L

i

CONTENTS

Page

Advantages of surface bonding ................. 1Preliminary planning ......................... 2Preparation for surface bonding ................ 3Foundation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Tie-down rods .............................. 5Floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Erecting the walls ........................... 5

Tying intersecting walls .................... 7Control joints. ........................... 7Lintels and sills .......................... 8Windows and doors ....................... 8Installing electrical switches

and outlets ............................. 10Installing tie-down rods .................... 11Insulating the wall ........................ 11Installing the plate ........................ 12

PageBasement construction ....................... 12Other construction details. .................... 13

Pilasters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Beams or joists ........................... 13

Surface bonding the walls ..................... 14Commercial surface bonding

premixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Ingredients for home-mixed

surface bonding ......................... 15Home mixing the materials ................. 15Applying the bonding mix .................. 16Coverage of the bonding mix ................ 17Time requirements ........................ 17Sanded bonding mix ...................... 17

Painting surface-bonded walls .................. 18CAUTION STATEMENT .................... 18

PREFACE

Agricultural Research Service research on surface bonding began in 1967 and is being continuedon a limited basis in cooperation with the Agricultural Engineering Department of the University OfGeorgia’s College of Agriculture at College Station, Athens, Ga. The work contributes to SouthernRegional Housing Research Project S-66, “Physical, Social, and Economic Aspects of FunctionalHousing for Low-Income Families,” sponsored by the State Experiment Stations of Georgia, NorthCarolina, South Carolina, Texas, and Virginia, and the Agricultural Research Service, the CooperativeState Research Service, and the Forest Service of the U. S. Department of Agriculture.

Tests by the National Concrete Masonry Association show that surface bonded walls are strongenough for two-story construction. Commercial buildings with walls 14 feet high have beensuccessfully constructed.

The E-type glass fiber used as reinforcing in the surface-bonding mix has, after application to testwalls, shown no etching or loss of flexibility when exposed to the weather over a 39-month period.The regular type I gray cement used in the mix is much higher in alkalinity than white cement sothat the reaction of the gray cement on the fibers would tend to be more severe. The fact that thefibers have withstood this reaction is evidence of probable continued durability under normalbuilding conditions. The use of white cement would be an added safety factor.

An alkali-resistant fiber has been developed by one U.S. concern, and a bonding mix containingthis fiber is on the market. The use of this fiber would be desirable under high-alkali conditions andcontinuous high-moisture exposure, such as in swimming pools and deep tanks.

The first Agricultural Research Service publication on surface bonding was issued January 1970as Correspondence Aid 42-57, “Surface Bonding-A Technique for Erecting Concrete Block WallsWithout Mortar Joints.” This was superseded by U.S. Department of Agriculture InformationBulletin No. 343, “Surface Bonding of Concrete Blocks,” in June 1970. The present edition of thebulletin is a complete revision incorporating more detailed instructions and the experience gainedsince the first publication.

Supersedes Agriculture Information Bulletin No. 343“Surface Bonding of Concrete Blocks”

SLtechnwith<a tenbothtogetbloc1

Ntar. (not c’It sebloc1strension.corn]negli

Fpletkof rCapilcraclBeinalsoblocby tl

ICOUIThisingc

1,HourAthe

IvAgritingRaeRemB O X

ii

pbge. 12* 13* 1313

14

14

15151617 \17 I

17 ~18 i18

1

uedY ofiernsndxth.tive

ong

iod.L sothemal

ingmd

170tills

i

ion 1he I

ed

CONSTRUCTION WITH SURFACE BONDING

byB. Carl Haynes, Jr., P.E., and J.W. Simons, P.E.’

ADVANTAGES OF

Surface bonding is both a material and atechnique for erecting concrete-block wallswithout mortar joints. The bonding material isa cement-glass fiber mixture that is troweled onboth sides of the stacked blocks to hold themtogether. No mortar is used between theblocks.

Normally, concrete blocks are laid in mor-tar. Contrary to popular belief, the mortar doesnot act as a “glue” to hold the blocks together.It serves mainly as a bed to aid in leveling theblocks. Mortar joints have little, if any,strength in tension and relatively poor adhe-sion. For structural purposes other than directcompression, the strength of a mortar joint isnegligible.

Furthermore, mortar joints do not com-pletely tighten the wall against the penetrationof rain. The mortar joints actually serve ascapillary wicks and draw moisture through thecracks between the mortar and the blocks.Being extremely porous, the blocks themselvesalso soak up water. Accordingly, a concreteblock wall laid in mortar must be waterproofedby the application of a sealing compound.

In surface-bonded block walls, only the firstcourse is bedded in mortar or bonding mix.This permits the accurate and rapid dry-stack-ing of subsequent courses.

‘Both formerly Agricultural Engineers at theHousing and Environmental Engineering Laboratory inAthens, Ga.

Mr. Simons is retired. Mr. Haynes is currentlyAgricultural Engineer at the Environmental Engineer-ing Laboratory, Richard B. Russell AgriculturalResearch Center, Southern Region, AgriculturalResearch Service, U.S. Department of Agriculture, P.O.Box 5671, Athens, Ga. 30604.

SURFACE BONDING

Surface-bonded-or “skin-stressed”-concreteblock walls are stronger and tighter thanconventionally laid walls. When the surfacebonding mixture on the wall has cured, itwill have relatively high tensile strength andgood adhesion to the wall. Any flexure of awall section is resisted to the limit of thebonding-tensile strength, and that strength isgenerally about six times that of convention-ally mortared block walls.* Also, the surfacebonding mixture becomes a waterproof coatingfor the walls. (Swimming pools and deep tankswill need additional waterproofing such asspecial latex paint or epoxy paint.)

Another advantage of surface bonding is itseconomy: fewer hours are needed for wallconstruction, and less-skilled labor can bereadily trained to apply surface bonding.3

Surface bonding offers a variety of “natu-ral” color and finish possibilities. The walls canbe permanently colored without painting byadding mortar color or concrete color to thebonding mix. The bonding material itself candry to either a smooth or stucco-type finishdepending on how it is applied.

*Extensive test data for surface bonding is con-tained in “Research Bulletin 110: Surface Bonding ofConcrete Block Walls as Related to Structural Proper-ties,” published by the Agricultural Research Service,USDA, in cooperation with the University of Georgia.Copies of this bulletin can be obtained by writingEditor’s Office, College of Agriculture ExperimentStations, University of Georgia, Athens, Ga. 30602.

3 National Concrete Masonry Association compara-tive tests, reported in NCMA-TEK 54, show that amason’s productivity is increased 70 percent byutilizing surface bonding in lieu of mortared construc-tion.

1

PRELIMINARY PLANNING

Select a site that requires minimum excava-tion, has sufficient stability for the type offoundation proposed, has good drainage, and isnot subject to flooding.

Plan for water supply and sewage disposal.This may require consultation with publichealth authorities.

Determine if a building permit is required inthe area where you intend to build. Buildingcodes may be administered by the city, county,or state. County offices can usually furnishpermit information.

Decide who will be doing the actual con-struction work. Will you do all the construc-tion, sub-contract part of the construction, orcontract for the finished (complete) building?

Sub-contracting such items as a concrete slabfloor, plumbing, and heating may be necessaryto allow completion within desired time limits.

An accurate layout of the structure isessential before you begin to build (fig. 1).Keep in mind that without mortar joints theoverall wall dimensions will not be modular,that is, on &inch or 16-inch centers . Thelengths and heights of walls and wall openingsconstructed with standard-size blocks withoutmortar joints are given in the table. Since manyblocks are not uniform in size and may oftenbe tapered, add one-fourth inch to the lengthsgiven in the table for each approximate 10 feetof wall.

Dimensions of Walls and Wall OpeningsConstructed with Surface-Bonded Concrete Blocks’

NumberO f

blocks

Length of wallor

width of doorand window openings2

Numberof

courses

Height of wall

height’zf doorand window openings 3

::34

:

:9

101112131415

1’ 3 5/B”2’ 7 l/4”3’ 10 7/8”5’ 2 l/2”6’ 6 l/8”7’ 9 3/4”9’ 1 3/B”

10’ 511’ 8 518”13’ 0 l/4”14’ 3 7/8”15’ 7 l/2”16’ 11 l/8”18’ 2 3/4”19’ 6 3/8”

1

:45

;89

101112131415

7 518”1’ 3 l/4”1’ 10 7/8”2’ 6 l/2”3’ 2 l/8”3’ 9 3/4”4’ 5 3/8”5’ 15’ 8 5/8”6’ 4 l/4”6’ 11 7/B”7’ 7 l/2”8’ 3 l/B”8’ 10 3/4”9’ 6 3/8”

Standard 18inch blocks, E-5/8 inches long by 7-5/8 inches high.‘Add onefourth-inch for each approximate 10 feet of wall to allow for nonuniformity in sizeof blocks.“Make a trial stacking of blocks to determine the actual height of wall or opening beforebeginning

construction.

Figurlir(Ebcbc

Tbloc:ture

0

tom

(thl:tae

0tran,

amet;tam:for 1ing.:

athe14-i

4tovbonbon

4the

2

Figure l.-Layout of the building must be accurate. Square building lines, marking with stakes at corners. Marklimits of excavation with stakes. Position, erect, and level batter boards 4 to 10 feet from excavation lines.(Excavation lines should be at a sufficient distance from building lines to allow workman to apply surfacebonding.) Attach lines to batter boards above building lines. After excavation is complete, building corners canbe located simply by dropping plumb line from lines on batter boards.

PREPARATION FOR SURFACE BONDING

The following items are needed for stackingblocks and applying the surface bonding mix-ture:

l Wheelbarrow, small mortar box, or tub-to mix and hold the bonding mix.

l Garden cultivator, rake or weeding hoe(three- or four-tine)-to mix the dry ingredientstogether and with the water.

l Bricklayer’s trowel-to aid mixing and totransfer the mix to hawk.

l Hawk (a small board or piece of squaremetal with a handle attached to the bot-tom)-to carry the bonding mix. (See fig. 2for hawk designed especially for surface bond-ing.)

l Plasterer’s trowel-to spread and smooththe bonding mix (3 l/2- by 12-inch or 4- by14-inch is the most suitable).l Garden hose with fine-spraying nozzle-

to wet down the block wall before applying thebonding mix, and to spray water onto thebonded wall to aid in curing the mix.

l Carpenter’s or mason’s level-to checkthe walls to be sure they are horizontal and

vertical. Use the level at least every thirdcourse.

l Mason’s line (tightly braided nylon orcotton cord with wooden hooks)-to aline theblocks in stacking the wall.

l Rubber-coated gloves-to protect thehands.

In addition, if holes are to be drilled andexpansion bolts set into the cured concretefloor or footing for attachment of tie rods,some type of power-driven drill and a drivingtool will be needed. Hammer drills are best fordrilling concrete, but are often too expensivefor small jobs or a single house. An ordinaryelectric drill with carbide-tipped masonry bit isslower but satisfactory. The drilling can bedone with a star drill and hammer, but thisrequires more time. A drill, either hand orelectric, and bits are needed for drilling holes inthe plate to receive the rods and cables; ifelectric, the drill should be l/2-inch size.General carpenter tools will be needed in otherphases of the construction. A portable electriccircular saw saves time and is a good invest-ment.

3

Figure Z.-Homemade hawk designed especially forsurface-bonding work.

WOOD HANDLE

FOUNDATION

A concrete block building, like any build-ing, needs a solid foundation laid on undis-turbed or well-compacted soil. A level founda-tion or floor is the most important requirementbefore starting the first course of block. Highand low points should be within one-fourthinch of level in any lo-foot length of thefoundation or floor. Follow the general designrequirements for depth of foundation and useof reinforcing in your area.

In some areas-and for all basements- aseparate footing and foundation wall will beneeded (fig. 3). Foundation wall thicknesses

and depths allowable below grade (belowground level) for nonreinforced, hollow con-crete block walls, based on FHA minimumstandards for average soil conditions, are asfollows:

Foundation Maximum depth

wall thickness below grade

8” 5’

12” 7’

30.LB

Figure 3.-Footings should be twice as wide as the wall thickness. Install drain tile adjacent to the footing toprevent buildup of water pressure against foundation. Cover open drain tile joints with 30-pound asphaltedroofing felt. Backfill over tile with 12 inches of coarse gravel.

Inrods inot 1

serve

to the

age :convcPlatethree

c

.

Tior foiand fdrill Ihamnhashwithsionthee

Tjthanwind4 fethrowof aeach

Ucorn’the j

imta

I

c

P

ills

conemosexpcmucNotPra‘ShOl

L

6%St01

of 1line

4

TIE-DOWN RODS

In surface bonding construction, tie-downrods are fastened to the foundation. They arenot needed for wall strength. Rather, theyserve to tie the wood plate on top of the wallto the foundation. This provides better anchor-age for the roof structure than does theconventional method of setting relatively shortplate bolts into the concrete-filled top two orthree courses of blocks.

Tiedown rods can be attached to the flooror foundation with expansion bolts. The easiestand fastest method to install these bolts is todrill holes into the floor or foundation with ahammer-type concrete drill after the concretehas hardened (fig. 4). An ordinary electric drillwith a masonry bit may also be used. Expan-sion bolts are then expanded in the holes afterthe concrete has cured for at least 7 days.

Tie-down rods should be installed not morethan 6 feet apart along exterior walls. In highwind areas, space tie-down rods not more than4 feet apart. Rods should also run downthrough the block cores adjacent to each sideof a door opening, and at building corners oneach side.

Figure 4.-Drilling to install expansion bolts. Prelimi-nary placement of the first course of blockswithout bedding them in mortar enables the builderto accurately position bolts in the centers of blockcores, A bubble mounted on the drill to aid indrilling the holes vertically may be used in place ofthe drilling guide shown. The guide cannot be usedif the first course of blocks has already beenbedded in mortar.

FLOOR

If a concrete floor is used, it is important tocomplete all rough plumbing before pouring. Ifthe floor is poured separately from the footing,install expansion joints as shown in figure 3.

.

A concrete slab floor on grade may be usedin some areas (fig. 5). Specify 3,000-poundconcrete in place of the 2,500-pound concretemost often used. Although it is slightly moreexpensive, the 3,000-pound concrete worksmuch more easily and is less liable to crack.Note reinforcing in figures 3 and 4; commonpractice that provides good results in your areashould be followed.

WELDED WIRE MESH

REINFORCING STEE

Figure 5.-Concrete slab floor on grade. Install bolts

for tie-down rods.

.

ERECTING THE WALLS

Unless prohibited by the building code, &inch-thick walls must be used for two-storyg-inch-thick block walls may be used in one- houses.4 The basement is included as onestory, single-family dwellings when the heightof the wall does not exceed 9 feet at the plate 4HUD Minimum Property Standards for One- andline and 15 feet at the peak of any gable; Two-Family Dwellings.

5

story. (See tabulation on page 4 and sectionentitled “Basement Construction” for requiredthickness of basement walls.) Lightweightblocks bond best and are strong enough fortwo-story construction.

Stretch mason’s lines to the dimensions ofthe building and at the proper height to alinethe first course of blocks. Lay the first courseof blocks in rich mortar mixed by volume asfollows: masonry cement-l part; portlandcement-l/2 part; and sand- 2 l/2 parts (fig.6). Use a stiff mixture if a thick mortar bed isneeded to level the first course. To avoidsettling, allow the mortar to set up beforestacking additional courses.

Lay succeeding courses of blocks withoutmortar. The tops of most blocks are somewhatrough. Slide the blocks back and forth a coupleof times over other blocks to knock off excessmaterial and burrs before stacking them,

Stack the blocks three courses high atcorners and plumb (fig. 7). Stretch mason’s linebetween corners. Then fill in between comersand door and window openings with blocks(fig. 8). Repeat the procedure with anotherthree courses of blocks.

High-quality blocks do not vary much inany dimension. Check the blocks before youbuy them, and find a supplier who can furnish

.Figure 7.-Stack blocks at corners three courses high

and plumb with mason’s or carpenter’s level.

Figure B.-Lay the first course of blocks in richmortar on the slab floor or footing.

Figure 8.-Mason’s line held between corners withwooden hooks. Lay wall without mortar to line.

toprPi!

St1

h”fSittic

Wi

titas

.

.

uniform blocks. Blocks that are not dimension-ally true may be plumbed and leveled byinserting flat sheet-metal shims or brick tiesbetween them (fig. 9). Do not use wood shimsor spacers. If the height of the blocks varies bymore than one-eighth inch, bed the shortblocks in mortar or bonding mix to correct theexcessive height difference.

Use sash blocks with slotted ends to formthe sides of window and door openings. Theside fins on metal windows or the stops onwooden windows and door frames fit into theslots to hold windows and doors in place.

Tying Intersecting Walls

Walls that intersect should be tied togetherto strengthen the walls against lateral pressures.Properly constructed intersections can serve aspilasters. (See section on pilasters, page 13 ).

The corners of exterior walls can be con-structed integrally-i.e., with the conventionalsaw-toothed or interlocking arrangement ofheader blocks extending alternately from eachside of the intersection. This type of construc-tion should involve exterior walls only.

Intersections of partition walls with exteriorwalls should be reinforced with metal straps, ortie-bars. The procedure is essentially the sameas with conventional block wall construction.

Figure 9.-Insert metal shims between blocks if neces-sary to level or plumb the wall.

The ends of the tie-bars-turned down about 4inches-are set into block cores filled withmortar or concrete. However, since there areno mortar joints in surface bonding, the websof the blocks must be notched in order to“bed” the tie-bars. (fig. 10).

Control Joints

Control joints, always running the fullheight of the wall, may be required to preventcracking in long concrete block walls. They arenormally used in climates where temperaturesvary widely, causing considerable expansionand contraction of the walls. The local exper-ience of architects, engineers, and reputablebuilders as to the need for control joints is apractical guide. Generally, these joints arespaced 20 to 30 feet apart.

Special attention should be given to controljoints in the design of residences to avoid anundesirable appearance. For example, controljoints can sometimes be hidden behind down-spouts.

A wooden panel, such as might be used ininstalling a door, will serve as a control joint(fig. 11). The blocks should not be stacked too

Figure lo.-Tie bars set in block cores filled with con-crete or mortar to tie intersecting walls together.

Figure Il.-Wooden door panel, if it runs the fullheight of the wall as shown, may serve as a controljoint. Photograph shows paper covering on thepanel to prevent staining when surface bonding isapplied to wall.

tightly against the wooden panel. Fill theexterior joints between the panel and blockswith a flexible caulking to seal against rain andwind. In residences or farm and commercialbuildings, control joints may also be made inthe wall (fig. 12) or at pilasters. Preformedgaskets and special blocks are also available tomake control joints.

Wood frames for suspended floors shouldnot press tightly against concrete block walls.Otherwise, swelling of the wood in highhumidity combined with contraction of theblock walls in winter may cause walls to crack.

Lintels and Sills

Install lintels and sills in surface-bondedwalls as you would in building with conven-tional mortar joints. Precast reinforced-concrete lintels (fig. 13) or steel angles arenormally used. Special bond beam or lintelblocks are available in some localities. Rein-

forcing bars are inserted in these blocks, whichare then filled with concrete to make stronglintels (fig. 14). The lintels need not be set inmortar. Apply surface bonding over the facesof the lintels to provide a finish matching theWall.

Windows and Doors

Windows and doors may be prefabricatedinto wood frame panels designed to fill theexact space that would be occupied by severalwhole blocks (fig. 15). For example, a three-block space normally measures 3 feet 10 ‘7/8inches. Allow a full 3-foot ll-inch opening sothe panels will not fit too tightly.

Fasten wooden stops or steel channels tothe sides of the panels to fit into slots in thesash blocks forming the sides of the windowand door openings.

Staple expanded metal to the interior sideof the panel (except for the window or dooropening) so that it can be surface-bonded,giving a uniform interior wall finish around andbetween all windows and doors. The surfacebonding will not adhere to most buildingboards without the expanded metal covering.

An outside facing for the panels of 3/8-inch,stained, exterior plywood with a channel-groove, striated, or rough-sawn surface makes areasonably priced and durable finish. One-fourth-inch plywood is adequate for theinterior. Glue and nail the plywood to thewood frame. An adhesive applied to framingmembers with a caulking gun is the easiest andfastest method of gluing. On window panels letthe plywood extend downward over the con-crete sills on the outside to provide a drip edge.

To secure the panel in the wall, drive nailsthrough the top plate into the top of the panel,and fit the window panel over a concrete sill atthe floor. These procedures will result in firmlyfixed window panels.

Fasten door panels similarly. A weather-stripped threshold will brace the door frame atthe floor.

Electrical outlets can be more easily instal-led in a wood frame panel than in a concreteblock wall. The wiring can be connected beforethe interior finish is applied. Lead the wiringthrough the plate at the top, and leave asufficient length to tie into a connection box.

8

Figure 12.-One type of control joint. The joint must extend the full height of the wall.

PRECAST CONCRETE LIN

STEEL REINFORCiNG

TEL

Figure 13.-Precast reinforced-concrete lintel.

LINTEL BLOCKS WITHFILLED CONCRETE CORES

r STEEL REINFORCING

Fi

Figure 14.-Lintel made from bond beam or lintel blocks. Provide with reinforcing bars and fillwith concrete as shown.

Concrete blocks may be cut to provideopenings for standard-size windows. Severalsizes of standard windows can be installed inthe walls without cutting blocks. Other sizesmay be ordered specially. Direct installation ofwindows in block walls will eliminate thewooden panels. This can reduce constructiontime and cost.

Installing Electrical Switches and Outlets

Figure 15.-Prefabricated wood frame window panelwith exterior finish of rough-sawn plywood.

Electrical switches and outlets to be placedin the walls should be installed as the walls arebeing stacked. Saw openings in the block shellto fit the electrical boxes (fig. 16). Use aportable power saw equipped with a specialcarborundum blade for sawing concrete. Light-weight blocks are much easier to saw thanregular sand-cement blocks. Fasten the elec-trical box in the cut opening with machinescrews through the threaded holes in the box(fig. 17).

When electrical blocks are stacked in the

W

Ir1 0FlblC6

CE

aCC

ticthTsi

Fi

10

Installing Tie-Down Rods

Figure 16.-Saw openings in the concrete block tomount an electrical switch or outlet box.

wall, remove one or more knockouts as needed.Insert a puller wire through the knockout holelong enough to reach above the top of the wall.Feed the wire through the cores above as theblocks are stacked. Nonmetallic sheathed cablecan be fed through the cores and the box; thecable should be long enough to extend througha hole in the plate and reach a central box forconnection to other outlets and the distribu-tion panel. Type NM cable can be used wherethere is not excessive moisture or dampness.Type NMC or UF must be used in damp or wetsituations.

Figure 17.-Electrical outlet box mounted in sawedopening in concrete block. Box is fastened intoblock with 8/32 machine screws with slotted heads.

Figure the length of 3/8-inch-diameter tie-down rods measured to include the height ofthe stacked-block wall, plus one layer ofl/2-inch-thick asphalt-impregnated fiberboard(seals against rain and wind between the plateand the top of the concrete blocks), plus thethickness of the plate (one or two thicknessesof lumber). Add 2 inches to this calculatedlength to allow for bedding the first course inmortar and for variations in block height.

Thread three-fourths to l-inch of one endof the rod. Thread three inches of the otherend. Screw a rod connector, similar to a pumprod connector, onto the short-thread end ofthe rod. Lower the rod, connector-end down,into the block core. With a flashlight locate thetie-down bolt, and screw the connector onto it(fig. 18).

Insulating the Wall

Fill appropriate core spaces with insulationbefore installing the plate and before surfacebonding the wall. Pellet insulation such asperlite or expanded mica is the best insulationfor this purpose. The insulation is treated witha silicone to resist moisture absorption. Prod-ucts of this type on the market usually contain

Figure 18.-Attach connecter end of rod to thetie-down bolt set into the concrete footing or floorslab.

11

a large percentage of fine particles that tend toflow out of the cracks between the blocksbefore the surface bonding is applied. To avoidthis, specify that at least 85 percent of theparticles are to be retained on a No. 8 screen. Arectangular metal funnel can speed up fillingthe cores and avoid wasting the insulation (fig.19). It can be made by any sheet-metal shop tofit the width of the wall.

A n 8-inch thick wall made of surface-bonded, lightweight blocks with insulated coreshas a heat transmission resistance, R, of 5.8 oran overall U coefficient for the web in anS-inch-thick block of 0.273. In cold climates,where the design temperature is -10” F, conden-sation will likely form on the interior blocksurface at the web when the relative humidityin the house reaches 60 percent. Insulation, inaddition to the core type, will be needed inseverely cold climates. An insulation board andan interior finish may be applied to the wallwith an adhesive. Furring strips may be nailedto the wall, blanket or batt insulation appliedbetween strips, and an interior finish attached.

Installing the Plate

Saw strips of l/2-inch-thick, asphalt-impreg-nated fiberboard the same width as the blockwall. The fiberboard will conform to the top ofthe blocks in the wall and seal against wind andrain.

Drill holes in the fiberboard and wood plateat the proper places for the tie-down rods and

Figure 19.-Filling cores of concrete block wall withpellet insulation. Rectangular metal funnel made tofit the width of the wall reduces the filling time andavoids spillage.

electrical cables. Insert the rods and cablesthrough these holes, and place a washer andnut on each rod. Tighten each nut firmly, butnot with excessive pressure. Allow the concretefoundation or floor slab to cure at least 7 daysbefore tightening the nuts. Often the forms areleft on for a week. By the time the walls arestacked, the concrete will have cured enough sothat the nuts can be tightened before thesurface bonding is applied.

BASEMENT CONSTRUCTION

Surface-bonded concrete block walls arehighly water resistant and are therefore excel-lent for basement construction. Surface bond-ing eliminates the cement plastering (pargeting)required on the outside of ordinary mortar-joint walls. In some locations the foundationbelow ground tends to be unstable because ofvery wet spots or soil variations ranging fromrock to wet clay. In these situations theapplication of asphalt and plastic flim over the

12

surface bonding may provide added safetyagainst water leakage if the wall cracks.

The below-ground depth of nonreinforcedsurface-bonded basement walls should notexceed the FHA minimum property standardsgiven on page 4 . For greater depths belowground, add vertical reinforcing in concrete-filled block cores or increase the wall thicknessas required by FHA or by the building codeapplying to the particular locality.

OTHER CONSTRUCTION DETAILS

Pilasters

Pilasters built into the wall, intersectingpartition walls, and comer walls furnish lateralsupport in a long horizontal span. Pilasters aregenerally needed to support heavily loadedcenter beams in a building.

The construction and spacing of pilastersfor surface-bonded concrete block walls is thesame as for standard mortar-joint construction

(fig. 20). The horizontal spacing is usually 18times the thickness of the wall.

Beams or Joists

Beams, or joists, that are supported bysurface-bonded block walls must have a bearingof at least 3 inches on solid masonry (fig. 21).When the solid masonry is precast, the sectionsshould be bedded in mortar on the supportingblock beneath.

I/lOth THE D ISTANCEBETWEEN SUPPORTS

Figure 20.-A typical pilaster for strengthening a wall or supporting a beam.

13

4” BLOCK

I” RIGIDINSULATION

PRECAST ORCAST- IN-PLACES O L I D MASONRS

Figure 21.-Supporting joist, or beam, in a surface-bonded wall. Reinforce block cores beneath beam with steel

rods and concrete as required by building code.

SURFACE BONDING THE WALLS

Commercial Surface Bonding Premixes

Dry, premixed surface bonding is now beingpackaged by a number of firms and is availableon the retail market. Building material dealers,concrete products plants, and paint stores willbe stocking these products as they becomemore widely used. The bag sizes range from 25to 80 pounds. Some premixes require only theaddition of water. Others have a small plasticenvelope filled with calcium chloride inside thebag. The calcium chloride should be mixedwith water before making the wet mix. Somepremixes contain sand and should be appliedone-eighth inch thick. Those without sand needbe applied only one-sixteenth inch thick.Follow the manufacturer’s directions on thepackage.

The price of commercial premixes may runas much as three times the cost of ingredients

14

for home mixing. However, the commercialproducts are accurately proportioned andeliminate most of the labor of mixing. Theyalso eliminate the need to locate ingredients,some of which are sold only in large quantities.

Inspect the premix before using it to be surethat the fibers are well distributed; if they arenot, remix. Also, inspect for frayed glassstrands. If there is a large amount of frayedstrands in several of the packages, do notaccept the commercial premix. It will bedifficult to mix and apply. Try to get packagesfrom a different batch, as manufacturers areexperimenting to get proper control in mixingtheir product.

Remix as little as possible. Too muchmixing frays the strands or separates thestrands into individual filaments. This makesproper application of the bonding mix diffi-cult.

Ingredients for Home-Mixed Surface Bonding Ingredient

The ingredients for home-mixed surfacebonding are as follows:

Cement . . . , . . . . . . . . . ‘78 19 l/2

Lime . . . . . . . . . . . . . . . 15 3 314l Portland cement (normally packaged in

94-pound sacks). White cement is more expen-sive than regular gray cement but is lessalkaline, has a more finished appearance, andneeds less mineral coloring for pastel shades ifyou desire to color the mix. It is preferred for

all uses, but regular type- I gray cem-ebb%sometimes used.

Calcium stearate . . . . . .

Glass Fiber . . . . . . . . . . 4 1

Calcium chloride . . . . . .

Total . . . . . . . . . . . 100 25l Hydrated lime (normally packaged in

50-pound sacks). Hydrated lime makes themixture more workable and easier to apply.Lime with lowest alkaline content is madefrom pure dolomitic limestone.

l Calcium chloride (normally packaged inlOO-pound sacks), in flake or crystal form.Calcium chloride makes the mixture set upquicker and results in a harder surface. It isavailable from agricultural chemical dealers andfrom distri@tors handling it for ice and snowremoval.

Mix-in dry form-the cement, lime, andcalcium stearate thoroughly. Add the glassfiber and remix only long enough to distributethe fibers well. Too much stirring tends tobreak up the strands into individual filaments.When this happens, the bonding mix is hard toapply.

l Calcium stearate (normally packaged in50-pound boxes). Calcium stearate makes themix waterproof. Use a wettable technicalgrade, generally available from chemical distri-butors.

If mortar or concrete coloring is to be used,blend it into the dry mixture of cement, lime,and calcium stearate before the fibers areadded. Dark colors are not recommendedbecause they tend to splotch and fade. Evenwith light colors, weigh each batch carefully toavoid differences in color tone from batch tobatch.

l Glass fiber filament chopped into onehalf-inch lengths (normally packaged in 40- or50-pound boxes). Type E fiber, coated withsilane or chrome organic binder, is availablefrom plastic and chemical supply distributors.An alkali-resistant fiber, type K, may beavailable from building material dealers andplastic products dealers. The glass fiber acts asreinforcement in the mixture to give it strengthand prevent cracking.

Mix the calcium chloride with 1 gallon ofwater. Add this solution slowly to the dryingredients and mix thoroughly. Add aboutone-half gallon more of water. You may needto adjust this amount of water slightly toproduce the right consistency for good trowel-ing. The mix should have a creamy consis-tencyas thin as possible but not too thin toprevent handling with a trowel. Most peopletend to make it too stiff. It will then be hard toapply and may not bond properly.

Home Mixing the Materials

The bonding mix sets rapidly after thewater and calcium chloride have been added tothe dry ingredients, especially in hot weather.If one person is plastering, prepare only 25pounds of bonding mix at one time.

The weights of the ingredients needed tomake a 25-pound batch (dry weight) of thebonding mix are as follow,s:

Mixing can be done by hand in a wheel-barrow or small mortar box. A garden culti-vator rake or weeding hoe (three- or four-tine)works best. Check the mix with your hands forlumps. Wear rubber gloves to avoid possibleburning of the skin.

A power-driven plasterer’s mixer can beused (fig. 22). Put the water-calcium chloridesolution in the mixer first and add the dry mixslowly .

If the mix becomes too stiff before it can becompletely used, add a small amount of water.Do not add water more than 30 minutes after

Parts Pounds

1 114

2 l/2

15

Figure 22.-Motor-driven plasterer’s mixer for mixingsmall batches of surface bonding. The cylindricalmetal container rotates against a rubber or plasticblade, creating a scraping action that does not causethe fibers to “ball up” as with other types ofmixers.

the initial mixing because it weakens the bond.Discard such remixed batches whenever thematerial again becomes too stiff to apply on awet wall.

Batches of the dry ingredients can be mixedwell in advance so that there will be no delay inpreparing the mix when it is time to begin thebonding operation. If the dry mix is to bestored several weeks, place each batch in aplastic or multiwall paper bag and close the toptightly. Weigh out the calcium chloride foreach batch and seal it in a separate plastic bag;do not mix it with the dry ingredients.

Applying the Bonding Mix

Surface-bond both sides of the wall. It willnot be strong enough if the bonding mix isapplied on only one side.

The blocks must be free of dirt, loose sand,cement, and paint. If necessary, clean theblocks with a wire brush when they are dry.

Spray the wall with water until it is wet butnot dripping.

Work the mix from a hawk onto the wall

with a plasterer’s trowel (fig. 23). Hold thehawk against the wall to avoid excessive spillingof the mix.

A very thin coatabout one-sixteenth inchthick-of the bonding mix is all that is neces-Sary.

Work from the top of the wall downward.Thus, if the uncoated portion of the wall needsrewetting, the water will not run over freshlyapplied bonding.

Most workers can cover a section about 5feet wide standing in one position. Startapplying the bonding 2 or 3 feet from the topof the wall and trowel the mix upward to theplate. Move down another 2 or 3 feet andrepeat the process, blending the freshly coveredsection into the bottom of the section above.

There are four essential steps in successfullyapplying and finishing the bonding:

1. Apply the mix with firm trowel pressure,pushing the load upward and outwardunt i l a fa i r ly uniform coverage isattained.

2. Follow with longer, lighter strokes, hold-ing the face of the trowel at a very slightangle to the surface (about 5”) to even up

Figure 23.-Work the bonding mix from a hawk ontothe wall with a plasterer’s trowel. Note the speciallymade hawk with turned-up edges on three sides toprevent spilling the relatively thin mix.

c:fl

:

fcCl

0

acon

tillCC

b#

16

the plastered area and to spread excessbonding mix to fringe areas.

3. Move to the area below and apply mix as

4.

in steps 1 and 2. Continue bonding for 15to 20 minutes, or until you have covered25 to 30 square feet of surface.Dip the trowel in water to clean it.Retrowel the first area, holding thetrowel at a slight angle as in step 2. Withfirm pressure and long strokes, sweepover the area only enough to smooth outany unevenness.

TOO much retroweling may cause hairlinecracks, or crazing. In addition, a slightlyfibrous texture has a more pleasing appearanceand hides unevenness in the surface better thandoes a very smooth surface.

A calcamine brush may be used to obtain apleasing, brush surface in place of the trowelingdescribed in step 4. Brushing must be donewith light strokes immediately following step3, before the mix begins to set. In hot, dryweather brushing may need to be done onsmaller areas immediately after step 2. Useeither horizontal or vertical strokes dependingon the surface effect desired. When the brushbegins to drag because of mix collecting in thebristles, dip the brush in water and shake outthe excess. This will probably have to be doneafter brushing an area of 10 or 15 square feet.

A stippled surface may be obtained with apaint roller from which the fibers have beenburned off with a torch. The fibers melt,leaving nubs on the roller surface. Follow thesame procedure as described for obtaining abrushed surface.

If the bonding application must be stoppedfor 30 to 45 minutes or more, try to stop at acorner or at the edge of a window or dooropening, particularly when color has beenadded to the mix. Color differences that mightoccur between batches will then be less appa-rent.

Fill in the corner junction between the walland footing, carrying the bonding mix onto thetop of the footing on both sides of the wall (asillustrated in fig. 20). If the wall is built on aconcrete slab floor on grade, carry the surfacebonding down over the outside edge of the slabto help seal the joint between wall and floor(previously indicated in fig. 5).

Wet the finished bonding with a fine sprayof water once or twice the first day to aidcuring.

Roof construction can begin 24 hours afterthe bonding is completed, but a longer waitingperiod is desirable. Erecting the roof beforeapplying the surface bonding is advisablebecause interior work can be done duringinclement weather. Also, the added weight ofthe roof helps to seat blocks in the wall firmly.

Coverage of the Bonding Mix

Twenty-five pounds (dry weight) of bond-ing mix should cover at least 60 square feet ofwall, or about 30 square feet of wall bonded onboth sides.

Time Requirements

The time required to erect and completesurface-bonded walls will depend on suchfactors as the levelness of the floor or founda-tion on which the walls are to be erected, thebuilding experience and skill of the workers,the quality of the concrete blocks (particularlyuniformity of dimensions), and the buildingdesign-specifically, the number of window anddoor openings and offsets in the walls whichinvolve interior corners. However, a conserva-tive average would be 5.0 man-hours per 100blocks for stacking and 2.5 man-hours per 100blocks for surface bonding.

Sanded Bonding Mix

If a sanded surface is desired, add 1 part ofsand by weight to 1 part of regular bondingmix (dry weight). This must be applied one-eighth inch thick to give adequate strength andwaterproofing. The cost will be slightly higherthan the unsanded formulation previously des-cribed. Use a clean white sand such as that soldfor playpens; about 100 percent should pass aNo. 10 screen and 75 percent should pass a No.20 screen. The same amount of water is neededfor 50 pounds of sanded mix as for 25 poundsof unsanded mix.

17

PAINTING SURFACE-BONDED WALLS

Surface-bonded walls are easy to paint. Paints developed especially for use onAlthough not required for waterproofing pur- masonry are recommended for painting sur-poses (except in swimming pools and in tanks face-bonded walls. Usually these paints have aover 4 feet deep), painting can be used to latex base and are thinned with water. Theimprove the appearance of badly soiled walls or acrylic-type latex base is best, especially forto change the color scheme. exterior use.

I CAUTION

Surface bonding has been thoroughly tested as a construction techniquefor erecting block walls without mortar joints. However, because of thecomparative newness of surface bonding, the requirements, standards, andspecifications for its use are still evolving. The materials and proceduresrecommended in this publication are not necessarily in compliance with allFederal Government specifications on the use of surface bonding inFederally approved housing. This applies to housing financed or approved bythe Farmers Home Administration, the Federal Housing Administration, theVeterans Administration, and other government agencies. Prospectiveapplicants for Federal assistance should carefully examine the requirementsof the lending agency as they pertain to surface bonding.

I I

U.S. GOVERNMENT PRINTING OFFICE : 1976 o-207-707

Washington, D.C. Issued October 1974

1 8

For sale by the Superintendent of Documents, U.S. Government Printing ORiceWashington, D.C. 20402 - Price 45 cents

25% discount allowed on orders of 100 or more to one address

Stock No.OO1-tXO-O3340-9/Catalog No. A 1.75:374

There is a minimum charge of $1.00 for each mail order