Jeff Bowlsby CCS, CCCA
Exterior Wall and Stucco Consultant
Licensed California Architect
Stucco Best Practices
Each participant in the stucco industry should be diligent and proactive in their role to the team, to assure that the quality of stucco is as anticipated and intended - that it is durable, easily maintainable, meets reasonable expectations, has beauty, and minimizes the possibility of unsatisfactory service or litigation.
This webpage describes generally applicable suggested Stucco Best Practices - each would exceed a Minimum Stucco Industry Standard of Care. Reference other webpages on this website for additional suggested Stucco Best Practices.
Visit the StuccoMetrics Reference Archives webpage for cited references and further information.
Building owners, design professionals, stucco craftsmen and inspectors all desire optimum results from stucco – we generally all have the same goals and aspirations. No two stucco assemblies are identical; each varies in functionality, performance, durability, aesthetics, cost and in many other ways. Stucco can be assembled to satisfy minimalistic expectations only, or it can be a robust, creative wall cladding that is a buildings greatest asset. What stucco is to be, is determined by those who make the decisions that determine what stucco is for a given application.
There was a time when the design profession focused on creating the best technical and creative building solutions for their client owners, and stucco was the wall cladding material of choice. Stucco craftsmen likewise concentrated on installing stucco with the greatest skill, care and performed high levels of workmanship. Up into the 1980s history reflects that the design profession and craftsman trades were largely collegial and collaborative towards the goals of a project. In many ways that situation has not changed even today, at least in spirit, and stucco remains today as a cladding material of choice based on its many excellent aesthetic and functional characteristics.
Conscientious, dedicated, design professionals and craftsmen have the best intentions for stucco, are not nefarious and are still trying to provide the best quality stucco within their abilities, but sometimes mistakes made are simply human errors because we are subject to human limitations. At other times, mistakes are oversights, lack of knowledge, or subject to schedule, cost, material or product limitations.
Stucco is what we make it, no more and no less. We determine the role stucco is to satisfy and if stucco is to meet minimum requirements only or exceed them.
Not that many years ago stucco-related construction litigation and the fear of it, was the exception whereas nowadays, it is unfortunately, a more common recurrence and part of doing business for all in the stucco industry. Regarding stucco when used on common interest development projects, or in situations of inexperience, problems in design, problems arising from installation or application, or problems with materials, it has become prevalent. But the same is true for anything construction-related, not just singling out stucco.
A proliferating industry of construction defects experts has arisen and made an influence on the traditional owner-architect-contractor team relationships and project delivery process. Today’s expediency and cost sensitivity in the project delivery process can sometimes exacerbate this even further due to project time and budgetary pressures. These circumstances have not always been beneficial in the short or long terms to projects that include stucco, to project teams that design and install stucco or to owners of stucco clad buildings.
The awareness and sensitivity to stucco litigation has significantly influenced the decision making process during design and construction, both positively and negatively. It has sometimes encouraged the use of better quality control in design, materials and workmanship. There is no question that it has had a profound effect on the inter-professional trust and confidence amongst the design and construction communities in particular.
What is true in all cases though is that stucco has become exponentially more complex in the last few decades for design professionals, for product manufacturers, for craftsman and for inspectors. The expectations of building owners regarding stucco quality has increased.
Not that many years ago the built-up roofing industry faced similar issues. Roofing then was a site-constructed, generic system, made up of many different materials from several manufacturers. An architect then would specify every material and process of the roofing system and the contractors would build what amounted to a custom roof system for every installation. That condition led to an array of issues from design to workmanship to performance. Sound familiar? Nowadays, roofing is largely specified as a certain proprietary roof system by number, from a selected manufacturer, and craftsmen are required to be by manufacturer-trained and certified installers to preserve warranty provisions. Detailed manufacturer-provided publications and shop drawings describe every component and aspect of the system for the architect of record’s review and approval. Many roofing problems have diminished, and quality and durability has increased as a result. The stucco industry can learn from the roofing industry looking ahead.
Going forward by proactively working together, while there is no 100% certain method of assuring immunity from litigation, stucco design and construction professionals can minimize the risk of legal proceedings by taking a fresh look, and endeavoring to use careful, proactive, defensible approaches by each stakeholder in delivering stucco cladding to the marketplace.
If the stucco cladding system is designed and constructed to respect a reasonable standard of care and with attention to detail, it will have reasonable quality and performance, and if all conditions comply with or exceed Minimum Stucco Industry Standard requirements, then we can hopefully put the majority of stucco litigation behind us. Exceeding Minimum Stucco Industry Standards only helps all stucco to succeed.
Regardless of building type, building occupancy, geographic location or architectural style:
· Follow and comply with codified Minimum Stucco Industry Standards (building codes and ASTM etc.) in stucco design and construction as a minimum baseline requirement for all stucco wall cladding assemblies.
· Minimum Stucco Industry Standards of Care are suggested for convenient reference.
· Stucco Best Practices are suggested that exceed Minimum Stucco Industry Standards to provide enhanced stucco aesthetics, quality, durability and or performance.
· Carefully follow requirements of Minimum Stucco Industry Standards explicitly, or exceed them, and avoid shortcuts.
· Key persons and those supervising anyone less experienced involved with a stucco project, whether in ownership, design, construction or inspection roles, must thoroughly understand the project stucco-related construction documents and detailing, regulatory requirements including the building code and ASTM Minimum Stucco Industry Standards for products and installation as well as the specific stucco requirements for the project.
· Where gypsum panel sheathing is the substrate, design the gypsum panel sheathing control joint locations and installation detailing to comply with requirements of ASTM C1280 Application of Exterior Gypsum Sheathing Panel Products for Use as Sheathing.
· Water-Resistive Barrier (WRB) system: At building code defined weather-exposed surfaces provide a code compliant WRB system, and integrated flashings. Understand and implement the simple concept of a continuous WRB system, which includes flashings and sealant at wall openings and penetrations. Be vigilant to continuously integrate the WRB system with wall opening assemblies and penetrations, and provide redundant drainage provisions to eliminate water pathways into a building.
· Proprietary materials: Obtain and carefully follow product manufacturers written requirements, code evaluation reports and inspection requirements for each stucco product or material to the letter.
· All project team members must function as a collegial team and expect the same of their fellow team members. If a stucco product or material or detail or installation practice is questionable to any project team member, it should be brought to the attention of the architect for a coordinated resolution.
· Exceed Minimum Stucco Industry Standards requirements where allowed, whether they be a minimum code requirement, minimum manufacturer requirement or otherwise.
· Upgrade the quality of the WRB systems and flashings to be robust. Although concealed, it is the primary protection against water intrusion into the building.
· Create and maintain a project-specific stucco information folder for each project with copies of all stucco-related drawings, details, specifications, product data and installation requirements, code evaluation reports, communications, photos and other related documents for convenient use and field reference. The folder can be in hard copy or digital format, whichever is most convenient.
· Avoid generic (non-proprietary) stucco wall cladding systems over continuous insulation assemblies where the stucco is supported on cantilevered lath fasteners, where the stucco is in direct contact with the foam plastic insulation, and where the insulation is in the wet zone (outboard of the WRB). These conditions are more vulnerable to marginal stucco performance, have not been rigorously time tested, are labor intensive to assure quality, and more conventional assemblies are available to achieve the intended energy performance results. Where stucco over continuous insulation is necessary, select proprietary stucco wall cladding systems from those available in the market place which have code acceptance and a manufacturers backing.
· Avoid calcium chloride admixture accelerators, calcium aluminosulfate (CAS) or calcium sulfoaluminate (CSA), gypsum-based or lime-based stucco materials for exterior building use.
· Provide sufficient budget and schedule for time and cost to correctly design, install and perform quality control for the stucco cladding, including inspections, and corrections.
· Provide sufficient budget and schedule for time and cost to fully moist cure the stucco base coats, including provisions for temporary scaffold enclosures and supplemental heating or cooling where required.
· Determine appropriate expectations and requirements for the stucco cladding, and retain qualified and experienced design and construction team members. Stucco cladding as a primary wall cladding material is highly visible, makes the first impression and speaks volumes about the quality of a building, is expected to be of service for the life of the building, and stucco exterior weall claddings are fully capable of meeting those expectations. The acceptability, performance and quality of the stucco as it relates to owner expectations are largely related to the qualities and characteristics of the substrate, stucco materials, design detailing and workmanship. If the stucco is expected to be of high quality then a high quality substrate, stucco materials, design detailing and workmanship must be assured. All stucco is not the same.
· Traditionally, the architect will design the entire stucco wall cladding system, specify each of its materials and components, finishes and detail every condition in much the same way that the architect designs the casework, roofing systems, waterproofing, sheet metal flashings, etc. Not to mention the assumed liability with this approach, the architect must be knowledgeable and experienced in all aspects of stucco systems, from Minimum Stucco Industry Standards requirements to the benefits and limitations of individual stucco products and materials, and to make the most appropriate decisions regarding stucco for the specific project conditions. Minimum Stucco Industry Standards, products, and practices change regularly so there is a lot to be aware of and stucco system design is a lot to ask of any architect in the context of contemporary architectural practice. If the traditional design approach is used, avail yourself of every professional quality control means available to assure that the construction documents regarding stucco are complete, clear, comprehensive, correct, coordinated, and not self-conflicting.
· As applicable to either the traditional design/bid/build or design/build project delivery process, consider specifying the stucco cladding system or the entire exterior wall system as provided by a singular design/build entity that includes a specialized licensed design professional and specialized wall contractor. The stucco wall cladding design and delivery process can be handled effectively with stamped shop drawings and submittals. The stucco wall cladding system or complete exterior wall system including framing, interior and exterior finishes, even fenestrations may be provided under a single source responsibility, to maximize efficiencies, coordination, quality control and reduced costs. Specify performance expectations, inspections and field testing by independent third parties that provide for quality assurance.
· Avoid new stucco-related products or practices in the marketplace without a proven reputation of at least several if not 10 years minimum of market and installed performance history. The architect is sometimes confronted with new-to-the-market or new-to-the-architect, stucco products or practices - occasionally proven, sometimes not. The stucco industry has a storied history of products and practices being quickly developed and insufficiently tested before being brought to market. Installation instructions are sometimes not available or comprehensive for new or even long established stucco products and practices in the marketplace, a sure indication of products and practices to avoid or seek out better quality solutions.
· Design the stucco cladding to a higher level of quality than the Minimum Stucco Industry Standards require, complying with and surpassing the Minimum Stucco Standard of Care.
· Avoid designing open stud framing and avoid sheathing only selected locations of a building, and not sheathing other locations when under stucco, to avoid variations in stucco thickness, which cause stucco cracks. Design a uniformly aligned and continuously planar substrate within planar substrate tolerances which may require shims under sheathing or leveling compounds over sheathing to avoid excessive or abrupt thickness changes in the stucco cladding to avoid stucco performance issues.
· Design every exterior stucco clad surface. Often overlooked locations include roof facing surfaces of parapet and penthouse walls, interior and side column elevations of arcades, exterior soffits at building entries or corridors, projecting eave overhangs, exterior wall articulations (recesses) that conceal wall surfaces in traditional exterior elevation views and window recesses especially where lath accessories or finishes return into wall openings. If each surface is not depicted in the construction documents, require stucco shop drawings to depict each surface.
· Design every exterior stucco opening or penetration, and each stucco surface mounted equipment attachment, coordinated with the stucco system. Depict every outlet, louver, exhaust duct, hose bib, fire sprinkler, recessed lighting, surface mounted electrical disconnect etc., to coordinate stucco lath accessories and detailing. If each of these items is not depicted in the construction documents, require stucco shop drawings to depict each condition.
· Design a robust and continuous WRB system with flashings integrated in a watertight manner (sealed) to wall opening assemblies and penetrations.
· Design generous and redundant wall drainage and flashing provisions at each story height interval of multi-story buildings or more frequently, at ground facing, weather exposed soffit corners, and above wall openings.
· Specify high quality stucco basecoats with fiber additives and polymer admixtures, a reinforced polymer-modified cement or 100% acrylic lamina coat over the brown coat and finish coats and textures that conceal cracks and shed water.
· Design stucco repair requirements for scaffold tieback penetrations and lath fastener shiners, or design permanently exposed tieback provisions.
· Avoid designing casing beads as flashings because corner conditions and splices cannot easily be made watertight with casing beads. Require watertight, continuously flanged flashings at wall openings and penetrations.
· At each wall opening and penetration such as windows, doors and louvers, piping and electrical box penetrations, graphically depict a head and sill flashing with stucco perimeter grounds, integrated with the WRB regardless of whether or not the wall opening assembly or penetration item has an “integral stucco stop”. This is an often overlooked requirement of Minimum Stucco Industry Standards which when ignored, can contributes to unsealed separation gaps and cracking from stucco shrinkage movement and differential thermal movement effects between the stucco and dissimilar material components. Provide a sealant filled 3/8 in. wide gap between perimeter wall opening flashings or casing beads and the wall opening assembly or penetration to accommodate the differential movement and seal water out of the stucco cladding system.
· Graphically depict the complete spectrum of required stucco details, especially with an eye towards drainage flashings, planar transitions, lath accessory intersections, splices and terminations, sealants and their interface with adjacent construction and components.
· Avoid stucco cladding on weather-exposed low slope surfaces. Low slope is any surface less than 60 degrees from horizontal, typically surfaces such as parapet caps, balcony, stair railing and wall caps, and recessed window sills. Design sheet metal flashings (copings) over low-sloped waterproofing as the best technical solution in lieu of low slope stucco cladding. Stucco is not a roofing material; its surface collects dirt which can support organic growth. Problems such as how to resolve vertical wall joint subassemblies (BMJS, PMJS and SMJS) transitions where they intersect low slope conditions at parapet wall caps are difficult and usually not sufficiently resolved in the industry, and best avoided. Stucco wall caps tend to be long and narrow surfaces, SMJS and BMJS subassemblies are not appropriate to be located on these surfaces because the stucco easily cracks on these disproportional surfaces that may allow water intrusion into the wall system. Polymer finish coatings require significant slope and limited dimensional exposure and their durability is reduced on low slope surfaces. All finish coat materials on low slope surfaces collect dirt which may foster organic growth and discolored stucco.
· Carefully consider finish coat material and texture options from a design and serviceability perspective before selection and specification. Finish coats serve a decorative purpose only but they have a big impact on the perceived acceptability of the stucco, especially regarding crack visibility. Some will prefer the mottled coloring aesthetics of a pigmented cementitous finish, yet cementitous finish coats colors may fade, may effloresce and may not hide cracks well. Lighter colors, polymer admixtures and polymer finish coats minimize efflorescence and color variations. A polymer modified cement, or 100% acrylic, fabric reinforced lamina basecoat and polymer finish coat over the brown coat can dramatically reduce visible cracking. Coarsely textured finishes minimize crack visibility, and contribute to an architectural aesthetic, whereas cracks are magnified at smooth textured finishes. Also consider the aesthetic advantages and variety of embedded aggregates available as an alternative stucco finish. Light colored, medium to coarsely textured stucco finishes are suggested for general acceptability. A wide palette of stucco finish materials, colors and textures can be intermixed on any building for aesthetic effect.
· Eliminate ambiguous specification language such as: “Provide galvanized or solid zinc accessories.” Galvanized and solid zinc are different materials, and their installed costs and performance characteristics are significantly different. Solid zinc alloy lath accessories availability is not as widespread as galvanized and the material cost is different. If your specifications read this way you will get galvanized accessories because they are less expensive materials and less costly to install. That word “or” can be problematic if used carelessly. Create clear, definitive, declarative specifications without ambiguities.
· Carefully and completely specify finish coat material and texture specifications, which are frequently inadequate. A specification that only says “Provide factory prepared finish coat material to be selected by architect from manufacturer’s standard color” does not provide enough information to the contractor. This specification needs at least the type of finish coat material (cement, polymer, specialty) and preferably a basis of design product – manufacturer, product name and any particulars such as aggregate selection, color or special characteristic.
· Specify the finish coat texture with a photo of the required texture.
· Specify products requiring enhanced corrosion resistance for lath and exposed lath accessories/flashings as appropriate for the local environment. Stainless steel is probably not needed in desert climates, standard galvanized in coastal areas or around swimming pools can be problematic.
· Specify criteria for evaluating the stucco work for acceptability by specifying reasonable and achievable requirements. Specify measurable tolerances for acceptable finish planarity, efflorescence, crack width, crack location, crack visual density etc. Be aware of the effects of critical lighting during evaluation.
· Specify a stucco preconstruction conference to review and discuss the projects stucco requirements and to coordinate and resolve conflicts. Schedule the conference to occur only after submittals and shop drawings are reviewed and approved.
· During construction, regularly and carefully observe and document the progress of the stucco system work with periodic site visits, extensive photographs, including overall photos and close-ups of critical conditions. Distribute illustrated field reports to document progress and communicate any needed corrections.
· Design drainage screed flashings not only at the bottom of walls (foundation weep screeds), but also include ‘bottom of wall conditions’ occurring above upper floor balcony surfaces, at window heads, at base of stucco-clad chimney walls above roofs and other walls above roofs, as well as at weather-exposed, ground facing soffit corners.
· Provide horizontal drainage flashings or drainage screeds at weather-exposed surfaces of stucco clad buildings and at regular intervals on multistory buildings. Consider alignments with floor lines or window heads.
· Assure that stucco products are provided with comprehensive and definitive information on any limitations to the use and installation of the products and materials.
· Stucco materials, products and lath accessories do not function or exist in isolation; they create sub-assemblies with other stucco components. Design, construction and inspection authorities must have information available from manufacturers on the proper selection, use, installation and performance characteristics for their evaluation to assure they are commensurate with the project needs and expectations.
· Assure that all stucco products manufactured or distributed are capable of a minimum service life expectation of at least 10 years, or longer to match the service life of the building.
· Building codes and Minimum Stucco Industry Standards do not currently provide sufficient information for all stucco conditions, stucco materials, or lath accessory installation requirements. It may not be sufficient to simply reference ASTM C1063 or C926 for using products and materials. Where information voids exist, manufacturers should provide the required information along with the products and materials.
· Stucco lath accessory product manufacturers should provide comprehensive detailed sample generic installation diagrams, unique to each lath accessory that completely and accurately depicts all product physical and performance characteristics, required installation requirements, relationships to adjacent materials and material limitations. Many manufacturer-provided details are incomplete or incorrect in some way and do not provide design professionals, stucco craftsmen or inspectors with an appropriate level of detailed information needed for their effective use. Indicate all product dimensions, indicate framing/blocking requirements for required fasteners. Indicate acceptable fastener types, locations and spacing requirements. Indicate how the accessory integrates with the WRB and accommodates drainage. Indicate requirements for splicing, lapping, terminating, transitions at corners, and sealants. Indicate available lath accessories such as splice plates, end caps, spacers etc. For BMJ and SMJ lath accessories indicate the reasonable range of movement capabilities and performance limitations. If this information is not available, test for it and provide it. Provide substrate acceptability requirements and shimming parameters if shimming lath accessories is acceptable, or indicate that shimming is not acceptable. Indicate joinery conditions and requirements. Indicate specific requirements particular to horizontal lath accessories vs vertical lath accessories. Indicate where and how solid flanged vs expanded/perforated lath accessories should be used. Indicate requirements for the use of sealant with lath accessories.
· Thoroughly review and follow construction document requirements explicitly, without variation. If anything in the construction documents is not clear or conflicts with other requirements or does not meet Minimum Stucco Industry Standards, it is the stucco craftsman’s responsibility to inquire and bring these conditions and supporting documentation to the architects’ attention for resolution. Structural drawings do not trump architectural details, specifications do not trump plan notes, etc. The design authority traditionally, and often contractually, has the responsibility to review, coordinate and express the correct requirements, and to evaluate and resolve conflicts.
· Prepare, review and submit complete stucco submittals and shop drawings for approval as specified. Revise and resubmit if required, do not begin stucco work or convene the stucco preconstruction conference until stucco submittal and shop drawings approvals are received.
· Use the stucco preconstruction conference and regular communications such as RFI’s to review and discuss specific stucco requirements and to coordinate and resolve conflicts. Suggest preceding an RFI with a telephone conversation before preparing or submitting paperwork.
· Stucco can only be as good as its substrate. Before beginning the stucco work thoroughly inspect the substrate and verify that all substrate conditions are acceptable and meet Minimum Stucco Industry Standards. Inspect for a stable, dry substrate, planarity, plumb, and alignment of framing and sheathing, and for framing members/blocking required to install lath, lath accessories and required fasteners. Inspect substrate conditions in gypsum sheathing substrates for conformance with ASTM C1280 (notched panels at wall opening corners) and panel edge gaps in wood based sheathing substrates. Inspect wall openings and installed windows, doors and louvers, penetrations for required flashings. Reject any unacceptable substrate conditions and require corrections in writing if others are responsible for the substrate. The stucco work should not require extensive use of shims, if at all, or stucco thickness variations to accommodate substandard substrate conditions, because the stucco quality and performance will be marginalized.
· Rely on no other entity to be your inspector; the stucco craftsman is responsible for every condition of the stucco work, whether or not an inspector notices your mistakes. Continuously inspect the installation process and correct non-compliant work as it progresses.
· Include an acrylic admixture and fibers in every scratch and brown coat batch, obtain pre-approval from the design authority if it is not specified.
· Rigorously moist cure stucco base coats (scratch and brown) for 48 hours minimum, preferably longer, regardless of ambient temperature, humidity or wind conditions. Disregard typical qualifiers (below 70F, above 70%RH etc) sometimes used as a condition to determining if moist curing is necessary, always moist cure liberally as a standard practice. Document the moist cure process performed with reports and dated photographs for accountability.
· Cement hydration is a chemical process and without sufficient moisture, the stucco will not properly hydrate or cure. Stucco shrinkage occurs for nearly a year after application, the longer curing time duration before the finish coat is installed, the fewer cracks will occur and the better stucco will look and perform.
· Avoid over-fastening the lath and lath accessories. Fasten to framing members only and seal fastener heads to the WRB where they miss framing.
· Be informed about the specific technical stucco requirements of the work on the construction drawings and specifications, know the Minimum Stucco Industry Standards and reject non-conforming stucco work.
· Develop project specific checklists for each stucco installation, and maintain a checklist for each part of a project.
· Document job site stucco installation activities with regular detailed and overall photos and daily field reports. Regularly (daily or weekly) photograph compliant and non-compliant work and review results with the project team who can make timely corrections. In addition to stucco work photographs, take overall photographs of building stucco substrate surfaces, stucco material stockpiles, stucco staging areas, and stucco work areas, etc.
· Record site weather data for any period where stucco work is in progress including the afterhours conditions during curing time periods. Record ambient temperature, relative humidity, wind direction and speed, cloud cover, direct sun and precipitation. Consider using a jobsite weather station with recording capabilities to monitor ambient jobsite weather conditions.
· The design/build project delivery process brings special contractual requirements, coordination and scheduling challenges to the overall project and stucco design and installation. Avoid temptations to reduce the time required or quality of the stucco design, products used or the installation process from what is required on a traditional design/bid/build project, the technical requirements for stucco are the same, only the delivery process coordination is the primary difference. The owner’s expectations of the completed work are the same. The performance and accountability of each project team member to the quality of the stucco work is the same.
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.