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Sto Stucco Restoration and Crack Repair Specification R 300


1.01   Summary

A.         The general conditions, supplementary conditions and general requirements of these construction
            documents apply to the general contractor, subcontractors, material suppliers and all persons
            furnishing labor and materials under this section.

B.         Section Includes: description of requirements for materials and installation of stucco repair system
            as shown on drawings and as specified herein to complete work.

1.02  Description

A.         Design Requirements:  the structural wall system to which the stucco repair system is attached shall
            meet L/360 maximum allowable deflection criteria and applicable building code requirements.

1.03  Submittals

A.         Submit copies of manufacturer’s specifications, installation instructions and product data.

B.         Submit copy of applicator’s certificate of training, where training is required by manufacturer or
            product specifications.

C.         Submit samples for approval as directed by architect.

D.         Submit copy of manufacturer’s warranty.

1.04  Delivery, Storage and Handling

A.         All coating materials shall be delivered in their original sealed container bearing manufacturer’s name
            and identification of product with written application instructions and appropriate health, hazard and
            safety data.

B.         All ready-mixed coating materials shall be protected from extreme heat, sun and frost.  Factory      proportioned bagged materials shall be stored inside, off the ground in a dry area and protected  from

1.05   Job Conditions

A.         All materials shall never be applied if ambient and surface temperatures cannot be kept above
            38 degrees F during application and drying period.  For installation in temperatures less than
            30 degrees F supplementary heat shall be provided.  The installed materials shall be protected from
            exposure to rain and freezing until dry.


2.01   Material-General

A.         Manufacturer’s:  materials are specified by brand names to establish a standard quality, or by performance
            requirements and general description of the product.  The architect will consider substitutions for brand        names of  products specified, provided the procedures set forth for substitutions are followed.  The      architect reserves the right to reject any material which, in his or her opinion, will not produce the quality              of work specified herein.

B.         The following are acceptable manufacturers:

            STO CORP.

2.02   Surface Preparation
A.         Conditioners
1.         Sto Plex W - a ready-mixed water based surface conditioner with minimum solids content of  8% for
            treatment of dry, porous stucco/plaster  surfaces and load bearing painted surfaces.

2.         Sto Bonding Agent - a water based resin dispersion designed as a surface preparation for dry/porous
            concrete, masonry or stucco surfaces.  Also serves as an additive to Sto One Coat Stucco.


2.03 Patching, Leveling and Resurfacing

A.         Sto Leveler - a one component factory proportioned polymer modified fiber reinforced cement based
            leveler with water repellent additive for pre-filling surface cracks up to 1/4 inch wide and for leveling,
            patching or filling surface irregularities up to 1/2 inch deep in one application.

2.04   Waterproofing

A.         Sto Flexyl - a 100% acrylic copolymer based waterproofed for use with Portland cement and Sto Mesh
            to waterproof parapets, sloped sills and other areas that require a waterproof membrane to prevent
            water intrusion.

2.05   Crack Repair Materials

A.         Sto Flexjoint Compound - a ready-mixed elastomeric acrylic dispersion based joint compound and
            ground coat for filling surface cracks up to 1/8 inch wide and for use as a ground coat with Sto LPA Mesh
            to reinforce surface cracks up to 1/16 inch wide.

B.         Sto Flexyl - a 100% acrylic copolymer based waterproofer and stucco crack repair for use with Portland
            cement and Sto Mesh to fill and reinforce surface cracks up to 1/16 inch wide.


3.   Elastomeric paints:

A.         StoSilco Lastic - a silicone emulsion elastomeric flat paint for concrete, masonry, plaster or existing          acrylic based textured finishes; for brush, roller or spray application.  Minimum solids content shall be               60%.  Dry mil thickness shall be 15-17 mils in two applications (prime coat and finish coat).

Note:  Type, texture and color of paint shall be as indicated  on architectural drawings or per approved sample 
           submittal.  Color shall be identified in accordance with the Sto Color System and color fastness shall be a
           minimum of 8.  Lightness value shall be 30% or greater for Sto silicone based finishes.

2.06   Reinforcement

A.         Sto Detail Mesh - a symmetrical, interlaced glass fiber made from twisted multi-ended strands, and coated    to be compatible with Sto repair materials.

B.         Sto Mesh - a symmetrical, interlaced glass fiber made from twisted multi-end strands and alkaline
            resistant coating, at least 20 grams per square yard, for computability with Sto materials.  The mesh shall
            weigh 4.8 oz./sq.yd. (162 g/m2) and shall be shiftproof with trimmed roll edges to minimize buildup on
            overlapped seams.

2.07   Primer


A.         STO PRIMER - a ready-mixed elastomeric acrylic dispersion based primer with fine aggregate that             can be tinted to match the finish coating; for use prior to the application of Sto acrylic textured finishes.

Note:     Priming is recommended to reduce substrate  absorption and to enhance finish color, to improve adhesion
            and water resistance, and to retard efflorescence in cementitious substrates.  Appropriate tinted primer is
            recommended as a color base for “R” (rilled textured) finishes and all fine aggregate (less than 1mm)

2.08  Textured Coating  (select one, depending on type, texture desired)

A.         Sto elastomeric textured coatings:

            1. STOSILCO FLEX - a ready-mixed silicone based elastomeric textured wall coating with graded marble
            aggregate (as listed below) for trowel or spray application.

                                    Texture                                      Aggregate Gradation
                        Stosilco Flex 1.0                                                 .8-1.2mm
                        Stosilco Flex 1.5                                                 1.2-1.8mm
                        Stosilco Flex R1.5                                                    1.2-1.8mm

B.         Type, texture, color and aggregate size of coating shall be as indicated on architectural drawings or per
            approved sample submittal.  Lightness value shall be 30% or greater for Sto silicone based finishes, 20%
            or greater for all others.

2.09   Performance Criteria

A.         All materials shall meet or exceed the minimum performance criteria listed in this specification:   

1. Stucco Patching/Leveling/Resurfacing Material* (Sto One Coat Stucco or Sto Leveler):

TEST                                              METHOD                        RESULT  
Compression Strength                  ASTM C - 109               Greater than 4000 psi

Tensile Strength                          ASTM C - 190               Greater than 300 psi

Flexural Strength                         ASTM C - 293               Greater than 1000 psi

Water Absorption                        ASTM C - 642               Less than 3%

Surface Burning                           ASTM E - 84                 Flame spread - 0    Smoke developed - 0

*all results @ 28 days


2. Waterproofer and Stucco Crack Repair Ground Coat  (Sto Flexyl):

TEST                                              METHOD                       RESULT

Tensile Strength                          ASTM D - 412               300 psi

Elongation                                 Lab method                    7.7% (w/o mesh)

Adhesion to cement board              ASTM C - 297               100 psi

Adhesion to concrete                    ASTM D -4541               90 psi

Adhesion (in peel) to concrete        ASTM D - 903               20 lb.

Vapor Permeability                      ASTM E - 96                 1.20 US perms

Mandrel Bend                              ASTM D - 522               pass @-30 degrees C, 0 degrees C, 30 degrees C
Hydrostatic Pressure                     Lab Method                    no water penetration at 7 bar (230 foot height
                                                                                                water column) after 24 hours.
Waterproofing                             ASTM E - 514                    no water penetration after 8 hours exposure

UV Resistance                            ASTM D - 822               no degradation

Surface Burning                           ASTM E - 84                 flame spread: 25             
                                                                                                smoke developed: 70

3.   Elastomeric joint  compound (Sto Flexjoint Compound)
TEST                                        METHOD                      RESULT

Tensile Strength                          ASTM D - 412               60 psi

Elongation %                              ASTM D - 412               500%

Recovery @ 100% elongation        ASTM D - 412               70%
                                                            (10 min. recovery)

Shore “A” Hardness                      ASTM D - 2240              25 - 30


4.   Silicone based elastomeric paint (StoSilco Lastic) :

TEST                                        METHOD                      RESULT

Accelerated Weathering                 ASTM G - 53                 no noticeable yellowing or deterioration
                                                                                    or delamination @ 2000 hours.
Freeze/Thaw                               Lab method                    no cracking, discoloration or loss of film
                                                                                    integrity after 25 cycles
Tensile Strength                          ASTM  D - 412              135 psi

Elongation                                 ASTM D - 412               280%

Recovery at 175 % Elongation       ASTM D - 412               80%

Water Vapor Transmission            ASTM D -1653               9 - 10 perms @ 20 mils
                                                (method A)
Adhesion                                    ASTM C - 297               145 psi (wood)
                                                (modified)                       greater than 45 psi (steel)
                                                                                    greater than 140 psi (concrete)

Water Absorption                        DIN 52 617                    .054 kg/squ m/24 hr @ 3 weeks

TEST                                        METHOD                      RESULT

Intercoat Adhesion                       ASTM  D - 3359             5
Shore “A” Hardness                      ASTM D - 2240              35 - 40

Mildew Resistance                       ASTM G - 21                 no mildew growth at 21 days

Crack Bridging                            Lab Method                    6.34 mils at 77 degrees F

Low Temperature Flexibility         ASTM D - 522               pass at -30 degrees C

5. Silicone Based Elastomeric Textured Coating  (StoSilco Flex SW1)

TEST                                        METHOD                      RESULT
Accelerated  Weathering                ASTM G - 53                 No deterious effects after 2000 hours.  No noticeable
                                                ASTM D - 659               yellowing. Chalk rating = 9 (10 is best on a scale of
                                                ASTM E - 313                1 - 10 )

Elongation                                 ASTM D - 412               500% *

Tensile Strength                          ASTM D - 412               60 psi

Adhesion to Concrete                   ASTM C - 297               120 psi

Flexibility                                  ASTM D - 522               pass at 1/8 inch mandrel bend at - 30 degrees F

Freeze/Thaw Resistance                Lab Method                    no change after 25 cycles

Water Vapor Permeance                ASTM D - 1653              34 perms

Mildew Growth                           ASTM G - 21                 no growth

Chemical Resistance                    ASTM D - 1306              good resistance to Mild Acids, Alkalis and Salts

Resistance to Dirt Pick-up             Lab Method                    98% reflectance retained

Wind Driven Rain                        Fed Spec TT-C-555B        pass

Surface Burning                           ASTM E - 84                 Flame Spread: 5
                                                                                    Smoke Developed: 5
*elongation of neat film

*all results after 7 days

2.10   Mixing

A.         Sto Plex W - mix with a clean, rust-free high speed mixer.  Add water as directed on labeling.

B.         Sto Bonding Agent - As a bonding agent, agitate container and use undiluted.

C.         Sto Leveler - mix with 6 -7 quarts of clean potable water per 60 lb. bag, allow to set for approximately
            5 minutes, adjust mix  if necessary, then remix to a uniform consistency.

D.         Sto One-Coat Stucco - mix approximately 200 lb. of sand to an 80 lb. bag of Sto One -Coat Stucco.  Add preblended dry mix to 5 -7  gallons of clean potable water.  mix with paddle type mortar mixer to a uniform consistency.

E.         Sto Acrylic One-Coat Stucco - dilute Sto Bonding Agent  with 3 parts water to one part Sto Bonding  Agent (by volume).  Follow normal mix ratio and procedures for mixing Sto One-Coat Stucco, except use 5-7 gallons of diluted Sto Bonding Agent in lieu of water.

F.         Sto Textured Finishes - mix with a clean, rust-free high speed mixer.  A small amount of clean water may
            be added to aid workability



A.         All installation of Sto materials shall be performed by and/or supervised by Sto Instructed* Applicators.

B.         Under no circumstances shall any of the products be altered by adding any additives, except for small
            amounts of clean water as directed on the label. Antifreeze, accelerators, rapid binders, aggregates, etc., are forbidden.

C.         The surface to receive the stucco repair system shall be structurally sound, clean, dry and free of residual
            moisture or damage from moisture.  Surfaces shall be properly cured and free of dirt, dust, oil, grease,
            mildew, fungus, laitance, efflorescence and any other contaminant.  Any surfaces not in compliance shall
            be corrected prior to installation of the stucco repair system:

                        1.  Surface contaminants must be removed by wire brush, sandblasting, waterblasting or other
                             appropriate means.
                        2.  Efflorescence may be removed by a diluted acid wash and rinse, or other appropriate means.
                        3.  Treat dry, porous, or absorbent surfaces with surface conditioner.  (Use Sto Plex W for highly absorbent, sanding surfaces and chalking surfaces.)
                        4.  For painted surfaces: paint must be removed by wire brush, sandblasting, waterblasting  or
                             other appropriate means.  Alternate procedure for LOAD BEARING painted surfaces ONLY:
                             treat with water based surface conditioner.
                        5.  If patching, filing or leveling of irregularities is requited, and to repair loose, deteriorating
                             plaster, concrete, or mortar, repair with appropriate leveling material to thickness required to achieve a smooth, plumb surface.


D.         Crack Repair and resurfacing of cementitious stucco:

  1. For cracks up to 1/16 inch, reinforce with minimum 6 inch wide mesh embedded in elastomeric ground coat. For larger cracks, clean out loose material with trowel, prime inside  surfaces of crack with diluted bonding agent and fill with stucco patching/leveling material.  Allow to dry and reinforce with minimum 6 inch wide Sto detail mesh embedded in ground coat.


Note:  If cracks are widespread throughout the wall area reinforce entire area with Sto mesh embedded in
          Sto Leveler or elastomeric ground coat.

  1. After properly preparing surfaces, patch/level all voids or surface irregularities with a trowel application of the patching/leveling surface.  Where adverse drying conditions exist (dry climate and/or temperature above 80 degrees F, damp cure the area to prevent shrinkage and enhance material strength.


 .     When resurfacing entire wall area, prepare surfaces in accordance with Section 3.01C.  Apply stucco
       resurfacing material by trowel or with proper spray equipment to a maximum 3/8 inch thickness in one
       application. Apply second coat if necessary to achieve a smooth, plumb surface as soon as the first coat is
       firm enough to receive the second coat without physical damage.  Alternatively, damp cure the first coat
       for 48 hours, then apply the second coat.  Level with a darby or stainless steel trowel.  Damp cure by lightly
       fogging the installed area for at least 48 hours after initial set (usually within the first 1 to 4 hours after
       prior to application of primer or finish.

F.         Waterproofing:  any areas requiring a waterproof membrane, such as sloped sills or parapets, shall be
            treated following crack repair/leveling or resurfacing and prior to application of the textured finish:

  1. Apply ground coat with stainless steel trowel to a uniform thickness of approximately 1/16 inch. Work horizontally or vertically in uniform strips of 40 inches.

                        2.   Immediately embed reinforcing mesh in wet ground coat and feather out seams and edges.

  1. Double wrap reinforcing mesh at all corners and overlap at the seams not less than 2-1/2 inches.
  2. Apply mesh a minimum of 6 inches beyond sloped sill terminations or down both sides of the parapet (where stucco is on both sides).
  3. The finished thickness of the ground coat shall be such that the mesh is fully embedded.  Allow to dry prior to application of textured finish or primer.

Note:     Retaining walls must be properly waterproofed before application of Sto products to the exterior face of the retaining wall. Absolutely no exceptions.
Note:     Parapets and sills must be sloped to shed water. Terminations at windows or at roofing material must be properly flashed and/or caulked to prevent water infiltration behind the waterproofing application.

G.         After preparation and repair of all surfaces the textured finish application may begin.  Where a primer
            is used apply with brush, roller or proper spray equipment to the substrate and allow to dry thoroughly
            before applying the textured finish coating.  The textured finish shall be applied by spraying or
            troweling with a stainless steel trowel.  General rules for application of finish are as follows:

            a.  Avoid application in direct sunlight.
            b.  Apply finish in a continuous application, always working to a wet edge.
            c.  Weather conditions affect application and drying time.  Hot or dry conditions limit working time and
                 accelerate drying and may require adjustments in the scheduling of work to achieve desired results;
                 cool or damp conditions extend working time and retard drying and may require added measures of
                 protection against wind, dust, dirt, rain and freezing.
            d. “R” (rilled texture) finishes must be floated with a plastic trowel to achieve their rilled texture.
            e.   Avoid installing separate batches of finish side-by-side.
            f.   Avoid application over irregular surfaces, especially with smaller aggregate finishes, which will not
                 hide deviations in the plane of the surface.

*The holder of the Sto Certificate has been instructed by approved Sto Instructors in the correct application and

handling of specific Sto Materials.  However, the applicator is an independent contractor and Sto Corp. cannot control the manner of his/her work nor can it guarantee that the applicator will correctly apply and handle all Sto Materials.



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