The Constructor

How to Improve Masonry Resistance Against Penetration of Water?

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Masonry resistance against water penetration depends on materials used, types of wall, and quality of workmanship. Methods to improve water penetration resistance of masonry is discussed. There are number of methods by which the masonry water penetration resistance can be further increased. These methods, which are explained in this article, can be categorized into two major groups which are methods related to masonry design and methods related to masonry construction.

Fig.1: Masonry Structure

Methods to Improve Masonry Resistance Against Water Penetration

Methods Related to Design and Specifications of Masonry

It is advised to select and design type of a wall that is suitable for the degree of forced rain severity anticipated in the location of the project. Completely grouted barrier wall or drainage wall with minimum thickness of 20 mm is recommended for seriously driven rain condition.

Design of Drainage Wall to Improve Water Penetration Resistance of Masonry

When drainage wall is selected, the wall should be designed in such a way that prevents the water penetration through the outer Wythe of the wall. For the outer Wythe masonry wall maintain its water resistance ability, cracks under service load should be prevented. When masonry cement is employed, the lower tensile bond strength of the cement should be considered in specifying whether the veneer will crack or not whereas if steel studs are utilized it is recommended to consider the steel flexibility in determining whether the veneer cracks or not. The sealant of the outer Wythe joint must be specified carefully to prevent rainwater penetration through joints.

Fig.2: Drainage Masonry Wall

Cavity walls Design to Improve Masonry Water Penetration Resistance

If the cavity wall is determined to be employed, the design needs to be carried out to maintain the wall open and drained successfully. Appropriate flashing and weep holes must be determined to drain water out of the wall cavity in the case it enters the wall cavity. Masonry wall cavity should be kept clean by employing a board to remove mortar debris and 50 mm is advised to be used for the cavity width. Interstitial condensation must be avoided within the inner Wythe and this may be obtained by vapor barrier on the exterior face of interior Wythe. Either stainless steel or hot dip galvanized ties is recommended to apply.

Fig.3: Cavity Masonry Wall

Design and Detail Consideration to Make Rooms for Differential Movements

The following considerations are recommended to be considered to further increase the water penetration resistance of the masonry wall: a) Clay masonry walls commonly expand because of moisture and freezing and thawing. Therefore, expansion joints which are directed horizontally need to be installed. The location of these joints in the clay masonry walls are recommended to be under shelf angles whereas concrete masonry walls shrinks which is opposite to clay masonry. It is demonstrated that, the joint under the shelf should not be less than 3.65 mm because it is anticipated such gap is possible to be closed completely during the service life of the wall. This joint distance should be double because the size of the most of sealant is decreased by 50%. Finally, the veneer is likely to buckle, crack, and spall unless adequate joint is provided. b) Vertical expansion joint should be built at corners of clay masonry walls to prevent cracks. if the clay masonry walls are fixed close to the angle of the building, the wall expansion generate moments near the angle and eventually initiate cracks which compromise the water penetration resistance of the wall. c) The bond between clay masonry and concrete slabs, roofs, and foundation should be prevented because concrete shrinkage and expansion of clay masonry form differential strain that leads to cracks in the foundation if the bond between concrete elements and clay masonry is not broken. d) Shrinkage at concrete masonry openings such as doors and windows must be accommodated by introducing control joints at the openings to avoid tensile stress generation. e) When brick and block masonry wall is selected, the influence of restricted differential movement on wall deformation must be considered

Construction Methods to Improve Masonry Water Penetration Resistance

Compatible mortar and clay masonry units should be laid together. The mortar mix design and batching must be conducted properly. Initially, it is the best practice to blend cementitious ingredients with a portion of sand and a portion of water otherwise the ingredients will not combine adequately and the mixture will be too fluid. Therefore, the blending steps provided by ASTM C780 should be employed. Prior to first masonry layer installation, the foundation should be washed and cleaned thoroughly and the masonry unit must be placed immediately after the mortar bed is spread, and excessive masonry unit tapping is not allowed. Full head and bed joints shall be applied and raked joints should be employed for interior masonry. Mortar workability need to be kept at required level through retempering and it is not permissible to utilize mortar after 2 hours from initial blending. It is advised to damp wall masonry to help the curing of mortar. Read More: Masonry Reinforcement and Accessory Metals for Masonry Wall Construction
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