

If the masonry is carried acrossopenings by lintels, it is best to avoidplacing vertical movement joint at thejambs of the openings. Instead, placethem several feet from the jambs.Although movement joints are oftenplaced at the jambs with no ill effect –this detailing “works” – more conserva-tive design suggests placing the movement joints well away from jamblines and the ends of the lintels.

Do not place vertical movementjoints at the end of lintels.

Another critical point for crack con-trol is at offsets in walls, such as at Ain Figure 6. Since A is short and rigid,it can easily be cracked by the rota-tional effect caused by the movementof the two long walls. A movementjoint should be placed at the insidecorner. The only time this is not true is when the next movement joint ineach long wall is less than 10 feet fromthe corner.

Long sections of masonry withpunched openings with headssupported by lintels should includevertical movement joints to guardagainst shear cracks forming at thetop corners of windows (Figure 7 ) ordiagonal cracks forming at piers.Stresses develop as the masonrybelow the windows, which isrestrained from moving by the pres-ence of the foundation, expands andcontracts less than masonry abovethe windows. As the band of mason-ry above the openings is much longerthan the bands of masonry betweenthe openings, the total expansion ismuch greater and shear stresses aregenerated. These stresses arerelieved when the crack forms.Remember, if lintels span the headsof the windows, the movement jointsshould not coincide with the windowjambs.

Where adjacent sections of a walldiffer in height and cross-section, thesections will respond to changes in

temperature at different ratesbecause thinner, shorter sections will warm faster than taller thickersections.To reduce the likelihood ofcracking, movement joints are placedat the point where the cross-sectionof the wall changes (Figure 8).

In steel or concrete frame struc-tures, one typical movement jointlocation is at a column. This locationis not always necessary but may behelpful to the contractor. The brickveneer must be anchored to the col-umn in such a way to allow verticaland horizontal movements and toallow the movement joint to function.One method is shown in Figure 9.Since the ties between the veneerand the back-up transfer wind forces

to the back-up, the back-up systemmust also be tied to the columns in amanner which transfers wind loadswhile allowing vertical move-ment to occur. Construction tolerancesare rather fluid and the attachment of the veneer to the column at amovement joint should include a tiefor the end of each veneer panel.

Although movement joints in brickveneer and control joints in the blockback up may align, it is not necessaryfor them to do so, and they can beplaced where ever the design dictates.One advantage of aligning the twojoints is that it may make constructionand inspection easier.

(a)

(b)Expansion Joints

Figure 6

AB

B

Figure 6

EXPANSION

EXPANSION

Figure 7

Figure 7

EXPANSION JOINT

OPENING

(b)(a)

Figure 8

Figure 8

6

VERTICAL MOVEMENTS(Elastic and plasticdeflections)

As mentioned earlier, movementsoccur in the vertical direction as well asthe horizontal, but while horizontal wallsegments tend to move at both endsfrom a stationary midpoint, vertical wallsegments expand upward from rela-tively stationary supports and contractdownward toward these supports.Many building codes limit the verticalspans of brick veneer to 30 feet orless. The practice of supporting brickveneer on shelf angles at each floorlevel requires the installation of move-ment joints beneath each shelf angle.The shelf angles themselves should besized and anchored to carry imposedloads such that total displacement ofthe toe of the angle is limited to L/600or 0.3", whichever is less.

One detail for a supporting shelfangle is shown in Figure 10. Theexpansion gap size is dictated by thetotal amount of movement caused by:

1. Thermal expansion and contrac-tion of the veneer below.

2. Moisture expansion of thebrickwork below.

3. Freezing expansion of thebrickwork below.

4. Elastic deflections of the shelfangle, supporting beam, span-drel, slab edge and columns.

5. Plastic deflections (creep) ofvertical members, particularly inconcrete masonry and reinforcedconcrete buildings.

6. Thermal frame movements.

Note: A steel frame erected at 80º Fwill shrink substantially if exposed to30º temperatures in the winter.

Creep is the continuing shorteningof a member under constant loading –a plastic deformation. Creep usuallyoccurs over a relatively long period oftime. When Portland cement concreteproducts, which are particularly proneto creep, are fully cured, membersloaded in compression actuallysqueeze or flow together. The speedof this flow is greatest at first, andcontinues, but at a decreasing rate,for several years. The total amountof creep depends on the concrete

strength, the intensity and duration ofloading, and the size of the member.

As an example, if we assume thata 10 story building with 10 feet storyheights has a creep value of 0.05" perfloor, the total creep would be 0.5".If there were shelf angles supportingbrick veneer at every floor level, theexpansion gap under each shelf anglewill close permanently by 0.05" (almost1/16"). Added to other movements, thisshrinkage reduces the serviceability ofthe structure if not considered duringdesign. If shelf angles are placed everythree stories (30 feet), then each gapwould close by 0.15" (more than 1/8")from column shortening alone. Creepalso affects concrete beam deflections,which are in addition to the columnshortening.

ShearAnchor

Control(Shrinkage)Joint

VeneerMovementJoint

MOVEMENT JOINT AT COLUMN

Figure 9

MOVEMENT JOINT AT COLUMN

Figure 9

Anchor

Face of beamor slab

Cavity

Weepholes

Sealant

Foam backer rod

Compressible filler

Shim as required

Flashing takento exterior ofwall

Figure 10

Figure 10

Soldier Stretcher

SPECIAL SHELF ANGLEUNITS

Figure 11

SPECIAL SHELF ANGLE UNITS

Figure 11

7

SHELF ANGLES ANDLINTELS

While both are usually formed withhot-rolled steel angles, shelf anglesand lintels are very different. In bothcases the weight of the masonryveneer above the steel angle bears onthe angle. When a lintel is used, theweight of this masonry is transferredto the jambs of the opening below thelintel. Shelf angles act in a differentway: Shelf angles do not rest on thejambs of the openings below, they areattached to the building frame. Thusthe weight of the masonry above ashelf angle is transferred the buildingframe and the masonry in the jambs ofthe opening below carry no load otherthan the weight of the jamb itself.

LIPPED BRICKWhen all of the vertical movements

are taken into account, the movementgap at each shelf angle is usuallyabout 1/2 inch thick (tall) when built.The shelf angle is 7/16 inch or 1/2 inchthick. Thus, the thickness of the horizontal joint at the shelf angle is aninch or more thick. Although the movements discussed may narrow thisgap somewhat, the gap is wider thancorresponding bed joints and is visuallyobjectionable. Special shelf units(lipped brick) detailed in Figure 11 caneliminate this objection (Note that, inmost instances, lipped brick cannot be used with lintels). Remember thatspecial lipped corner brick are neededat corners. Extending the flashing tothe face of the brickwork is difficultwhen lipped brick are used and somedesigners turn the lipped brick upsidedown to allow easier placement of theflashing. This practice should be avoided since the lip is very close tothe toe of the shelf angle and contactmay damage the brick. Another optionis to place the flashing and weepholesin the mortar joint above the firstcourse of brick resting on the shelfangle. If this option is used the spacebetween the angle and the flashingshould be filled with mortar to supportthe flashing and prevent collectionof water.

Glen-Gery makes lipped brick tomatch both molded and extrudedbrick. Lipped brick should not be field

cut since over-cutting in either directioncreates a weak point in the brick whichmay result in cracking the lip itself.Also, corner brick cannot be cut in thefield unless a mitered corner is accept-able. The presence of the shelf anglemay also be disguised by corbeling thecourse of brick immediately above theangle to create a shadow line.

PARAPETSParapets require special considera-

tion because they are exposed to moreenvironmental changes – temperaturechanges, wind loads, and rain andsnow – than the walls below. Both themagnitude and the rate of change ofthe environmental factors are greaterfor parapet walls than for the wallsbelow. Also, the direction of changemay be very different. Therefore, verti-cal movement joints in the parapetshould be no more than 20 feet apartunless each masonry wythe is rein-forced. Corners and offsets remaincritical locations that must be protect-ed. Figures 12 and 13 show severalsuggested details concerning properparapet wall design. Note that thesefigures do not show all elements ofeither detail.

Figures 12 and 13 show an airspace which is continuous past theroof edge. This eliminates a shelf angleand reduces the likelihood of efflores-cence and staining. The vertical legsof metal caps should cover at leastfour inches of the masonry. The metalcoping shown in Figure 12 forms animpervious cap which is considered an

external flashing. Masonry copingstend to be more susceptible to waterpenetration, require through-wallflashing, and may require moremaintenance because of reliance uponsealants in movement joints betweenadjacent members. Note that coveringthe exposed face of the backup withan impervious membrane for the entireheight of the back-up wythe may trapmoisture within the back-up wythe and

SealantSealant

Drip Drip

Metal snap-on coping

Figure 12

Anchor

Drip

Precast-concreteor stone coping

Sealant andbacking rod

Flashing

Figure 13

Figure 12

Figure 13

Ties

Weepholes

Flashing

Concrete fillor grout

Damproofing

Figure 14

Figure 14

8

reduce the durability of both themasonry and the impervious mem-brane. If a membrane does cover theback-up wythe, the height of the para-pet should be no more than 16".

Other coping materials can be usedwith these systems. Cast stone, con-crete, natural building stones, terracotta and brick must be laid with aflashing, must be anchored to thestructural back-up, and must have asoft joint placed between the bottomof the coping and the top of the brickveneer. Always separate veneers fromelements rigidly attached to the back-up system. Through-wall flashings arerequired not only because these cop-ings are permeable, but because themany joints of these copings maydeteriorate and fail, allowing moisturepenetration. Masonry copings shouldincorporate the largest units availableto limit the number of joints at the topof the wall and thus the likelihood ofmoisture penetration. The mortar jointsbetween large rigid caps such as stoneor concrete should be raked andcaulked to reduce potential moisturepenetration at bond breaks. Flashingshould be installed immediately belowthe cap. The cap should include aminimum 15º slope and, on the lowside, project past the face of the wallbelow with a drip a minimum of 1"from the face of the wall. Stone,concrete, and cast stone copings maycontain soluble components which, inthe absence of a flashing under thecoping, may stain the masonry below.

PART TWO:WATER PENETRATION

For most of our history, brickmasonry has been used as a structuralmaterial, laid in multiple, tied wythes toprovide the major support for the floorsand roof of a structure. Only in thiscentury has this changed; the use ofreinforced concrete and steel framinghas eliminated the need for load-bearing brick masonry and we com-monly use only a single wythe of brickmasonry to clad buildings. Multiple-wythe brick masonry is water resistantbecause of its great mass. It must rainvery hard for a very long time before12" or 16" or 24" of brick masonry can

be so saturated with water that thewater appears inside of the structure.Four inches of brick masonry, the usualnominal thickness of a brick veneer, willnot keep the water out all of the time;the mass of masonry is not so greatthat it can absorb all of the water towhich it is exposed before penetrationthrough the brick wythe occurs.

Designers have long recognized thischaracteristic of single-wythe veneersand have developed the “drainagewall” system to accommodate it.The concept of the drainage wall isrelatively simple (Figure 14): A spaceis maintained between the back of thebrick wythe and the face of the back-upmaterial so that water which penetratesthe veneer cannot reach the back-upsystem. As there are places wherethere are paths to the back-up system,at shelf angles and at the bases ofwalls, for instance, a flashing isinstalled to collect water at theseplaces. So water does not fill up the airspace (cavity), weepholes are placedon top of the flashing at the base ofthe air space to drain water from thewall. Critical to the performance of this system is maintaining a clear spacebetween the back of the brick wytheand the face of the back-up system or

the face of any insulation or othermaterials applied to the face of theback-up.

A further development of thedrainage wall system is the rain screenwall. Water may be driven throughbrick masonry because there is an airpressure difference between the twosides of the brick wythe. If there is noair pressure difference, very little waterwill pass through the masonry. In a rainscreen system, the air space is ventedat the top and bottom and horizontallycompartmentalized to allow any differ-ences in pressure to be equalizedquickly. Once pressure differences areeliminated little water will pass througha properly designed and constructedbrick wythe. Rainscreen walls arevery specialized in both design andconstruction and are beyond thescope of this publication.

DESIGN AND SPECIFICATIONOF DRAINAGE WALLS

One of the most effective methodsof reducing the amount of water thathits a masonry wall is to use over-hangs to protect the walls. This isparticularly easy when pitched roofsare used. Gutters and downspouts

Window

Sealant

Brick Sill

Flashing

Figure 15

Figure 15

9

should be installed where other meansof roof drainage have not beendetailed. When the roof is flat, over-hangs can be incorporated by extend-ing the ends of the joists, but a moretypical detail is a gravel stop or parapetwall. When a gravel stop is used, it isimportant that the gravel stop be highenough to retain water on the roof untilit can drain off through the roof drains.

Parapet walls (and garden walls)must be capped to close the top ofthe wall. While brick masonry caps arevery attractive, they present manyopportunities for leakage and deterio-ration unless they are designed andinstalled very carefully. Masonry capsmust be pitched to drain, have fulljoints, and be securely anchored to thewall below. A flashing and adequateanchoring system must be placedbelow masonry caps (Figure 13). Inaddition, a minimum 1" overhang anddrip notches are recommended for allmasonry caps. Glazed brick must notbe used to form a cap.

When a metal cap is used,

1) the top must be pitched to drain,

2) the vertical legs of the cap mustcover at least four inches of brickmasonry, and

3) a drip must be formed at thebottoms of the vertical legs(Figure 12).

The primary function of a windowsill is to keep water draining from win-dows or other impervious materialsfrom running down the face of themasonry. Many other siding materialsas well as windows and doors absorblittle or no water, allowing most of thewater to flow over the sill or cap below.All sills must have a minimum pitch of15º (about 1/4" to the inch), mustincorporate a drip edge or notch andshould have as few joints as possible.Wind pressure on flat sills tends toincrease water penetration, leading todeterioration of the sill or surroundingmaterials. Because of the absence ofsunlight on north elevations, very deepsills receiving large amounts of waterwill remain wet, promoting organicgrowth and the accretion of dirt. Aswith wall caps, a flashing must beplaced under all sills (Figure 15).

It is important to pitch the gradearound the structure so that surface

water is directed away from the building.Down spouts should not be dischargedat the base of the wall, but, at a mini-mum,should be directed onto splashblocks and away from the building.

The key to the drainage wall systemis to keep water from moving from theback of the veneer to the face of theback-up. The space between theveneer and the back-up – the airspace – must be kept clear of mortarand other debris so that water has nopath from the veneer to the inside ofthe structure. Wider air spaces, twoinches, for instance, are easier to keepclean than narrower spaces and arerecommended by many authorities.One way to keep the air space clean isby clearing the mortar droppings fromthe cavity by placing a board in thecavity and drawing it out as each tielocation is reached. Spreading themortar so that the inside of the bed isthinner than the outside will reduce thevolume of mortar droppings. Proprietarysystems are also available to helpmaintain a clear air space.

FLASHINGSChanges in the details of the wall

cross-section often allow materials tobridge the air space, providing a path-way for water to reach the interior ofthe building. This routinely occurs atshelf angles, lintels, load-bearing floorslabs, and at grade. To prevent thisflow of water, a flashing, a flexible,impermeable material, is installed. Theflashing both collects water and pro-tects materials behind and below itfrom this water (Figure 14). Counterflashings, flashings under caps, andflashings under sills pr

e v e n t w a t e r f r

entering the veneer. Flashings overwindow, door, and louver heads, flash-ings at the bases of walls and at shelfangles, and flashings over and underother building materials all collect waterand prevent it from entering theremainder of the structure. Except forcounter flashings, which are usuallyinstalled in a reglet at the face of thewall, these flashings are usuallyinstalled as through-wall flashings –

Optionallowerflashing

Flashingwithend dam

Weephole

Flashing end dam

Weepholes

Weepholes

Area of potentialwater penetrationif optional lowerflashing is NOTinstalled

Optional lower flashing

Figure 16

Flashing end dam

Figure 16

10

flashings laid in or attached to theback-up which then drop down atleast eight inches, run horizontally, andthen pass through or under the brickwythe to the outside.

Flashings in masonry abovestepped roofs, above bay windows,and around chimneys are oftenattached to the face of the wall witha reglet. Flashing systems in theselocations must include through-wallflashings that collect water from behindthe brick wythe (Figures 17 and 18).

Rigid flashings for single wythe chim-neys can be formed with short overlap-ping flashings. Flashings in multi-wythechimneys must incorporate flashingswhich terminate in the back-up.Flashings from the face of the chimneyto the roof may be attached to theface of the chimney or tucked belowthe through-wall flashing (Figures 17and 18).

Traditionally, heavy copper, lead-coated copper, and stainless steelwere the materials of choice and they

remain so. Because the basic materialsand fabrication are so expensive, thesematerials are now little used. Most ofthe flashings installed today are plas-tics, fabric composites, and compositemetal flashings. A very common flash-ing material that should be avoided isPVC (poly-vinyl-chloride). PVC flashingshave a limited life span, as short as fiveyears in a wall system that is expectedto last for many years. Other materials,such as bitumen polymers, EPDM,fabric composites, or thin metal com-posites with cores of either aluminumor, preferably, copper, are preferred.Neither #15 or #30 building felt norpolyethylene sheeting may be usedfor flashings.

Although most flashing details willshow the flashing forming a drip at theface of the wall, this is only possible ifone of the rigid flashings is used.Plastics, composites, and thin metalcomposites cannot be formed into adrip and are difficult to hold in astraight line. One popular option is torequire the mason to extend the flash-ing beyond the face of the wall andthen cut it flush to the face of the wall.The details of many flashing manufac-turers indicate that the flashing shouldbe held behind the face of the wallabout one-half inch. When this is done,the water will run under the flashingand into the core holes or back intothe wall. Avoid these details.

Continuous flashings, such as occurat shelf angles and at the bases ofwalls, must be lapped and sealed inaccordance with the flashing manufac-turer’s instructions. This often involvesthe use of a special mastic or adhe-sive. Do not use roofing cement. Caremust be taken at inside and outsidecorners to insure that water cannotbypass the flashing and enter the wallsystem. Discontinuous flashings, suchas those over a lintel, should extendbeyond the end of the lintel. The endsof discontinuous flashings must beturned up into a head joint, forming adam to prevent water from runningfrom the end of the flashing and backinto the wall (See Figures 16 and 20).

Flashings above curved arches orpitched roofs are often omittedbecause there is no obvious way toinstall the flashings. One practicalmethod is to install short lengths of

Cricket

Shingles

Weepholes

Heat resistant caulking

Airspace

Flashing

Chimney cap

Sealant

Clay flue liner

Chimney flashing

Roof flashing

Figure 17 CHIMNEY SECTION

CHIMNEY SECTION

Cricket

Shingles

Roof flashing

Chimney flashingw/ weeps

CMU

Airspace

Flue liner

Figure 18

Figure 18

Figure 19

Stepped flashing

End dams

Figure 19

Figure 17

11

through-wall flashing above and alongthe line of the arch or lower roof.Each flashing has end dams and theupper flashings overlap and shieldthose below, protecting the building(See Figure 19). A single level of flash-ing can also be used successfully if thearea of masonry between the flashingand the arch is small.

WEEPHOLESWeepholes provide a path out of the

wall for the water collected by theflashings. The easiest way to form aweephole is to space open head joints24" apart, directly on top of the flash-ings. Weepholes located a course ormore above the flashings are of littlebenefit. Many designers do not like theshadow created by using open headjoints for weepholes and a number ofvents, screens, and multi-celleddevices are available to disguise thepresence of these weepholes. All ofthese may be spaced 24" apart.Cotton wicks – not nylon or other syn-thetics, they do not “wick” – may alsobe used. Three-eighth inch cottonclothesline works well, particularlywhen draped over the first set of tiesabove the flashing. Wicks should bespace no more than 16" apart. Do notuse 3/8" plastic tubes; they are easilyclogged during construction. Somedesigners and contractors placed twoto four inches of unbroken pea gravelat shelf angles, at lintels, and at thebase of the cavity to prevent weep-holes from being clogged by mortardroppings. This can be an effectivetechnique unless the volume of mortardroppings is such that a continuousbarrier of mortar is formed on top ofthe gravel, or mortar dropping on thegravel bridge the airspace above thetop of the flashing. When this occursthe effective freeboard of the through-wall flashing is reduced and water canhave easy entry to the interior of thestructure. Care in material selection isimportant because fractured stonescan cut the flashing. Also, the weightof the gravel may stretch and tear theflashings, particularly at shelf anglebolts or at lintels where the flashing isnot continuously supported. A numberof proprietary systems also serve thisfunction and claim to avoid the disad-vantages of gravel.

GLAZED BRICKBecause water cannot escape

through the face of a glazed brick, theevaporation of water through the faceof the masonry is severely limited andlarge amounts of water may betrapped in the veneer. This reservoir ofwater may affect the durability of themasonry and it must be eliminated.The loss of surface evaporation mustbe balanced by designing an air spaceat least two inches wide and incorpo-rating open head joint weepholes atthe bases of air spaces and open headjoint vents at the tops of air spaces.Individual weepholes and vents shouldbe no more than 24" apart horizontally.Obviously, it is mandatory that the airspace be kept clean so that air canmove freely.

MORTARThere are two rules for mortar

selection:

1) No one mortar is best for everypurpose and

2) Use the weakest mortar type thatwill do the job.

Portland cement/hydrated limemortars provide the best resistance to water penetration and Type “N”Portland cement/lime mortars providethe greatest water penetration resis-tance. Type “S” mortar may be usedwhere greater flexural tensile strengthis important; primarily where bending

stresses may be high. Type “S” mor-tars may be helpful when floating is aproblem or when the bricks have avery low initial rate of absorption (suction). Type “S” mortars have lowerwater penetration resistance, are notas workable, and are more expensivethan Type “N” mortars.

JOINT TYPESThe configuration of the mortar

joint affects the resistance of the jointto water penetration (Figure 20).Concave, vee, and grapevine jointsprovide the highest resistance to waterpenetration. All other joint profilesshould not be specified for exteriorwork.

WORKMANSHIP

STORAGE OF MATERIALSAll masonry materials, including the

masonry units, cement, lime, sand,coloring pigments, water, ties, andanchors, must be stored off of theground to prevent damage, contami-nation, or absorption of water. It isparticularly important to cover themortar materials to prevent hydrationand to cover the masonry units andsand to avoid water absorption andfreezing during cold weather.

WEATHER EXTREMESWhen it is very hot or very cold,

special care must be taken during con-struction. Also, temperature extremesare exaggerated when it is windy.

When it is hot and dry, mortar readilyloses water to evaporation, quicklybecomes unworkable, and loses itsability to bond to any masonry unit.Mortars with the ability to retain water,such as mortars containing hydratedlime, should be used. If a brick has afield measured initial rate of absorption(suction) in excess of 30 grams, thisloss of bonding ability is accelerated.In hot, dry conditions, these brickmay have to be wet before laying.Immersing a cube of brick in water theday before laying or use of perforatedhoses works well. The brick must besaturated but surface dry before laying.

Concavejoint

Grapevinejoint

Vee joint

Figure 20

Figure 20

12

When it is cold, the bricks andmortar components must be kept fromfreezing, the work must be coveredwith insulating blankets, and, depend-ing upon conditions, the work mayhave to be enclosed and the spaceheated. Follow the recommendationscontained in BIA Technical Note #1.

MIXING MORTARMortar makes up about 20% of the

area of the face of a wall laid with stan-dard modular size brick.Since changesin the color of the mortar will changethe appearance of a wall, consistentand accurate proportioning of mortarmaterials is important. This consistencyand accuracy cannot be achieved bysimply counting the number shovels ofsand that go into the mixer. A proce-dure must be developed to assure thatthe same volume of sand is put in themortar mixer for each batch of mortar.Cubic foot boxes and five gallon buck-ets are often used for this purpose.Specific requirements for mortar mixingare found in ASTM C 270, StandardSpecification for Mortar for UnitMasonry.

MORTAR LIFEMortar becomes stiff in two ways:

1) Water evaporates and the mortar isno longer plastic and 2) the chemicalreaction with water (hydration) causesthe mortar to become stiff or hard. Thechemical reaction reaches initial set inabout two and one-half hours andunused mortar must be discarded atthat time. Water may evaporate at anytime and cause the mortar to be comestiff and unusable. Rather than throwthe mortar away, water can often beadded to restore the plasticity of themortar. This is called “retempering.”Two notes of caution: Retemperingmay lighten the color of mortar andretempering will reduce compressivestrength slightly. While any change inthe color of the mortar is a concern,changes in compressive strength areusually minimal and the workabilitygained by the addition of water far out-weighs the small loss of compressivestrength when laying a veneer (a non-loadbearing wythe).

FULL HEAD AND BEDJOINTS

It is vitally important that joints befull. If head and bed joints are not fullof mortar, the effective thickness of thewall is reduced, thereby decreasing thewater penetration resistance. Poorconstruction techniques often lead tounfilled joints. While specifications usually require full joints, the only sureway to get full head joints is for thespecification to require that one head ofeach brick be buttered with mortar andthe brick then be shoved into place.

CLEANINGThe clays, shales, additives, and

coatings used to manufacture a brickall determine how a brick must becleaned. The presence or absence ofa colored mortar or manufactured ornatural building stones all affect howa masonry wall must be cleaned.Consult the manufacturer of eachmasonry product before establishingor accepting a cleaning method.

As time passes it becomes moredifficult to remove hardened mortar,particularly when the mortar is in largelumps. Brush down the wall with a stiffbristle brush each time the scaffold israised and at the end of each day orshift to remove large lumps. Type “N”mortars should be cleaned withinfourteen days of laying the brick; Type“S” mortars within five to seven days.

The bucket and brush method isthe preferred method. Pressure washers, while they may be useful forwetting and rinsing can cause immensedamage if used to apply chemicals orto remove smears and snots.

Remember:

1. Never use muriatic acid.

2. Chemicals that are not acidic willnot remove hardened mortar.

3. Metal tools of all types maydamage the walls.

4. Test all materials and methodsthoroughly. Allow the test areasto dry before accepting a chemi-cal and method.

5. Always wet the wall thoroughlybefore applying chemicals andkeep it wet – with water or thecleaning chemical – during thecleaning process.

6. Rinse the wall thoroughly.

EFFLORESCENCEEfflorescence is a deposit of soluble

salts on the surface of the masonry.Without water, efflorescence cannotoccur. The thrust of preventative mea-sures for controlling efflorescence is tocontrol water in the masonry becauseefflorescence is only the symptom ofthe underlying problem – the presenceof water. In most cases, these salts are extremely soluble in water andacids or special chemicals are notneeded to remove them; only anabsence of water and the passage of time are needed.

New buildings sometimes becomestained with efflorescence. This stain-ing is called new building bloom and isusually the result of water enteringunprotected walls during construction,but may also be caused by the waterin mortar or grout. New building bloomis best handled by waiting for thebuilding walls to dry over a heating orcooling season and then allowing rainsto wash the salts from the walls.

The appearance of efflorescence inolder buildings is a symptom of achange in the way that the structurehandles water. Eliminating the flow ofwater into the masonry will solve problems with efflorescence.

A common time for efflorescenceis in later winter or early spring. Thishappens because water tends toremain in walls for a long time at thistime of year – there is no extra heat toevaporate the water – and the waterhas a long contact time with the build-ing components. Thus, chemicals thatmight be considered “insoluble’’ inwater reveal their slight solubilitybecause of the long contact times.Again, the solution is to deny wateraccess to the walls. Because thelocation of the dew point is moved,efflorescence may also appear afterHVAC system change over.

Corporate OfficeGlen-Gery Corporation1166 Spring StreetP O Box 7001Wyomissing, PA 19610-6001

Phone: (610) 374-4011Fax: (610) 374-1622

http://www.glengerybrick.comE-mail: gg@glengerybrick.com

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