How to Increase Resistance of Masonry to Water Penetration

Water penetration resistance of masonry depends on wall type, workmanship, and materials. In this section, additional information is presented on each of these.

1. Specification and design:

a. Specify and design wall types appropriate for the severity of driving rain expected in the geographic location of the building. In areas of severe driving rain, specify a drainage wall or a fully grouted barrier wall with a thickness of at least 8 in.

b. If a drainage wall is specified, specify and design to reduce water penetration through the outer wythe. (1) Dont let the outer wythe crack under service loads. If masonry cement is used, consider the effect of its lower tensile bond strength in determining whether the veneer will crack. If steel studs are used, consider the effect of their flexibility in determining whether the veneer will crack. Follow industry recommendations that the out-of-plane deflection of the studs not exceed their span divided by 600. (2) Specify proper sealant joints in outer wythe.

c. If a cavity wall is specified, specify and design to keep the cavity open and properly drained.
(1) Specify proper weepholes and flashing to keep water out of cavity and direct it outward if it gets in.
(2) Specify hot-dip galvanized or stainless-steel ties.
(3) Specify a cavity at least 2 in. wide. Keep the cavity clean by beveling the back of the joint, using a board to catch mortar droppings, or both.
(4) Use a vapor barrier on the exterior face of the interior wythe, to prevent interstitial condensation within the inner wythe

d. Design and detail to accommodate differential movement.

(1) Provide horizontally oriented expansion joints in clay masonry walls under shelf angles. Over time, clay masonry typically expands about 300 μe, due to permanent moisture expansion and freeze-thaw expansion. In contrast, concrete and concrete masonry shrink is typically about 600 μe. These opposite tendencies combine to produce differential strain of about 1000 μe over a 12-ft (144 in.) story height, that corresponds to a differential deformation of 0.144 in. In other words, a gap of 0.144 in. under a shelf angle would be expected to close completely during the life of a building. Because the gap must be filled with sealant that can compress to about half of its original thickness, the gap must be twice the 0.144 in., or 0.29 in. A gap of 3/8 in. is typically used. If a sufficient gap is not used, the veneer will be loaded vertically, and can spall, crack, or even buckle under the load.

(2) Provide vertically oriented expansion joints in clay masonry walls near corners. Expansion of clay masonry, restrained at building corners, causes moments about vertical axes near the corners. Vertically oriented expansion joints prevent such moments and resulting cracking.

(3) Use bond breaker between clay masonry walls and concrete foundations, slabs, and roofs. Expansion of clay masonry (about 300 μe) and shrinkage of concrete (about 600 μe) combine to give differential strain of 1000 μe. If restrained, this differential strain can crack the concrete foundation.

(4) Use control joints at door and window openings of concrete masonry walls. These will prevent tensile stresses from restrained shrinkage. (5) If composite brick-block masonry walls are used, consider the effect of restrained differential movement on interfacial stresses and wall deformations.

2. Construction:
a. Use compatible combinations of mortar and clay units. Clay units with high IRA should be wetted and used with highretentivity mortar.
b. Mix and batch mortar properly: Measure ingredients accurately by volume. To distribute them thoroughly in the mix, combine cementitious ingredients with part of the sand and part of the water. If all the water is added at the beginning, the initial mix will be too fluid, and the cementitious ingredients will again not combine well. The following mixing sequence is taken from ASTM C780 (field mortar):
Add all cement and lime + 1/2 sand + 3/4 water
Mix 2 min
Add remaining sand and water
Mix 3 to 8 min
c. Clean and roughen the foundation before laying the first course.
d. Lay units within 1 min of spreading the mortar bed.
e. Lay units without excessive tapping.
f. Use full bed and head joints.
g. Use concave-tooled joints. In particular, use raked joints for interior masonry only.
h. Retemper mortar as required to maintain workability. Do not use mortar more than 2-1/2 h after initial mixing.
i. After laying, keep masonry walls damp to help the mortar cure properly.


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