Designation: C 946 91 (Reapproved 2001)Standard Practice forConstruction of Dry-Stacked, Surface-Bonded Walls1ThisstandardisissuedunderthexeddesignationC 946;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1Thispracticecoversmaterial, workmanship, andcon-structionprocedures for applyingsurfacebondedmortar toboth sides of dry stacked concrete masonry units. It does notincludegrout, reinforcing, anchorage, orcontrol jointssincetheir use is essentially the same as conventional concretemasonryconstruction, unless specicallymentionedinthispractice.NOTE 1Design and construction procedures for conventional concretemasonry construction have been written by the American ConcreteInstitute, Building Code Requirements for Concrete Masonry StructuresandtheNationalConcreteMasonry Associations,SpecicationfortheDesign and Construction of Load-Bearing Concrete Masonry.1.2The values stated in inch-pound units are to be regardedas the standard. The values given in parentheses are providedfor information only.1.3Thisstandarddoesnot purport toaddressall of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1ASTM Standards:C 55Specication for Concrete Brick2C 90Specication for Loadbearing Concrete MasonryUnits2C 129Specication for Nonloadbearing Concrete MasonryUnits2C 145SpecicationforSolidLoad-BearingConcreteMa-sonry Units3C 270Specication for Mortar for Unit Masonry2C 887Specication for Packaged, Dry, Combined Materialsfor Surface Bonding Mortar22.2 American Concrete Institute Standard:531Building Code Requirements for Concrete MasonryStructures, Commentary-ACI 531R-7942.3 International MasonryIndustryAll-Weather CouncilStandards:Recommended Practices and Guide Specications for ColdWeather Masonry Construction52.4 National Concrete Masonry Association Standard:Specication for the Design and Construction of Load-Bearing Concrete Masonry63. Storage3.1Deliver andstoresurfacebondingmortar inoriginalcontainers off the ground to prevent contact with water. Protectfrom rain with suitable covering.3.2Store concrete masonry units off the ground to preventcontaminationbymud, dust, andmaterials likelytocausestaining or other defects, and protect from rain.4. Materials and Manufacture4.1Concrete masonry units shall be clean and dry, meetingtherequirementsofTypeI, moisture-controlledunits, oftheapplicable ASTMspecication (Specications C 55, C 90,C 129, andC 145). Thesurfacetoreceivesurfacebondingmortar shall be free of paint, oil, efflorescence, or foreignmaterials that interfere with bonding.4.2Mortar shall be mixed in accordance with the proportionspecicationofSpecicationC 270andshallbeselectedonthe basis of Appendix X1 of Specication C 270.4.3Surface bonding mortar shall meet the requirements ofSpecication C 887. If the dry mix contains hard lumps, it shallnot be used.4.4Shims shall be corrosion-resistant metal or plastic witha minimum compressive strength of 2000 psi (13.8 MPa), orsteel protected from corrosion by a coating of zinc at least 0.8oz/ft2(2.4gm/mm2), orbyacoatingofcadmiumorzincofequivalent corrosion resistance.5. Leveling Courses5.1Leveling courses, when needed, are to provide a smooth1This practice is under the jurisdiction of ASTM Committee C12 on Mortars andGrouts for Unit Masonry and is the direct responsibility of Subcommittee C12.06 onSurface Bonding.Current edition approved September 15, 1991. Published November 1991.Originally published as C 946 81. Last previous edition C 946 84 (1989).2Annual Book of ASTM Standards, Vol 04.05.3Discontinued. See 1989 Annual Book of ASTM Standards, Vol 04.05.4Availablefromthe AmericanConcreteInstitute,P.O.Box9094,FarmingtonHills, MI 18333.5Available fromthe International Masonry Industry All-Weather Council,MasonContractorsAssociationofAmerica, 17W601FourteenthSt., OakbrookTerrace, IL 60181.6Available from the National Concrete Masonry Assn., P.O. Box 781, Herndon,VA 22070.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.surface level within14 in. (6.35 mm) in 20 ft (6.1 m), for drystackingconcretemasonryunits. Levelingcourses shall belocated whenever a vertical difference greater than12 in. (12.7mm) in10ft (3.0m) occurs withinone course. Levelingcourses are usually located on the rst course above thefoundation, because footings are not normally placed in a levelcondition, and at each oor level.5.2When mortar or surface bonding mortar is used alevelingcourse,concretemasonryunitsshallbesetinafullbedof mortar, laidtoalinewiththetopsurfacelevel, asdened in 5.1, and butted together with no mortar in the headjoints. Bed joints shall be struck ush. If the cores are to begrouted, no mortar shall be placed in the space to receive grout.5.3Allow mortar to set sufficiently so no movement breaksthe bond while dry stacking units in subsequent courses.6. Dry-Stacking Concrete Masonry Units6.1Courses of concrete masonry units between the levelingcoursesshall beplacedwithout mortar onthebedor headjoints. Placeunitsinrunningbond. Removeburrsandbuttblocks tightly.6.2Use shims, mortar, or surface bonding mortar to plumband level individual units when necessary.6.3Checkthewall everyfourthcoursetobecertainit isplumb and level. If any course is out of level by more than12in. (12.7 mm) in 10 ft (3.0 m) another leveling course shall bebuilt.6.4Cut masonry units to t openings. Minimum length ofcut piece used in the wall shall be 114 in. (31.8 mm).6.5Precut units for inserts indicated on drawings.6.6Anchors, reinforcing, ashing, lintels, and other items tobe built in shall be installed as the stacking progresses. Cut ornotch masonry units as required.NOTE 2Special consideration must be given to the placement of builtinitems. Surfacebondingmortar requiresapproximately114in. (31.8mm) from the edge of a unit to develop tensile strength across the joint.Layout of therst coursewithrespect tobuilt initems is extremelyimportant, it determines the size of the cut pieces for closure.NOTE 3Utilities such as electrical lines and plumbing located in thecores of theunits arebest placedprior totheapplicationof surfacebonding mortar while the concrete masonry units are visible.6.7Cores to be lled with grout shall be aligned to providea continuous, unobstructed opening.6.8Where a horizontal change in wall thickness occurs, thethicker portion shall end with a solid surface. Use a levelingcourse for the rst course in the upper portion.NOTE 4Dry-stacked, uncoated walls should be adequately braced.7. Mixing Surface Bonding Mortar7.1Use clean mixing equipment and water free of deleteri-ous amounts of acid, alkali, and organic materials.7.2Surface bonding mortar shall be mixed according to themanufacturersinstructionsandusedwithinthetimerecom-mended by the manufacturer.7.3Mix only full bag multiples of material to overcome anysegregation of ingredients while in the package.7.4Mixing time shall be kept to a minimum, as over mixingmay cause damage to the bers.7.5Hand Mixing:7.5.1Place water in the mixing container.7.5.2Slowly add the dry surface bonding material.7.5.3Mix thoroughly.7.6Machine Mixing:7.6.1Place water in mixer.7.6.2Addthe surface bondingmaterial tothe operatingmixer.7.6.3Mixthoroughly, 1to3minafterall materialshavebeen added.7.7The mixture should be creamy, nonlumpy, and easy toapply.7.8AdmixturesmaybepermittedwithinthelimitssetbySpecication C 887 and the manufacturer of the surfacebonding mortar. If desired, admixtures must be specied in thecontract documents.8. Application of Surface Bonding Mortar8.1Wet the wall uniformly with water immediately beforeapplying surface bonding mortar to prevent excessive suctionof water from the surface bonding mortar. If the wall dries priorto application, rewet it. Avoid saturating the units.8.2Trowel- or spray-apply surface bonding mortar to bothsides of the dry-stacked concrete masonry units.8.3Completelycover the wall surface witha minimumthicknessof18 in. (3.2mm) of surfacebondingmortar bytrowel or spray.8.4When a second coat of surface bonding mortar is to beapplied, the rst coat shall have taken its initial set but not becompletelyhardenedordriedout. Iftherst coat hascom-pletely hardened or dried out, consult the manufacturersrecommendations for applicationof asecondcoat, sinceabonding agent may be required.8.5Finish to the texture specied.8.6If application of surface bonding mortar is discontinuedfor more than 1 h, the horizontal joint between the twoapplications, other than at wall tops, must occur at least 114 in.(31.8 mm) from the horizontal edge of the concrete masonryunit.9. Curing and Protection9.1Surface bonding mortar shall not be applied at tempera-tures below40F(4.4C) unless theInternational MasonryIndustry All Weather Councils Recommended Practices andGuide Specications for Cold Weather Masonry Constructionare followed.9.2Dampen the wall with a water mist after 8 h, but within24 h of application of the surface bonding mortar.9.3Fog spray twice within the rst 24 h from application ofthesurfacebondingmortar. Withpigmentedmortarthetimemay be extended to 48 h. With maximum temperature in excessof 90F (32.2C), wind speed greater than 20 mph (32.2 km/h),or meanrelativehumiditylessthan50 %relativehumidity,more frequent application of fog spray shall be necessary.9.4The top of the walls shall be covered with a nonstaining,waterproofcovering, extendingatleast2ft(0.6m)oneachside of the wall to prevent moisture from entering the wall untilthe top is permanently protected.C 946210. Other Requirements10.1Requirements concerning grout, reinforcement, an-chors,ties,corrosionresistance,dimensionaltolerances,wallbracing after coating, and miscellaneous items unless speciedbythemanufacturer of thesurfacebondingmortar shall beoutlined in the following:10.1.1Building Code Requirements for Concrete Structuresand Commentary by the American Concrete Institute.10.1.2Specication for the Design and Construction ofLoad-Bearing Concrete Masonry.10.2Control Joints:10.2.1Location, spacing, andtypeof control jointsshallmeet the requirements of the standards referenced in 10.1.10.2.2Control joints shall be uniform in width, through thewall, and continuous from top to bottom of the wall.10.2.3Remove surface bondingmortar fromthe controljoint.11. Keywords11.1dry stacked; ber reinforced; mortar; packaged; surfacebondingASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every ve years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,UnitedStates. 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