Publisher’s version / Version de l'éditeur:
Technical Note (National Research Council of Canada. Division of Building Research), 1954-06-15
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
NRC Publications Archive
Archives des publications du CNRC
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/20358832
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Building Weathertight Masonry Walls Above Grade
Dickens, H. B.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=5977267d-95d4-4ac2-8510-b7b558341695 https://publications-cnrc.canada.ca/fra/voir/objet/?id=5977267d-95d4-4ac2-8510-b7b558341695
DIVISION OF BUILDING RESEARCH
'f
E
C
1HIN II CAlL
NOTlE
164
NOT FOR PUBLICATION FOR INTERNAL USE
PREPARED BY H.B. Dickens CHECKED BY N.B.H. APPROVED BYR.F.L. PREPARED FOR General Inquiry Repl y ｾ June
15, 1954.
SUBJECT Building Weathertight Nasonry v.Jalls Above Grade
Dampness in ｾ｡ｳｯｮｲｹ walls may result from the leakage of drainage water from the roof and horizontal surfaces into the wall, the penetration of wind-driven rain through the wall, the condensation of moisture within or on the inside face of the wall, or the capillary rise of groundVJater from the foundation.
The best time to consider means of preventing dampness in masonry walls is during construction, by providing adequate flashing, by increasing the roof overhang if possible, by properly caulking and
sealing all cracks around doors, windows and window sills, by isolating ground moisture with a dampproof course and by providing good drainage facilities and suitable vapour protection. The correct procedures for
such measures are well established and are clearly detailed in many good reference books on building. If properly carried out they are effective in eliminating moisture penetration by these paths.
There still remains the possibility that water may penetrate the masonry itself through the mortar joints. It is this problem
that will be considered here.
:Hasonry Wall Studies
Studies have already been made on moisture penetration of masonry walls by several research organizations but much still
remains to be done before all contributory factors can be properly assessed. A summary of these previous investigations is given in Building Note No. 12 of this Division entitled "Some Aspects of the Problem of Moisture Penetration of Brick Masonry", a copy of which can be obtained on request. .
A review of these studies indicates the following factors as significant in determining the moisture resistance of masonry walls:
1. A full, intimate, and permanent bond between brick and mortar is necessary for watertightness of masonry walls
- 2
-2. Strength is not the criterion of mortar bond. The use of a relatively strong and dense mortar such as a rich cement mortar has often led to shrinkage cracks between the mortar and brick through which rain can readily penetrate;
3. The nature and extent of the bond developed between
brick and mortar is related to the suction properties of the brick and to the water retentivity of the
mortar. The initial rate of water absorption of the brick is a measure of suction•. Water retentivity
indicates the ability of the ｭｯｲｴｾｲ to retain the mixing water against the brick suction.
4.
Good workmanship is essential in obtaining a s'atisfac-tory job and is more Jikely to be achieved when using a mortar having good ｰｬ｡ｳｴｩ｣ｩｾｹ and workability. Both these properties of a mortar generally increase with an increase in lime content.Clay Masonr:l
The majority of the work carried out to date by the various research organizations has dealt with clay products and on this basis the following specific recommendations are suggested for building watertight clay masonry walls and should be applied
ｷｨ･ｲ･ｶ･ｾ practicable.
1. Control the rate of suction of the brick. Bricks of high suction can have their suction reduced to a
suitable level by wetting before laying. A rough test for determining if wetting is required may be made by sprinkling a few drops of water on the flat of the brick and noting the time of complete absorption. If this time exceeds one minute, wetting is not needed. A more precise method of determining brick suction has been established by the American Society for Testing Materials in their Specification C67-50-Sampling and Testing Brick; where possible the bricks used should have a rate of suction within the limits recommended in this specification.
2. Use only mortars with a lime content at least equal to the volume of cement. Suggested mortars would be:
1:1:6 and 1:2:8 or 9 cement:lime:sand (by volume). Such mortars generallY have high water retentivity, good plasticity and workability. When it is proposed to use unslaked lime, it should be slaked for a minimum of 7 days before using to ensure complete hydration. Hydrated lime should stand at least overnight.
3.
Make sure that full joints are obtained in both bed and head joints.(a) Mortar for the bed joint should be spread thick without furrows;
(b) Head joints can be filled by using plenty of mortar on the end of the brick and then pushing the brick into place so that the mortar oozes out at the top of the head joint. After the bricks are in place they should not be moved or tapped as this weakens the bond;
(c) Bricks with frogs should be laid with the frog up.
The United States National Bureau of Standards has shown that walls can be built having a high resistance to water penetration only when the bed joints and the head joints are.
completely filled with mortar.
4.
All mortar joints should be concave tooled as this will help in reducing the separation cracking between bricks and mortar. This should be done using a rounded tool slightly larger than the joint and with sufficient force to press the mortar tightly against the brick on both sides of the mortar joint.Concrete and Sand-lime Masonry
A major consideration in building watertight walls with concrete or sand-lime masonry is the relatively high degree of dimensional change likely to be exhibited by these units due to changes in their moisture content. This excessive movement is apt to result in shrinkage cracking more severe than is usually experienced with walls built of clay units.
The magnitude of the shrinkage varies with the type of product, the nature of the curing treatment, the age and the
dryness of the block. High pressure steam curing greatly reduces the amount of shrinkage that will take place with concrete units on the job but adds substantially to the cost of the unit.
Shrinkage can also be limited to some extent by correct proportioning and careful control during manufacture.
To further minimize drying shrinkage it is essential that concrete and sand-lime units be in a reasonably dry condition when placed in the wall. Unless it is known that concrete and sand-lime
units have been delivered in a properly cured and dried condition, arrangements should be made to stack them for as long a period as practicable (several weeks or months, if possible) under conditions
of good air circulation and protection from rain. Other things being equal, the greatest shrinkage may be expected from units laid
4
-Neither the Cenedian nor the United States specifications. for concrete end sand-lime masonry units set limits upon the drying
shrinkage of the units but limits have been imposed on the drying shrinkage of these products by the British Standard Specifications BS834-1944 (Concrete Blocks), BSl18o-1944 (Concrete Bricks), and BS187-1942 (Sand-lime Bricks). Where it is intended that labora-tory tests be made, the drying shrinkage should be determined in the manner detailed in these specifications and the units should meet the shrinkage requirements of the appropriate specification before being placed in the wall.
Where the design of building permits, cracking can also be controlled by dividing the wall into suitable lengths or panels by means of control joints, thus providing freedom from restraint at the ends. Reinforcement in the bed joints of brickwork or block construction is also useful but there is at present little information as to the amount of reinforcement necessary with units of given shrinkage.
The recommendations given in this note for clay masonry can also be usefully applied to construction in which concrete or sand-lime units are used with the possible exception of the requirement dealing with suction. In general, it is not desirable • to wet concrete or sand-lime units to reduce suction at the time
of laying as this may increase the subsequent shrinkage in the structure and may result in more serious cracking than would
otherwise occur. The more absorbent types of units sometimes have to be wetted at the time of laying to prevent too much water
being removed from the mortar but such 'Hetting should be kept to a minimum consistent with the adjustment of suction.
In view of the relatively high drying shrinkage likely to be exhibited by concrete and sand-lime products, it is recommen-ded that ｷｾｬｬｳ built of these units be laid with a mortar having a high lime content. Such mortars will allow greater movement of the masonry without cracking and, being weaker than the units, will avoid fracturing of the units themselves.
A suggested mortar mix would be:
1:2:8 or 9 cement:lime:sand (by volume). General
It is apparent that the requirements outlined here for
clay, concrete, and ｳ｡ｬｾｑＭｬｩｭ･ masonry can best be met in construction carried out during the 'summer months. During colder weather it
is undesirable to erect a wall u.singmat:er:i'al's that are relatively damp and thus ｴｨ･ｾｷ･ｴｴｩｮｧ of even clay wlits to reduce suction may have to be limitea when the temperature is low. Cold weather may also require a'mix richer in cement to be used to lessen the
possibility of the mortar freezing before setting. The following specifications cover materials used in masonry construction.
ｾ Specifications of the Canadian Standards Association
Available from the Canadian Standards Association, National Research B'uilding, Ottawa
A82.1-1954 - Building Brick (made from clay or shale) A82.)-1954 - Sand-lime Building Brick .. A82.4-1954 - Structural Clay Load-bearing Wall Tile A82.5-1954 - Structural Clay Non-load-bearing Tile A82.42-1950 - Quicklime for Structural Purposes A82.43-1950 - Hydrated Lime for Masonry Purposes A82.56-1950 - Aggregate for Masonry Mortar
A5 -1951 - Portland Cements
Specifications :of the American Society for Testing Materials Available from the American Society for Testing Materials, 1916 Race St., :Philade1phia 3, Pa.
C55-52 - Concrete Building Brick
C90-52 - Hollow Load-bearing Concrete Masonry Units Cl29-52 - Hollow Non-load-bearing Concrete Masonry Units C145-52 - Solid Load-bearing Concrete Masonry Units
