Jeff Bowlsby CCS, CCCA
Exterior Wall and Stucco Consultant
Licensed California Architect
Stucco and Sealant
An exterior stucco wall cladding system does not need sealant or caulk for its own needs, but sealant or caulk is significant if not critical to the effectiveness of the exterior building enclosure system as a whole, for which the exterior stucco wall cladding system plays an integral part.
Water intrusion through building enclosure systems is a major cause of property damage, a catalyst for legal action and liability exposures for all parties and conditions related to building enclosures in general and exterior stucco wall cladding systems in specific. Let us not forget that issues concerning sealant decimated the EIFS industry, but the EIFS cladding material itself was not especially problematic. We cannot let history repeat itself and be myopic regarding stucco. Stucco wall cladding systems may be headed in the same direction as EIFS if the omission of sealant causes even the perception that water-related issues may be related to the stucco exterior wall cladding system. The possibility of water intrusion associated with stucco wall cladding systems can be minimized with the careful, considered and strategic use of sealant or caulking.
The use of sealant or caulk at stucco clad weather-exposed surfaces at lath accessory joint splices, intersections, terminations, and at stucco panel edges to prevent water penetration, although granted could be stated more clearly, is reasonably inferable as a building code requirement and Minimum Stucco Industry Standard, and has strong support by significant reference resources in the stucco industry.
Visit the StuccoMetrics Reference Archives webpage for cited references and further information.
ASTM C1063 Standard Specification Installation for Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster(1:
· (7.11.3) Casing Beads: Terminate plaster at panel edges and at dissimilar materials with casing beads. Provide separation gap between plaster panel edges and dissimilar materials to isolate non-loadbearing members from loadbearing members / penetrating elements and prevent the transfer of structural loads.
ASTM C926 Standard Specification for Application of Portland Cement-Based Plaster(1). This text has not fundamentally changed since the first edition of C926 in 1986 and before that in its predecessor ANSI A42.2-1971 Portland Cement and Portland Cement-Lime Plastering Exterior (Stucco) and Interior(2):
· (A2.1.3) Seal separation gaps between weather exposed plastered panel edges and dissimilar materials to prevent water penetration.
In addition, various other stucco industry reference resources establish a strong precedent for sealant use with stucco wall cladding systems, assemblies, subassemblies and components including embedment of lath accessory splices, intersections and terminations, to keep bulk water out of the exterior stucco wall cladding system. The following reference resources should be considered advisory because they are either for historical reference and have been superseded by more current reference resources from the same organizations, or are not codified in the Minimum Stucco Industry Standards:
· 1971 ANSI A42.3 – “A2.1.4 On exterior work V-grooves shall be caulked or sealed to prevent entry of water.”(2)
· c.1980 Technical Manual, Keene Corporation, Penn Metal Products(3): “On vertical surfaces it may mean the installation of caulking or weatherstrip beneath the control joint to seal the opening…”
· c.1980 Control Joints in Exterior Portland Cement Plaster, Western Conference of Lathing and Plastering Institutes, Inc.(WCLPI)(4): “All intersections and terminations of control joints should be embedded and weather-sealed with caulking.”
· 1981 Minimum Property Standards, US Department of Housing and Urban Development (HUD)(5): Required compliance with 1971 ANSI A42.3, as discussed above.
· 1983 Keene Corporation product catalog(6): “Intersections of “joints” may be butted-and-calked...”
· 1991 920-91 Guide Specifications for Metal Lathing and Furring, Metal Lath/Steel Framing Association (ML/SFA Division of NAAMM)(7): “All intersections and terminations of “control joints” should be embedded and weather sealed with caulking.” Drawing entitled “Control Joint Intersections” depicts two control joint intersection conditions, both indicating sealant at the intersections. Drawing entitled “Screwable Steel Framing” depicts multiple locations of sealant caulking at stucco panel perimeters to adjacent construction.
· 1993 Guide to Portland Cement Plastering, ACI 524R(8), American Concrete Institute: “Joints, intersections and terminations of control joints, should be embedded and weather-sealed.” “Terminations or splices in “stress-relief joints” should be embedded within a weather-resistant elastic sealant to prevent moisture penetration.”
· 1996 Portland Cement Plaster (Stucco) Manual, EB049 Portland Cement Association(9): “All joints, intersections, and terminations of control joints should be embedded and weather-sealed.”
· 1997 Stucco Resource Guide, Northwest Wall Ceiling Bureau(10): “4.6 Control members shall be fit together neatly at intersections and splices and shall fit neatly at terminations. In wet areas, splices and intersections should be set in sealant or buttons of sealant should be applied after control joint installation.”
· 1999 Stucco Resource Guide, Northwest Wall Ceiling Bureau(11): “21. It is recommended that trim accessory joints be weather-sealed by embedment in caulking at intersections, when placed end-to-end, abutting one another and at terminations.”
· 2001 Systems Manual, Texas Lathing and Plastering Contractors Association & the Texas Bureau for Lathing and Plastering (12): “21. It is recommended that trim accessory joints be weather-sealed by embedment in caulking at intersections, when placed end-to-end, abutting one another and at terminations.”
· 2003 Portland Cement Plaster (Stucco) Manual, EB049 Portland Cement Association(13): “All joints, intersections, and terminations of control joints should be embedded and weather-sealed.”
· 2004 Guide to Portland Cement Plastering, ACI 524R, American Concrete Institute(14): “Terminations or splices in the control joint should be embedded within a weather-resistant sealant to prevent moisture penetration.”
· 2007 Stucco in Residential Construction, Minnesota Lath and Plaster Bureau(15) (2000, 2004 editions identical): “The subsequent joint between the window and stucco at the sill and jambs are then filled with a closed cell bond breaker and low modulus elastomeric sealant [illustrated].” Various illustrations of stucco wall cladding system openings and penetrations including deck attachment, deck handrail attachment, piping and vent sleeves, hose bibs and dryer vents, light fixtures and outlets depicted and described as sealed.
· 2008 Guide to Portland Cement Plastering, ACI 524R, American Concrete Institute(16):
è “Terminations or splices in “stress-relief joints” should be embedded within a weather-resistant elastic sealant to prevent moisture penetration.”
è “Specify and detail the installation of flashing, weep screeds, and sealant at doors and around windows, vents, and all other wall penetrations to ensure that water will be diverted or channeled to the outside of the wall assembly in accordance with ASTM C1063 and E2112.”
è “Specify and detail the use of sealant at “stress-relief joint” terminations and splices”
è “Specify and detail the use of sealant at wall penetrations to prevent leakage at these points.”
· 2009 AMICO product catalog(17): “Flashing should be applied in the form of asphalt saturated construction paper or flashing strips behind all expansion joints and all joints should be imbedded [sic] in caulk.”
· 2009 Guide Specifications for Metal Lathing and Furring, EMLA 920-09(18), regarding sealant use at metal lath accessories:
è “Joinery of abutting ends of trim accessories should be spliced or lapped and sealed with appropriate sealant.”
è “Joinery of “control joint” intersections should be spliced or lapped and sealed with appropriate sealant.”
è “Joinery of flashing sections should be appropriately lapped, sealed and mended together by applications of sealants, adhesive backed membrane or other appropriate means of continuity.”
è “Stucco terminations at penetrations should be sealed with sealant to the metal side of the flashing or stucco trims. Not to the face of the brown coat or finish coat.”
è ““Control joints” should be sealed at inside/outside corners and termination points.”
è “All intersections and terminations of “control joints” must be embedded and weather-sealed in a bed of caulking material.”
· 2009 Lath Inspection Resource Manual, Second Edition, Minnesota Lath & Plaster Bureau(19) (2005 Edition identical): General Notes, “Joinery of abutting ends of trim accessories should be spliced or lapped and sealed with appropriate sealant.” “Joinery of control joint intersections should be spliced or lapped and sealed with appropriate sealant.” References on numerous detail photos of stucco panel edges, “control joints”, “expansion joints”, splices, intersections and terminations, pipe and vent flashings, be sealed because they are “vulnerable to moisture intrusion”.
· 2011 Plaster Assemblies Manual Online, Technical Services Information Bureau (TSIB)(20): “It is recommended that in areas subjected to wind-driven rain, control and expansion joint terminations/intersections be set in sealant or buttons of sealant for wet locations.”
· 2014 Fasteners and Self-Sealability of Weather-Resistive Barriers, RCI-TA-005-2014, Roof Consultants Institute Technical Advisory(21):
“The potential for water intrusion through fastener penetrations—particularly with claddings like siding, stucco, and adhered masonry veneer, where thousands of fasteners can be used to attach the siding or metal lath through the air barrier—can be minimized by following common practices as follows:
è Confirm fasteners engage with studs/framing or a sound substrate.
è Avoid the use of supplemental fasteners, sometimes used incorrectly to attach accessories between studs such as control joints and other accessories in stucco (required to be wire tied between studs).
è Avoid errant fasteners that do not go through studs or spin and create a larger opening, as well as loose connections (particularly in gypsum-based sheathing).
è Remove “loose” fasteners and seal the holes.
è Avoid the use of powder or power-actuated fasteners.”
· 2014 Plaster and Drywall Assemblies Manual, Walls and Ceilings Magazine(22): “It is recommended that in areas subjected to frequent wind-driven rain, control joint and expansion joint terminations/intersections be set in sealant or buttons of sealant to prevent moisture intrusion.”
Additionally, review the following ASTM standards for general information about sealant specification, sealant joint design and installation and sealability of fasteners:
· ASTM C1193 Standard Guide for Use of Joint Sealants(1)
· ASTM C920 Standard Specification for Elastomeric Joint Sealants(1)
· ASTM D1970 Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection(1)
· ASTM E2112 Standard Practice for Installation of Exterior Windows, Doors and Skylights(1)
· ASTM E2128 Standard Guide for Evaluating Water Leakage of Building Walls(1)
· ASTM E2266 Standard Guide for Design and Construction of Low-Rise Frame Wall Systems to Resist Water Intrusion(1)
While other stucco industry reference resources are silent on the issue of sealant or caulk at lath accessory splices, intersections and terminations, none specifically recommend against sealant, or require that sealant or caulk not be used for these conditions.
From ASTM C926 the general intent to provide a sealant or caulking material to seal out potential water entry at “V-grooves”, stucco panel exposed ends and edges is clear. The issue is identified and general requirement is explicitly stated.
Significant support exists for the use of sealant or caulk at weather-exposed lath accessories from every facet of the stucco industry including the codified Minimum Stucco Industry Standard ASTM C926, the original “control joint” lath accessory manufacturer, the metal lath and lath accessory product manufacturer association, portland cement product manufacturer organizations, contractor trade organizations, and voluntary industry standards documents.
If every exterior stucco clad building surface was fully-protected from the weather and direct exposure to bulk water especially wind driven rain, then sealants or caulk related to the stucco cladding system would probably not be essential for any exterior stucco wall cladding system. A building would need 100% protection from the weather using extremely broad overhangs, a high performance waterproofing enclosure system (basically an above ground submarine) or similar means to be completely protected. But that is obviously not reality.
Weather reality is that many, many stucco clad buildings experience weather extremes from time to time, if not on a regularly recurring basis. Even climates considered as relatively benign, can experience occasional hard driving rains, windblown into the wall claddings, buildings that may or may not have protective roof coverage or other drainage conditions. Reasonably designed and constructed solutions when it comes to exterior stucco wall claddings will foresee and accommodate reasonably predictable extreme weather conditions.
Cured portland cement-based stucco wall cladding systems are exceptionally weather-resistant, one reason that makes them an excellent exterior building wall cladding system. Where water can potentially penetrate the exterior stucco wall cladding is at discontinuities in the stucco cladding system – at cracks, weather exposed and unsealed static and dynamic movement joints, penetrations, wall openings and stucco panel edges.
Cracks are not only visual distractions; if a crack goes all the way through the stucco membrane it can create a water pathway into the wall cladding system. Any crack that is visible at the finished surface is a potential water path, but cracks may only occur on the surface and not through the full thickness of the stucco membrane. A water molecule only needs a mil or two width to be able to penetrate through a crack. Cracks in one coat, may not align with cracks in subsequent coats. Cracks in one coat stucco applications may be more likely to be through cracks because the coating has only one coating layer, than in a multiple coat stucco wall cladding system. Multiple cementitous coating layers add redundancy so cracks in 2-coat, 3-coat or 4-coat stucco are more likely to be covered by succeeding coats. Minimizing water penetration at cracks is in part, a function of the number of portland cement-based plaster coats and characteristics of each coat, especially the finish coat.
The potential for water penetration into the stucco cladding system is a greater risk at weather-exposed stucco lath accessory joint splices, intersections, terminations, and at stucco panel edges than from cracks. Rigid metal and plastic lath accessories are exposed at the stucco finish surface and are commonly installed with simple butted splices, intersections and terminations that are not inherently watertight. Stucco panel edges at perimeters, are typically constructed with casing beads, which are not inherently watertight to the WRB or adjacent construction, and the separation gap that occurs between the casing beads and adjacent windows, doors, vents, penetrations and the interface with other claddings or wall elements can allow water penetration if the gap is not sealed watertight.
Water penetration into the exterior stucco wall cladding system from any source is hopefully incidental moisture only and not bulk water, but that depends on the specific combination of weather conditions, weather exposures and construction of the exterior stucco wall cladding system. Whether water penetration occurs at cracks, lath accessories or stucco panel edges, a concealed continuous WRB, SAF and sheet metal flashings and weep flashing system is provided to manage incidental water and redirect it out of the exterior stucco wall cladding system.
Preventing bulk water from even entering the stucco cladding system at all is by far the easiest, least costly and most effective means of preventing water intrusion into the building and avoiding the potential for concealed damage, than attempting to manage it once it has bypassed the exterior stucco wall cladding. The strategic and careful application of resilient sealant is the most effective, most durable solution and requires no maintenance when concealed from ultraviolet exposure. Lath accessory splices, intersections, terminations are best embedded into a sealant bed. Sealant at stucco panel edges with adjacent dissimilar materials must unfortunately be exposed and periodically maintained. Most dry lapped WRB and flashings systems used with stucco wall claddings are dimensionally compact, gravity drainage assemblies that may not have the performance capability to effectively manage elevated volumes of water behind the stucco wall cladding system because of their compact dimension. Lath fasteners are jobsite installed and create innumerable fastener penetrations in WRB membranes; any fastener penetrating the WRB that is mis-located, mis-installed or removed without being repaired can potentially allow water intrusion into the wall cavity. Lath accessories are fabricated of metals and plastic, and extend through the thickness of the stucco and are weather-exposed at the surface of stucco. No lath accessory is resilient enough or self-sealing to create a watertight condition at splices, intersections and terminations without the use sealant or caulk.
Stucco panel edges adjacent to dissimilar materials such as at window and door frame assemblies, louvers and vents, and wall penetrations require similar attention with sealant to create a watertight condition. Window and door frame assemblies sometimes include an “integral stucco stop” molded or formed into their perimeter frames intended as a convenience to the plasterer, but they are a disservice because they frequently do not function as necessary to keep bulk water out of the stucco wall cladding. These window and door frame assemblies are often made of aluminum or non-metallic materials, with a coefficient of linear thermal expansion (CLE) that is quite different than stucco. The CLE of stucco and steel are similar, but aluminum is 2x, and PVC is over 4x the CLE of stucco. This difference in thermal expansion rates creates an incompatibility between stucco and these other materials under ambient service conditions which can create separation gaps, stucco cracks and spalling which may allow water penetration at stucco panel edges. Additionally, portland cement-based plaster shrinks away from these perimeter conditions creating similar gaps that can allow water penetration if not sealed or caulked watertight. ASTM C1063 does not recognize the ‘integral stucco stops’ of these assemblies as an acceptable stucco panel edge termination, and requires a casing bead as a stucco panel edge termination, a separation gap and a sealant joint at dissimilar materials to prevent water penetration. Avoid the temptation to omit casing beads and sealant at stucco panel edges adjacent to dissimilar materials such as windows and doors, especially assemblies with ‘integral stucco stops’. Provide a separation gap between the stucco panel edge casing bead and the dissimilar material of at least ¼ in. wide (3/8 in. and wider is a better performance joint) and fill the gap with sealant over a backer rod following ASTM C1193, for cleaning, joint configuration and other sealant joint parameters.
Other conditions of the exterior stucco wall cladding system may exist that may allow water penetration but are not explicitly mentioned as requiring sealant in ASTM C926. These conditions may require sealant or caulking in the same spirit – to keep bulk water out of the stucco cladding and out of the building. Lath fasteners penetrating the WRB or SAF that miss framing members, or that are installed at an angle or are otherwise mis-installed, or are removed and relocated leaving an open hole in the WRB, may cause water penetration if not sealed watertight. Drainage flashings with unsealed laps or intersecting with other lath accessories may create water pathways into the building if not sealed watertight.
Sealant and caulking materials must be resilient, durable and compatible with their substrate, typically either the metal or plastic lath accessories or flashings, or the WRB membrane and SAF. Compatibility of materials must be verified. Movement performance of sealant must be verified. Substrate preparation, cleanliness, the need for primers, sealant joint profile and other factors must be considered and accommodated for the effective use of sealant and caulking materials.
The use of sealant materials is appropriate to seal weather-exposed stucco movement joint lath accessory splices, intersections, terminations against potential water penetration. Stucco wall cladding system movement joints provide a range of motion that is predictable and the movement joint can be designed and sealant material specified to accommodate the required movement. ¼ in. wide sealant joints are the Minimum Industry Standard, but 3/8 in. and wider are easier to install and perform better by accommodating more movement. Wider movement joint widths may be required dependent on anticipated movement requirements. Sealant materials in correctly designed and constructed stucco movement joint subassemblies can typically accommodate a movement range of between 25% to over 100% of the joint width, so joint width and sealant material performance capability are used to determine the design of the joint and its performance. Stucco movement joint subassemblies are located to accommodate various movements – building substrate support movement, stucco panel perimeter movement, movement at the interface between load-bearing and non-loadbearing components, shrinkage movement and thermal movement, etc.
The use of caulking materials is only appropriate for non-movement conditions. Caulk materials are relatively non-elastomeric, and can only realistically be used as a static hole filler where little to no movement is anticipated which is one reason why caulking materials are not typically specified. Most design and construction professionals will specify and use only one sealant material on the jobsite for the purposes described, to avoid the potential for misapplying the wrong product for the wrong purpose. While both movement and non-movement conditions exist related to stucco wall cladding systems, typically sealant materials are used for both conditions for convenience, even though the movement capability of sealant materials are not required for hole filling purposes. Caulking materials will not be discussed further as they have limited function and are seldom used.
ANSI A42.2-1971, predecessor to ASTM C926, at A2.1.4 says: “On exterior work, V-grooves shall be caulked or sealed to prevent entry of water.” ASTM C926 today, at A2.1.3, is virtually identical, and adds “exposed ends and edges of stucco panels or exterior work” to the requirements.
The term ‘exterior’ is synonymous in definition with weather-exposed surfaces in the building code. The concept is simple, exterior building surfaces are weather-exposed and as such require weather protection. Non-weather exposed surfaces do not require weather protection.
That word “V-groove” is antiquated and troubling to some in a contemporary context, but reflective of the terminology used in the era when it was adopted. The 1981 HUD Minimum Property Standards illuminates the term: “Run V-groove on brown and finish coats around all metal trim, and at similar conditions.” So a V-groove would have occurred in the cement coats at metal lath accessories as it abutted adjacent components at stucco panel ends and edges, a V-groove serves the same purpose and is therefore functionally equivalent to a lath accessory today where exposed at the stucco surface. A V-groove is functionally identical to lath accessories which include conditions such as intersections with other lath accessories, at splices, and such as where wrapping internal and external corners. Where occurring at weather-exposed surfaces, V-grooves and equating to today’s lath accessory splices, intersections, terminations, and stucco panel edges were then and are now, prone to potential water penetration and required to be sealed to keep bulk water out of the stucco cladding system.
Water can potentially penetrate around the ends and edges of stucco panels which occur at the top, bottom and sides of a stucco wall cladding, around wall openings such as window and door assemblies, and at penetrations such a pipes and electrical outlets. Each of these stucco conditions – joints, joint terminations, and edges, must include a metallic or non-metallic lath accessory and a separation gap to the dissimilar material to allow for differential movement. The separation creates a stucco panel edge and gap at the stucco panel edge which, at weather-exposed surfaces, needs to be sealed to keep bulk water out of the stucco cladding system. Sealant applied directly to portland cement-based stucco is not durable.
Sheet metal and non-metallic lath accessories are hollow in profile or create a hollow void behind them that even though potentially narrow, is large enough to function as a water path. Once bulk water gets behind the lath accessory it can travel great distances behind the stucco wall cladding until it either drains out from behind the cladding or becomes water intrusion into the wall cavity. It is important for vertically-oriented lath accessories to allow drainage at their lowermost termination, typically over weep screeds or drainage flashings – conditions which should not be sealed to allow drainage.
Fasteners for installing lath and lath accessories – nails, screws and staples – can be especially challenging from a water penetration perspective. On a wall, staple crowns must be installed vertically-oriented parallel to studs so that both staple legs are installed to penetrate vertical stud framing, which can be a physical challenge for an installer. Any fastener installed then subsequently removed leaves a hole in the WRB that is a direct water path into the wall cavity unless it is repaired. Seeing a black hole on black building paper, through shiny, small lath apertures, and effectively sealing them against water penetration, can be a challenge. Any fastener that is not set square to the WRB surface, may go in misaligned and enlarge the penetration at the WRB surface, may tear the WRB or may not seal to the WRB, etc. is a potential water intrusion condition into the wall cavity. Fasteners that do not self-gasket to the WRB surface may allow water intrusion; smooth shank staples that miss substrate support framing are of particular concern. Fasteners that are not installed where they penetrate the substrate support framing or blocking (‘shiners’) may allow water intrusion into the wall cavity, even if they penetrate sheathing, which is not acceptable purchase for fasteners as defined in ASTM C1063. Shiner fasteners may be abandoned in place, and the fastener head domed with sealant to achieve a watertight condition, or where removed, the remnant hole sealed watertight. ASTM D1970 is the industry standard evaluation method for determining the self-sealability of fasteners through a waterproofing membrane. While ASTM D1970 is an informative test, it has limitations when used to evaluate stucco cladding fasteners in typically encountered conditions found in stucco cladding systems and is a reference resource but may not always be definitive in emulating real world stucco wall cladding system conditions. In particular, it applies to smooth shank nail fasteners not screws, installed only into plywood, with other particular conditions, into a roof surface not a wall, and other factors.
Embed lath accessory intersections, corners and terminations into dabs of sealant or caulking which minimizes long term UV exposure and hence degradation of the sealant or caulking. Avoid topical sealant application at lath accessories after the lath accessories are installed. Applying sealant or caulking topically after the lath accessory is installed is not optimum because it may be difficult or not possible at all to effectively seal the condition watertight, and exposure to UV allows degradation and requires maintenance, and exposed sealant may be an aesthetic issue.
Concerning water intrusion, a fundamental issue with stucco wall cladding systems where lath is fastened with nails, screws or staples through a WRB to a substrate support, is the multiple penetrations of lath fasteners through the WRB. Water finding its way behind the stucco wall cladding system has been known to intrude into the wall cavity around incorrectly installed fasteners, or when fasteners have been removed leaving an open hole in the WRB, or if the fasteners miss framing members and other vulnerable conditions in the WRB and flashing system. ASTM C926 recognizes that stucco wall claddings are not inherently watertight and requires sealant or caulking at exposed stucco wall cladding panel ends and edges to prevent the entry of bulk water from getting behind the stucco cladding. Other potential water penetration conditions through the stucco wall cladding include gaps created by shrinkage and thermal movements around perimeter casing beads, extruded aluminum terminations, intersections and terminations of SMJS, PMJS and BMJS and sometimes stucco crack conditions. Keeping the water out from behind the stucco cladding in the first place is a significant factor in assuring a functional and reliable stucco wall cladding system. The industry recognizes that stucco wall cladding is not a watertight system in and of itself and relies on the WRB, flashings and potentially a defined drainage cavity to manage and drain water that does make it past the stucco wall cladding system outer surface.
With regards to sealant or caulking for a stucco wall cladding system, determining which entity installs and is responsible for this sealant or caulking causes some consternation in the industry. One issue is that ASTM C926 requires sealant or caulking at certain stucco wall cladding perimeter conditions, yet sealant and caulking may be a separate trade from the plastering trade. Secondly, sealant or caulking may be required at certain conditions within the stucco cladding system yet ASTM C926 and C1063 are silent on these conditions. The solution to this sealant dilemma reflects a combination of the location of the sealant in question, contractual responsibilities, and the expectations and actual performance and workmanship quality of the stucco wall cladding system.
It is generally accepted within the industry that the stucco wall cladding craftsman is responsible for any sealant or caulking needed that is related to the installation of the stucco cladding system particularly at lath fastener penetrations of the WRB or repairing damage caused to the WRB resultant from installing the stucco wall cladding system over the WRB. Frequently the stucco wall cladding craftsman also installs the WRB at stucco conditions so it is appropriate that sealant at these conditions be within the stucco wall cladding craftsman’s customary scope of work. Likewise it is customary practice that any required sealant or caulking within the stucco wall cladding perimeter such as at BMJS, PMJS, and SMJS ends, intersections and terminations, sheet metal flashing laps, etc., is also within the purview of the stucco wall cladding contractor, where it is true that the stucco craftsman installs these components and subassemblies.
ASTM C926 directly recognizes the importance of sealant or caulking at the stucco wall cladding system perimeter (panel ends and edges) as an essential functional component for the stucco wall cladding system where it adjoins with dissimilar materials by specifying sealant or caulking at these conditions. ASTM C926 however, does not specify the entity responsible for installing sealant at stucco panel ends and edges. ASTM C926 is a reference specification, similar to contract specifications prepared following Construction Specifications Institute (CSI) specifications. Specifications in a project manual, whether they be Sections in a project manual or codified reference specifications as in ASTM Standard Specifications, specify a ‘unit of work’ – e.g. the work required, but not an identification of the specific entity responsible for executing the work, other than the contracting party of the general contractor.
The point is that any party can be contractually responsible for the sealant and caulking occurring at the perimeter of the stucco wall cladding system, a determination just needs to be agreed upon. One precedent for determining responsibility is realizing that perimeter sealant or caulking is an integral component of other non-stucco wall cladding exterior wall-related systems materials and their installers – e.g. metal panel cladding, windows, curtain walls, doors, plumbing and electrical penetrations, etc, so the same approach could be applied to the stucco wall cladding system. An issue with this approach is that most stucco craftsmen are not trained or experienced in the sealant joint trade and know their limitations and there may be trade boundaries or licensing issues. To provide the perimeter sealant joints, some projects will engage a separate dedicated sealant subcontractor for sealant work for the entire project other than where sealant or caulking occurs within separate individual systems. On other projects, for contracting convenience, warranty management and other reasons, sometimes general contractors will assign the sealant and caulking related to a given system to the relevant subcontractor. This is not generally an unreasonable practice it is simply a matter of contract. Where the stucco craftsman is required by contract to provide perimeter sealant, if not personally qualified or willing to self-perform the sealant or caulking work, and if allowable by trade and licensure laws, it is within their prerogative to subcontract for the sealant and caulking with qualified entities to comply with their contract.
The following images represent a few examples of some of the more common conditions that can allow bulk water intrusion into, around and through a stucco wall cladding system, and potentially into a wall cavity that require sealant or caulking or other effective repair method to maintain watertight integrity of the stucco wall cladding system. These examples are not a comprehensive list:
Empty holes through WRB at removed lath fasteners
Removed lath fastener through OSB sheathing between framing members.
Water testing in process without differential pressure.
Staple leg shiners allowing water intrusion
Testing in process without differential pressure
(Click photo to see video)
Staple leg shiner installed between framing members.
Gypsum sheathing does not effectively gasket fasteners
Water testing in process without differential pressure.
Lath fastener installed into framing member, but not drawn tight to WRB
Lath fasteners not in compression can allow water intrusion.
Water testing in process without differential pressure.
Staple leg shiners at 7/16 inch thick OSB sheathing
3/4 in. embedment into framing members
is not achieved as required by ASTM C1063
Lath fastener shiners in wood based sheathing can allow water intrusion
Photo courtesy of Paul Ellringer PE, CIH, www.airtamarack.com
Lath fastener shiners in cold climates can allow condensation
Photo courtesy of Paul Ellringer PE, CIH, www.airtamarack.com
A variety of solutions exist to address lath fastener-related conditions, depending on the circumstances. The following images generally illustrate potential solutions, although the list is not comprehensive:
Lath nails with furring wads, provides gasket to WRB
Sealant at lath fastener screw heads, provides gasket to WRB
Proprietary screws with sealant-filled
furring device provides gasket to WRB
(Photo courtesy of Greg Stephan of Fasten Seal Products LLC)
Unsealed lath accessory splice is a potential water path into the
wall cavity. Mock-up wall omits WRB for visualization purposes.
Water testing in process without differential pressure.
(Photo courtesy of www.RobertTellez.com of Roberts Consulting Group)
Unsealed lath accessory intersection
is a potential water path into the wall cavity
Unsealed BMJS subssembly intersection
is a potential water path into the wall cavity
Unsealed lath accessory termination is a
potential water path into the wall cavity
Embed lath accessory splices, intersections, terminations
into sealant, avoid topical sealant application
(photo courtesy Jim Gulde, Masonry Information Technologists, Inc.)
Sealant applied to intersection of window head Z-flashing (no end caps)
and top end of vertical window jamb casing bead
Sealant applied at intersection of EATS reveal
and vertical window jamb casing bead.
Sealant applied at intersection of Double-V Horizontal Drainage
screed and vertical window jamb casing bead
Sealant applied at intersection of vertical SMJS subssembly and
upper horizontal casing bead at stucco panel edge
Horizontal SMJS subssembly splice embedded in sealant bed
Horizontal SMJS subssembly terminations embedded in sealant bed
Sealant applied at lap splice of drainage screed,
Where placed over wall assembly below
Unsealed lowermost vertical lath accessory termination
at horizontal drainage screed to allow drainage
Stucco panel edge (without casing bead or sealant) at dissimilar
materials is a potential water path into the wall cavity
Arrow pointing to unsealed gap
Stucco panel edge (without casing bead or sealant) at dissimilar
materials is a potential water path into the wall cavity
Arrow buried into unsealed gap
Sealant filling separation gap between stucco panel edge casing bead
and window assembly (dissimilar material)
Gap and sealant between stucco panel edge sheet metal flashing
and pipe penetration (dissimilar material)
Disappearing joints: Sealant may also be used for exposed, decorative purposes. Stucco wall cladding system movement joints including BMJS, PMJS and SMJS are needed for functional reasons and they should be located wherever they need to be located for functional purposes to minimize stucco cracking – as the primary and foremost rationale. Because joints are visible at the stucco surface, they create narrow shadow lines that some, in certain situations, would prefer to not see, especially in common, perfectly planar, smooth stucco surfaces. ‘I don’t want to see joints – make them go away’ you say! The linear gaps at these subassemblies can be filled with a small backer rod and sealant to minimize the visibility of the joints, for decorative purposes if desired – and voila! – they disappear before your very eyes. Well almost disappear, and it can be pretty convincing especially if you squint - but you get the idea. The sealant should be pre-tinted to match the adjacent stucco color and not painted over, because painted sealant will crack due to joint movement. All the typical requirements for sealant apply – clean and prime the substrate, and correctly tool the sealant. Sand can even be embedded into the sealant to approximate the stucco finish texture and reduce sealant gloss if desired. The exposed sealant will not make the SMJS shadow lines completely disappear, but this approach will minimize their visibility.
Celebrate the joints: Alternatively, stucco wall cladding movement joints can also be used to express the function of the discrete panels and to visually segment and organize a building elevation. Imagine stucco cladding that looks like precast concrete or GFRC panels on that new commercial, institutional or luxury residential building in the downtown core. With careful attention to joint location, detailing, finish coat material and texture selection, stucco can be panelized to emulate precast concrete and GFRC wall claddings, both of which require sealant joints at panel perimeters. Precast concrete and GFRC are considered by some to be more desirable wall claddings than stucco, this is an opportunity for stucco to shine and recapture market share.
A consideration of this approach is that exposed sealant will eventually deteriorate and require periodic maintenance or replacement, but this is true of any exterior wall cladding system that includes sealant at joints – stone, precast concrete, GFRC, metal panels, etc. The difference is that these other claddings depend on sealant as a critical component of the cladding system that protects the building from water intrusion. With stucco, exposed sealant used for decorative purposes to fill movement joints is not a critical component of the stucco cladding system for avoiding water intrusion.
The use of more articulated, non-smooth surface, profiled textures is another approach also minimizing the visibility of stucco movement joints.
Color-matched, sealant-filled vertical SMJS pleats
over horizontal EATS channel
Color-matched, sealant-filled SMJS subssembly pleats
disappear almost completely
A great example of using color-matched, sealant-filled
SMJS subssembly pleats (top of photo), as compared to
non-sealant filled pleats (bottom of photo).
Weather exposed stucco panel edges, wall openings at windows, doors and penetrations, similar conditions, gaps at trims and certain lath fastener conditions may create water pathways that may allow water intrusion. Exterior stucco wall cladding systems at weather exposed surfaces require sealant or caulking, applied with reasonable care and concealed where possible, in strategic locations to keep bulk water out of the exterior stucco wall cladding system.
A single sealant material is typically used for both movement joints and non-moving conditions which are the primary materials for sealing potential water pathways for minimizing bulk water penetration into the exterior stucco wall cladding system. Silicone sealants generally provide the greatest movement capacity and long term serviceability, but other sealant materials are available.
Holes in the WRB are potential water pathways and must be sealed watertight
Shiners in the WRB are potential water pathways and must be sealed watertight
Gaps at weather-exposed trims are potential water pathways and must be sealed watertight
Gaps at stucco panel edges are potential water pathways and must be sealed watertight
Sealant used to conceal stucco movement joints is discretionary
Provide sealant or caulking, applied with reasonable care and concealed where possible, in strategic locations at weather exposed stucco panel edges, wall openings at windows, doors and penetrations, similar conditions, gaps at trims and certain lath fastener conditions to seal potential water pathways that may allow water penetration.
Specify and use a compatible, durable sealant material, with sufficient movement capability for both movement joints and non-moving conditions.
Stucco Minimum Standard of Care: Inspect 100% of the WRB during and after lath and lath accessories are installed for removed fastener holes and seal holes watertight.
Stucco Best Practice: Water test 100% of the WRB after lath and lath accessories are installed to locate obvious or potential water pathways to minimize water penetration.
Stucco Minimum Standard of Care: Inspect 100% of wall cavity surfaces for lath fastener shiners after lathing and lath accessories are completely installed. Remove loose shiners and seal holes at WRB watertight. Stable shiners that create a reliable compression condition with the WRB can be abandoned in place, but should be sealed at the WRB watertight, except in cold climates subject to condensation where shiners should be removed and the remnant hole sealed watertight.
Stucco Best Practice: Remove shiners and seal holes at the WRB watertight. Seal all lath fasteners at the WRB or specify and use proprietary lath fasteners that include an integral sealant.
Stucco Minimum Standard of Care:
· At lath accessory butt splice conditions, provide splice plates, end caps and prefabricated intersections that can be sealed watertight where available for lath accessory profiles.
· At weather-exposed surfaces, seal stucco movement joint (BMJS, PMJS, SMJS) and decorative joint splices, intersections, terminations watertight, to minimize bulk water penetration behind the stucco wall cladding system. Embed exposed lath accessory splices, intersections, terminations in a thick sealant daub to conceal the sealant as the lath accessories are installed. Avoid topical sealant application at lath accessories after the lath accessories are installed.
· Stucco Minimum Standard of Care: Seal lap splices of drainage screeds and flashings, where water penetration through the lap splice may allow water penetration into the wall cavity.
· Stucco Minimum Standard of Care: The ground facing end of vertically installed lath accessories should not be sealed when terminating into a horizontal drainage flashing weep screed or drainage Subssembly, to allow drainage.
Stucco Minimum Standard of Care:
· Avoid using the ‘integral stucco stop’ such as may be provided with window and door assemblies. Provide a casing bead, separation gaps and sealant over backer rod at stucco panel edges from the perimeter casing bead to adjacent dissimilar materials such as at window and door assemblies, vents, ducts, equipment and penetration, flashings at electrical boxes, etc.
· Follow ASTM C1193 requirements for sealant joints design and installation, which specifies the minimum dimension width for a sealant joint as ¼ in., with the caution that this is a difficult width sealant joint to install and provides minimal movement capability. Provide substrate surface preparation, backer rod and tooling for correct hourglass shape.
Stucco Best Practice: Provide 3/8 in. minimum dimension width or wider separation gaps for sealant joints.
To minimize the visual impact of exposed stucco movement joint subassemblies, consider filling them with sealant over backer rod for decorative purposes.
(1) ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
(2) ANSI A42.2-1971 Portland Cement and Portland Cement-Lime Plastering Exterior (Stucco) and Interior
(3) Technical Manual, Keene Corporation, Penn Metal Products, undated, c.1980
(4) Exterior Lath & Plaster Control Joints, Planned Points of Stress Relief, Western Conference of Lathing and Plastering Institutes, Inc.(WCLPI), undated, c.1980
(5) Minimum Property Standards, US Department of Housing and Urban Development (HUD), 1981
(6) Keene Corporation product catalog, 1983
(7) Guide Specifications for Metal Lathing and Furring, 920-91, Metal Lath/Steel Framing Association (ML/SFA Division of NAAMM), 1991
(8) Guide to Portland Cement Plastering, ACI 524R, American Concrete Institute, 1993
(9) Portland Cement Plaster (Stucco) Manual, EB049 Portland Cement Association, 1996
(10) Stucco Resource Guide, Northwest Wall Ceiling Bureau, 1997
(11) Stucco Resource Guide, Northwest Wall Ceiling Bureau, 1999
(12) Systems Manual, Texas Lathing and Plastering Contractors Association & the Texas Bureau for Lathing and Plastering, 2001
(13) Portland Cement Plaster (Stucco) Manual, EB049 Portland Cement Association, 2003
(14) Guide to Portland Cement Plastering, ACI 524R, American Concrete Institute, 2004
(15) Stucco in Residential Construction, Minnesota Lath and Plaster Bureau, 2007
(16) Guide to Portland Cement Plastering, ACI 524R, American Concrete Institute, 2008
(17) AMICO product catalog, 2009
(18) Guide Specifications for Metal Lathing and Furring, EMLA 920-09, 2009
(19) Lath Inspection Resource Manual, Second Edition, Minnesota Lath & Plaster Bureau, 2009
(20) Plaster Assemblies Manual Online, Technical Services Information Bureau (TSIB), 2011
(21) Fasteners and Self-Sealability of Weather-Resistive Barriers, RCI-TA-005-2014, Roof Consultants Institute Technical Advisory, 2014
(22) Plaster & Drywall Assemblies Manual, Walls and Ceiling Magazine, 2014
Consultation with licensed and experienced stucco professionals is recommended for stucco-related endeavors. No liability is accepted for any reason or circumstance, specifically including personal or professional negligence, consequential damages or third party claims, based on any legal theory, from the use, misuse or reliance upon information presented or in any way connected with StuccoMetrics.com.