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Executive Summary

Context

Observations

A Study of Stucco Crack Typologies

Wall Opening Cracks

WOC 01   Wall opening reentrant corner crack, omitted SMJS

WOC 02   Wall opening reentrant corner crack, omitted SMJS at corner, crack migrates to nearby penetration

WOC 03   Wall opening reentrant corner crack migrates to adjacent dead end EATS

WOC 04   Wall opening reentrant corner crack connecting two adjacent reentrant corners at non-square/rectangular (L-shape) stucco panel configuration, omitted SMJS

WOC 05   Wall opening reentrant corner crack, with SMJS

WOC 06   Wall opening reentrant corner radial cracks emanating from small wall opening

Soffit Cracks

SOFC 01 - Soffit reentrant corner crack, with SMJS

SOFC 02 - Soffit cracking at ceiling soffit, parallel to rib lath span direction

Field of Wall Cracks

FOWC 01 - Field of Wall parallel vertical cracking aligning with stud spacings

FOWC 02 - Field of Wall cracking perpendicular to length of narrow roof parapet wall panel, omitted SMJS

FOWC 03 - Field of Wall horizontal parallel linear cracking at wall surfaces

FOWC 04 - Penetration crack – lighting fixtures, guardrails, pipes, etc.

FOWC 05 – Field of Wall cracking at stucco thickness variations – lath line wires at open stud framing

FOWC 06 – Field of Wall cracking at stucco thickness variations related to wrinkly building paper

Planar Transition Cracks

PTC 01 - 3-plane intersection (innie), reentrant corner of primary wall plane, omitted SMJS

PTC 02 - 3-plane intersection (outie), reentrant corner of primary wall plane, onto adjacent recessed sill corner, omitted SMJS

Lath Accessory Cracks

LAC 01 - Perpendicular crack at SMJS lath accessory splice along stucco panel edge

LAC 02 - D-crack emanating from SMJS splice, at acute angle pie-corner panel geometry.

LAC 03 - D-crack emanating from single horizontal SMJS splice near panel corner.

LAC 04 - D-crack emanating from and connecting two SMJS splices near panel corner.

LAC 05 - D-crack at stucco panel corner, at arris condition

LAC 06 - Dead end SMJS termination crack

LAC 07 - Lath accessory profile transition crack, omitted SMJS

LAC 08 - Parallel crack at arris corner

LAC 09 - Parallel gaps along pointed ground lath accessory

Building Movement Cracks

BMC 01 - Building movement substrate support movement condition, omitted BMJS

BMC 02 - Building movement change in substrate condition, omitted BMJS

Discussion

Acceptable Stucco Cracking

Excessive Stucco Cracking

Stucco Crack Minimization Strategies

Stucco Crack Repair

Conclusions

Suggestions

GENERAL

PRODUCTS

INSTALLATION

Executive Summary

A study of stucco crack typologies, this webpage concentrates on the object and characteristics of the stucco crack itself.

Visible stucco crack phenomena are readily observable conditions.  Most people find stucco cracks objectionable based on visual aesthetics to one degree or another, and it is possible to reasonably minimize their occurrence with care in stucco cladding system design and craftsmanship.  They may represent normal stucco conditions and behavioral characteristics, they may be the result of insufficient stucco design or construction, or they may be the result of exposure to extreme service conditions.  Stucco cracks may or may not be the manifestation of concealed defects which may become discernable once the mechanisms that caused them are understood.

Visit the StuccoMetrics Reference Archives webpage for cited references and further information.

Context

Stucco cracks can be attributed to a number of various potential conditions and combinations of conditions.  It is well understood that some of the primary causes of stucco cracks include conditions and characteristics related to the following broad categories, this is not a comprehensive list:

·                     Stucco substrate support and movements

·                     Stucco lath and lath accessories materials and installation

·                     Stucco mix design and components

·                     Stucco system, assembly, subassembly and component design

·                     Stucco thickness variations

·                     Stucco curing

·                     Stucco shrinkage and thermal movements

·                     Stucco finish assemblies

·                     Stucco in-service environment conditions

As one of the traditional and primary approaches to stucco crack minimization, BMJS, SMJS and PMJS can be effective at minimizing stucco cracking.  This webpage concentrates on stucco movement joints as a primary crack minimizing method, but these are only one of several methods and considerations.

Shrinkage Movement Joint Subassemblies (SMJS) developed initially from the Perimeter Movement Joint Subassembly (PMJS), so a complete understanding of the principles and context presented on the PMJS webpage is fundamental to a foundational understanding of these subassemblies along with the additional information presented on this webpage.

Other stucco crack minimization methods concern themselves with the other bulleted topics above, which may be addressed elsewhere on this website now or in the future.

Observations

Stucco cracks are generally a manifestation of unmitigated stucco stresses.  Many factors contribute and combine to cause stresses resulting in stucco cracks.  Careful observation and evaluation of stucco crack patterns reveals a common repetitive typology of cracks and vocabulary of consistent crack characteristics and conditions.  The following examples of stucco crack patterns are an indication of generally occurring, often predictable and therefore potentially avoidable stucco crack patterns.  This webpage resource may be useful as a general guide only, it should not be considered as comprehensive or absolute, and does not purport to suggest absolute or guaranteed mitigation for avoiding all stucco cracks.

Stucco movement joint lath accessories and SMJS, PMJS and BMJS were developed to minimize stucco cracking caused by initial stucco shrinkage, thermal movements, and building substrate support movements.  All stucco movement joint subassemblies require discontinuous lath and other requirements to function correctly and to minimize stucco cracking.

A Study of Stucco Crack Typologies:  Unmitigated stress concentration conditions manifesting as stucco cracking, with commentary on Minimum Stucco Standards of Care and Stucco Best Practices.

Wall Opening Cracks

Wall Opening Crack WOC 01:  Wall opening reentrant corner crack, omitted SMJS.  The most common stucco crack condition.

·                Stucco Best Practice:  Avoid reentrant corners at stucco panels.  Locate SMJS at wall opening reentrant corners.

Wall Opening Crack WOC 02:  Wall opening reentrant corner crack, omitted SMJS at corner, crack migrates to nearby penetration.

·                Stucco Best Practice:  Locate SMJS at reentrant wall opening corners, provide lath patch reinforcement at wall penetrations.

Wall Opening Crack WOC 03:  Wall opening reentrant corner crack migrates to adjacent dead end EATS

·                 Stucco Best Practice:  Locate SMJS at reentrant wall opening corner.  Avoid dead end EATS and lath accessories.

Wall Opening Crack WOC 04:  Wall opening reentrant corner crack connecting two adjacent reentrant corners at non-square/rectangular (L-shape) stucco panel configuration, omitted SMJS.

·                 Stucco Best Practice:  Avoid non-square, non-rectangular stucco panel configurations (L-shape, C-shape, donut shape) to avoid reentrant wall opening corners.  Locate SMJS between adjacent reentrant wall opening corners to create square or rectangular stucco panel configurations.

Wall Opening Crack WOC 05:  Wall opening reentrant corner crack, with SMJS.

·                Minimum Stucco Standard of Care:  Assure correct SMJS installation with discontinuous lath for maximum SMJS movement.

Wall Opening Crack WOC 06:  Wall opening reentrant corner radial cracks emanating from small wall opening

·                 Stucco Best Practice:  Either locate SMJS at each reentrant corner, or specify lath reinforcement patch.

Soffit Cracks

Soffit Crack SOFC 01:  Soffit reentrant corner crack, with SMJS.  Even small reentrant corner conditions may propagate cracking. 

·                Stucco Best Practice:  Avoid reentrant corner condition at stucco panels.  Locate SMJS at reentrant corners and avoid non-square, non-rectangular stucco panel configurations.

Soffit Crack SOFC 02:  Soffit cracking at ceiling soffit, parallel to rib lath span direction.

·                Stucco Best Practice:  Avoid using rib lath at ceilings/soffits due to its inherent capability of creating stucco thickness variations which often result in linear, parallel cracking.  Require ceiling/soffit joists at 16 in OC maximum spacing, use 3.4 expanded metal lath, V-Groove.

Field of Wall Cracks

Field of Wall Crack FOWC 01:  Field of Wall parallel vertical cracking aligning with stud spacings.

·                 Stucco Best Practice:  Avoid stucco on open stud framing without sheathing to avoid stucco thickness variations that often result in cracking.

Field of Wall Crack FOWC 02:  Field of Wall cracking perpendicular to length of narrow stucco clad wall panels such as parapet walls, and omitted SMJS.  Panels between cracking occur in small square to rectangular proportions.

·                Stucco Best Practice:  Locate SMJS to create stucco panel areas of 1:1.5 geometry maximum

Field of Wall Crack FOWC 03:  Field of Wall horizontal parallel linear cracking at wall surfaces. This may be a workmanship issue related to ungapped sheathing panels, or paperbacked lath with integral line wires on open stud framing (omitted sheathing) or other condition.

·                Minimum Stucco Standard of Care:  Provide 1/8 in. gaps at wood-based sheathing panel edges. 

·                Stucco Best Practice:  Avoid stucco cladding on open stud framing without sheathing and use of paperbacked lath with integral line wires.

Field of Wall Crack FOWC 04:  Penetration crack – lighting fixtures, guardrails, pipes, etc.

Field of Wall Crack FOWC 04A:  Penetration crack – lighting fixtures, guardrails, pipes, etc.

·                 Stucco Best Practice:  At penetrations such as lighting fixtures, pipes/conduits, dryer vents provide lath patch on the diagonal, over the primary wall lath for additional reinforcement against localized cracking.  Provide isolation collar (flashing) with sealant filled gap at penetrations to accommodate localized shrinkage movement and differential movement with penetrating item.

Field of Wall Crack FOWC 05:  Field of Wall cracking at stucco thickness variations – lath line wires at open stud framing.

·                 Stucco Best Practice:  Avoid open stud framing and use of paper backed lath with line wires.

Field of Wall Crack FOWC 06:  Field of Wall cracking at stucco thickness variations related to wrinkly building paper

·                Minimum Stucco Standard of Care:  Provide SMJS correctly installed with discontinuous lath, small panel sizes and other methods of minimizing stucco cracking.

Planar Transition Cracks

Planar Transition Crack PTC 01:  3-plane intersection (outie), reentrant corner of primary wall plane, omitted SMJS.

·                 Stucco Best Practice:  Locate SMJS on primary wall at reentrant corner of 3-plane intersection and provide Double-V Internal Corner SMJS at adjacent interior corners.

Planar Transition Crack PTC 02:  3-plane intersection (innie), reentrant corner of primary wall plane, onto adjacent recessed sill corner, omitted SMJS.  This crack may also be related to a sheathing panel edge incorrectly located to align with wall opening corner.

·                 Minimum Stucco Standard of Care:  Assure sheathing panel joints are offset from corner (4 in minimum per ASTM C1280), and if of wood-based panel sheathing, the panel edges are gapped 1/8 in.

·                 Stucco Best Practice:  Provide SMJS aligning with wall opening reentrant corner on primary wall plane and provide Double-V Internal Corner SMJS at adjacent interior corner.

Lath Accessory Cracks

Lath Accessory Crack LAC 01:  Perpendicular crack at SMJS lath accessory component splice (butt splice) along stucco panel edge.

·                 Stucco Best Practice:  Avoid locating lath accessory splices along stucco panel edges, terminate only at intersections with other lath accessories.

Lath Accessory Crack LAC 02:  D-crack emanating from SMJS splice, at acute angle pie-corner panel geometry.

·                 Stucco Best Practice:  Avoid pie-corner stucco panel geometry.  Avoid lath accessory butt splices along panel edges, terminate lath accessories only at intersections with other lath accessories.

Lath Accessory Crack LAC 03:  D-crack emanating from single horizontal SMJS splice near panel corner.

·                 Stucco Best Practice:  Avoid butt splices of lath accessories along panel edges, locate lath accessory splices only at intersections with other lath accessories, not along panel edges.

Lath Accessory Crack LAC 04:  D-crack emanating from and connecting two SMJS splices (butt splices) near panel corner.

·                 Stucco Best Practice:  Avoid lath accessory butt splices along panel edges, locate lath accessory splices only at intersections with other lath accessories, not along stucco panel edges.

Lath Accessory Crack LAC 05:  D-crack at stucco panel corner, at arris condition.

·                 Minimum Stucco Standard of Care:  Assure correct SMJS installation with discontinuous lath for maximum SMJS movement.

·                Stucco Best Practice:  Locate SMJS to create panel areas of 1:1.5 geometry maximum

Lath Accessory Crack LAC 06:  Dead end SMJS termination crack

·                Stucco Best Practice:  Avoid dead end SMJS, terminate SMJS at intersections with other lath accessories.

Lath Accessory Crack LAC 07:  Lath accessory profile transition crack, omitted SMJS.

·                 Stucco Best Practice:  Locate SMJS at lath accessory profile changes, do not transition lath accessories along stucco panel edges.

Lath Accessory Crack LAC 08:  Parallel crack at arris corner.

·                 Minimum Stucco Standard of Care:  Assure lath continues around corner 1 stud bay minimum and that external corner reinforcement is packed solid with stucco.

Lath Accessory Crack LAC 09:  Parallel gaps along pointed ground lath accessory (SMJS lath accessory).  A gap can form at each side of a pointed screed as stucco shrinkage and thermal movement occurs.

Lath Accessory Crack LAC 09A:  Parallel gaps along pointed ground lath accessory (SMJS lath accessory).  A gap can form at each side of a pointed screed as stucco shrinkage and thermal movement occurs.

·                 Stucco Best Practice:  Avoid pointed ground (Single-V or Double-V) lath accessories; provide Single-J or Double-J lath accessories with capture flange.

Building Movement Cracks

Building Movement Crack BMC 01:  Building movement substrate support movement condition, omitted BMJS.

·                Minimum Stucco Standard of Care:  Locate BMJS at substrate support movement locations.

Building Movement Crack BMC 02:  Building movement change in substrate condition, omitted BMJS.

·                Minimum Stucco Standard of Care:  Locate BMJS at change in substrate material.

Discussion

Like death and taxes, everyone knows and acknowledges that stucco cracks.  It’s frequently the only conclusion – sometimes framed as the answer to a mystery when discussing why stucco cracks.  “Why do stucco cracks occur?  Because stucco cracks!”, when it really should be the response of last resort, and when nothing else can explain the crack phenomena.  The postulation here is that as a generality, cracks occur for a rational reason or combination of reasons; we just need to understand the reasons better and do what is appropriate to minimize the likelihood they will occur, or otherwise accept the results.  If we can get to the place where we better understand the conditions and characteristics or mechanisms that cause stucco cracks, we may be able to get to the place where we can greatly diminish their occurrence and frequency.

Stucco cracking at reentrant wall opening corners has been the single-most pervasive stucco crack condition and typology since portland cement-based plaster was first used as an exterior wall cladding on buildings over a century ago, including through today.  The combination of reentrant wall opening corners such as at windows, doors and similar wall opening conditions, and the stucco cracks that propagate from them are a fundamental and significant issue for the design authority and construction authority of exterior stucco wall cladding system to be cognizant of and to address.  Stucco cracks at reentrant wall opening corners can generally be minimized and potentially avoided with attention to detail in both the design and construction of stucco wall cladding systems.

Discussions of stucco cracking must consider the characteristics of the entire stucco system – the substrate support, WRB, lath and fasteners, lath accessories, base coats, all materials and workmanship, the finish assembly, texture and service and lighting conditions.   Stucco finish assemblies and textures have an important function in the stucco system for crack mitigation, where higher performance finishes and more articulated textures may help mitigate cracking better than brittle, low performance smooth surface finishes.  No studies have been performed or published information available by any entity as yet, to quantify what the mitigating effects of higher performance finishes or more articulated textures are, so as we discuss cracking generically, we can only presume the discussion to be in the context of minimum quality stucco systems – such as those that include cement finish coats, with integral color or painted, and a flat, planar, sand float texture.

Acceptable Stucco Cracking

Most rationale people agree that stucco cracking is an eyesore, but do circumstances exist where a stucco crack might be considered by some to be marginally acceptable?  A research paper I authored and which was published in 2010 by RCI, Cement Plaster Metrics:  Quantifying Stucco Shrinkage and Other Movements; Crack Acceptability Criteria for Evaluating Stucco, explored this question.  The conclusion was that the answer has two parts – a rational component and a subjective component.

As a practical matter, a stucco crack should not be acceptable if it has a role related to water intrusion that causes visible or concealed damage.  Some cracks penetrate the full thickness of the stucco membrane and can function as direct water pathways leading to the concealed WRB or substrate support.  Not all cracks are water pathways that result in concealed damage.  Stucco wall cladding systems are typically constructed in multiple layers of portland cement-based plaster, where outer coats can conceal cracks at underlying coats.  Proprietary stucco offered by certain manufacturers may consist of only a single coat of portland cement-based plaster.  Three-coat stucco typically has scratch, brown and finish coats by design as a characteristic of that system, which is a matter of good practice, and by its multiple layers adds redundancy.  Stucco Best Practices include additional layers such as a fabric-reinforced lamina basecoat or thicker finish coats which exceed minimum requirements.  An important functional reason for this is that a crack forming in an underlying coat is often covered and may not translate into or through subsequent coats to the stucco surface.  Cracks in the scratch coat can be concealed by the brown coat, and brown coat cracks can be concealed by the finish coat, etc.  A stucco cladding system with a greater number of plaster coats will likely have less visible cracking at the finish coat surface than a stucco cladding system with fewer coats.  Is a crack that one cannot see in a concealed layer, a problem either functionally or aesthetically?  The answer should be obvious to a reasonable person.

·                 Acceptable stucco cracking:  The stucco cladding system correctly complies with all required crack minimizing provisions so that cracking within the stucco cladding system could be qualified as acceptable.  BMJS, PMJS and SMJS are correctly installed and located, portland cement-based plaster is correctly proportioned, installed and cured, substrate support conditions are correct…in other words no condition is incorrect.  This circumstance is the condition where the phrase ‘acceptable stucco cracking’ is appropriate.  Minimum Stucco Industry Standards are just that – minimums, not Stucco Best Practices.   Some degree of ‘less than perfect’ should be acceptable when minimum standards are followed.

Beyond that, stucco crack acceptability can and should be evaluated based on a range of visible aesthetic priorities and subjective criteria of the beholder.  It is not likely that any two people will agree on the acceptability of any single crack, so ultimately a neutral person with authority just needs to make a well-considered determination.  The crack location, crack width, crack depth, crack visual density (visible cracking within a specific area), stucco finish color, texture and material, lighting conditions when observed – all these and more effect the acceptability of stucco cracking to individual persons.  That being said, based on my 2010 paper Crack Acceptability Criteria for Evaluating Stucco, the current general consensus in the industry, all sourced considered, is that a crack not exceeding 30-mils in width and narrower, may be conditionally acceptable in certain circumstances.  Cracks narrower than 30-mils wide in a smooth texture finish may not be acceptable to some.  A 30-mil wide crack and narrower, may not be very noticeable under certain conditions, and may be repairable with high performance finish coatings if the aesthetic of the coating is acceptable, which may not always be the case.  A crack located at the building entry at eye level may be objectionable to everyone, whereas the same crack on the third floor rear wall of a building may not be as much of a concern aesthetically because it is difficult to visually access.  A series of adjacent cracks less than 30-mils wide may be objectionable on the basis of visual density.

Excessive Stucco Cracking

When can stucco cracking reasonably be categorized as excessive stucco cracking?  Some will suggest that any stucco crack is an excessive crack.  At the other extreme others will pretty much shrug off any type or amount of cracking as a normal condition… “all stucco cracks” they say as if that cliché is a hall pass to trivialize any issues and justify the acceptability of any and all cracking.  If any single crack or group of cracks does not have a role related to water intrusion, then the condition is probably not a functional concern in terms of keeping the building water tight.  Excessive stucco cracking then becomes an aesthetic condition only.  A few resources have attempted to define excessive stucco cracking in largely subjective terms.   They suggest a certain number of lineal feet of cracking of a certain maximum width per square foot of stucco or words to the effect that excessive cracking means visually objectionable – but those criteria are not easy to define where everyone will agree.  Those approaches are non-starters because they are difficult to quantify and subjective at best.

A method for defining excessive cracking that can be considered is to use a rational evaluation process which is non-subjective.  One condition for stucco cracks to be considered as acceptable is the condition when stucco cracking occurs, in spite of the fact that all required measures to minimize cracking are correctly implemented.  Excessive cracking would be just the opposite.  Excessive cracking is stucco cracking that develops when all required or specified measures to minimize cracking are not implemented or not correctly implemented.  ‘Required’ means required by building code requirements which reference Minimum Stucco Industry Standards, or as specified requirements in contract documents.  This approach allows a variability in evaluating “acceptable” and “excessive” cracking conditions, based on the qualities and characteristics of the specified stucco wall cladding system, which is appropriate and determined based on the qualities and characteristics of the specific requirements of a given stucco wall cladding system.  It is generally reasonable to expect that a minimum quality stucco wall cladding system will perform to a lower standard (i.e. crack more) than a higher quality stucco wall cladding system (i.e crack less).

·                 Excessive stucco cracking:   The stucco application is not fully compliant with all required crack minimizing provisions, so the stucco cladding system or any portion of it could be justifiably categorized as excessively cracked.  Any number of issues could describe this condition – oversized stucco panel areas, incorrectly located or installed BMJS, PMJS or SMJS, incomplete curing, over fastening the lath, omission of specified fibers, incorrect substrate conditions, etc.

Stucco Crack Minimization Strategies

As a baseline, essential methods and approaches to minimizing cracks are described and required in the building code and Minimum Stucco Industry Standards.  These include a number of items many take for granted such as correct substrate preparation, 2 layers WRB, the specification and correct use of materials with certain characteristics – cement, aggregate, and water, effective workmanship, effective moist curing, etc.  Minimum Stucco Industry Standards also require the effective use of stucco movement joint assemblies and subassemblies correctly located and configured, with no exclusions.  Excessive cracking can occur if one or more of these potential maladies is overlooked or omitted.

The essential purpose for BMJS, PMJS and SMJS is to minimize the potential for stucco cracking by minimizing the transference of movements into and through the stucco cladding system, and releasing the induced stresses that manifest as stucco cracking at the stucco surface.  That can be a tall order and complicating matters, BMJS, PMJS and SMJS are imperfect subassemblies.

BMJS isolate the stucco wall cladding system from substrate support movements, and are located as the buildings substrate support requires.  A BMJS minimizes stucco cracking caused by building substrate support movement by physically isolating the edges of separate, adjacent building substrate support sections and their associated stucco wall cladding panels from each other.  The lath and substrate support are discontinuous at BMJS.  Visit the BMJS subassembly webpage for more information.

PMJS isolate the stucco wall cladding system from substrate support movements, and are located at perimeter conditions such as where columns penetrate through stucco soffits or where substrate support materials or conditions change.  A PMJS minimizes stucco cracking caused by perimeter building substrate support movement by physically isolating the edges of separate, adjacent perimeter building substrate support sections and their associated stucco wall cladding panels from each other.  The lath and substrate support are discontinuous at PMJS.  Visit the PMJS subassembly webpage for more information.

SMJS isolate adjacent stucco panels from each other, providing a location for shrinkage and thermal forces to accumulate, to minimize the possibility of stucco cracking.  While the substrate support is continuous through the SMJS because the SMJS is only concerned with stucco shrinkage and thermal movements and not substrate support movements, the lath is discontinuous at SMJS.  Visit the SMJS subassembly webpage for more information.

Other crack minimization strategies include enhancing the system, adding redundancies, higher quality materials and workmanship.  Fiber additives and polymer admixtures in basecoats minimize cracking.  More rigorous moist curing minimizes cracking.  Continuous fabric-reinforced lamina basecoats, closer spacing and strategic location of movement joints minimize cracking as do more flexible finish coats and more articulated textures.  The positive effects of these and other approaches to minimizing stucco cracking are recognized, but their exact level of enhancement is not known or quantified.  To achieve the highest quality stucco with the fewest cracks, consider including as many of these enhanced approaches for minimizing cracking.

Stucco Crack Repair

Should crack repairs be contemplated, effective repair method options are limited. The important characteristics of a specific crack require evaluation including whether the crack is static or dynamic, its causation, relationship to water leakage, location, width, length, relationship to adjacent cracks and building components, and other factors must all be considered before deciding on the need for and requirements to repair the crack.

Some cracks that are not otherwise aesthetically objectionable may best be left unrepaired to minimize the aesthetic impacts of repairs.  Painting alone may be a sufficient repair for the smallest of static cracks, if painting is appropriate for the specific stucco assembly.

Other cracks will be determined to require more elaborate repairs.  One proven effective solution overlays a complete, new continuous fabric reinforced base coat and finish coat over the entire affected panel(s), between panel joints, corners and perimeters.

Absent a new finish coat, attempts to make localized spot repairs may not be aesthetically acceptable as a result of challenges in matching or blending with the existing finish coat color or texture.  These methods include combinations of painting, routing out the crack and installing sealant, rubbing in patching compound, and spot repairs.

Crack Repair:  Crack routed, sealant installed, then painted

Crack Repair:  Crack not routed, patching compound rubbed into crack, then painted

Crack R­­­epair:  Pigmented cement finish, spot patched

Conclusions

The stucco crack typologies illustrated depict stress concentration locations and conditions that have manifested as stucco cracking, which serve to inform us of typical conditions where BMJS, PMJS and SMJS should be located, and how they should be configured for optimum performance.  The purpose of this stucco crack typology study is to begin to catalog consistent and recurring stucco crack phenomena, in hopes of understanding stucco cracks better and ultimately to eliminate them from the stucco dialogue.

We as stucco designers, craftsman and regulators should use the available materials and methods and do whatever it takes to avoid and mitigate excessive stucco cracking by using precaution in stucco cladding design and construction.  The default phrase “all stucco cracks” as used to justify every crack is clearly overused, unreasonable and not always rationally justifiable.  As an industry we have the knowledge, technology and capabilities to minimize the likelihood of most stucco cracks.  Let us be encouraged to provide robustly designed and constructed exterior stucco wall cladding systems with conditions conducive to avoiding cracking.  Every condition and component of the stucco wall system from its substrate support condition to its finish coat and texture must be evaluated and selected to minimize and avoid stucco cracks.

The term ‘acceptable stucco cracking’ can be mostly rationalized but has components that are subjective, whereas the term ‘excessive stucco cracking’ can be fully-based on a rational evaluation.

Localized crack repairs present challenges and the most effective repairs apply a new finish coat system over an entire panel surface.

Suggestions

GENERAL

Minimum Stucco Standard of Care:

·                 Comply with the ASTM C926 requirement for the design authority to determine and depict BMJS, PMJS and SMJS type, location, depth, and method of installation in the project contract documents.

Stucco Best Practices:

·                 Follow suggestions for BMJS, PMJS and SMJS indicated on their respective StuccoMetrics.com webpages.

·                 Carefully review and consider the relationships of common stucco cracking patterns and typology to building substrate support, stucco shrinkage and thermal movement stress concentrations.  Recognize the conditions and locations that cause stucco cracking to occur, and take precautions to avoid or minimize stucco cracking.

·                 Provide BMJS, PMJS and SMJS in strategic, stress concentration locations, that function to minimize stress concentrations within the stucco cladding s, and that define stucco panel areas and proportions more conservatively than current Minimum Stucco Industry Standards require.

·                 Recognize that by definition, BMJS, PMJS, drainage screeds, and casing beads, create one or more stucco panel area edges, terminations if you will, because lath does not continue through, but terminates at them.  These are literally, functionally and therefore effectively one-half of an SMJS because shrinkage and thermal movement can occur at them.

·                 At small dimension penetrations such as piping, electrical boxes, provide an isolation flashing collar with an annular gap filled with sealant over backer rod to accommodate localized movements at the penetration isolated from the stucco cladding, and an additional lath reinforcement patch over the primary lath.  This lath reinforcement patch should be a large aperture lath such as welded wire lath to allow excellent plaster embedment with the primary lath, and be installed on the diagonal, extending beyond the penetration by 6 inches minimum, and be wire tied to the primary lath layer to avoid lath fasteners that would otherwise miss framing.

·                 Implement some or all stucco crack minimizing methods, materials and proprietary enhancements to minimize stucco cracking.

PRODUCTS

Stucco Best Practices:

·                 Avoid pointed ground V or Double-V lath accessories to avoid the parallel gap that may allow water intrusion behind the stucco, unless they are horizontal drainage screeds that are intended to allow drainage from the gap that will occur between the edge of the screed and the stucco.

INSTALLATION

Minimum Stucco Standards of Care:

·                Comply with ASTM C1063 requirements for BMJS, PMJS and SMJS installation requirements

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.