Page 502 - Forensic Structural Engineering Handbook

MASONRY STRUCTURES 13.47

Tuck-pointing, stucco, or two coats of brush-applied water-cement paint greatly reduce
water permeance. The only effective and durable methods of reducing water permeance of
brick walls without significantly changing their appearance is by tuck-pointing, grout injec-
tion, and replacement of deteriorated and displaced bricks.

Grout Injection
Proper functional performance of masonry walls requires solidly filled bed and head joints.
Seismically damaged masonry walls and those with void mortar joints have been success-
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fully repaired by pressure injection of fine, cement-based grout. Binda provides technical
background and guidelines for repair of masonry walls by grout injection. Project specifi-
cations for grout injection should include preinjection masonry evaluation; environmental
requirements; grout materials, delivery, storage, handling, proportioning, batching, mixing,
and testing; surface repairs; injection holes; grout injection; and cleanup.

Tuck-Pointing

Tuck-pointing of mortar joints is appropriate when joints are severely deteriorated. It is a
process of cutting out old mortar to a uniform depth and placing new mortar in the joint.
Employ only qualified and experienced tuck-pointing craftsmen. An individual who is an
excellent bricklayer may not be a good tuck-pointing craftsman.
A tuck-pointing trial is advisable. In an inconspicuous area cut out 10 linear ft (3.048 m)
of cracked mortar joints. Use hand tools or a pneumatic angle grinder to wet-cut joints to a
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uniform depth of / 4 in (19 mm). Remove debris from the joint with water. Use of electric
grinders to dry-cut joints will produce potentially harmful silica dust and is not recommended.
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Tuck-point with Specifications for Mortar for Unit Masonry, C 270, type N mortar in
accordance with appendix X3 of that standard. Prehydrate tuck-pointing mortar as follows:
Carefully measure and record the amount and origin of each dry ingredient. Thoroughly
mix all dry ingredients. Add only enough clean water to the dry mix to produce a damp,
workable consistency, which will retain its shape when formed into a ball. Let mortar stand
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in this dampened condition for 1 to 1 / 2 hours. Dampen cut joints, but leave no standing
water in the joint. Add water to prehydrated mortar to bring it to a workable consistency
but somewhat drier than conventional mortar. Pack mortar tightly into joints in thin layers
of not more than 14 in (6 mm). Allow each layer to become “thumbprint-hard” before
applying the next layer. After the last layer of mortar is thumbprint-hard, tool joints to
match the profile of the original joints.
Let trial tuck-pointed joints stand for two weeks of dry weather. Compare the color of
tuck-pointed joints with that of adjacent original mortar joints. If the color difference is not
acceptable to the owner, adjust the mortar dry ingredients and repeat the trial tuck-pointing
process until the color difference is acceptable. When acceptance is obtained, use the final
trial mix of dry ingredients to tuck-point all cracked mortar joints.

Coatings
Clear coatings for masonry typically do not bridge cracks and, therefore, do not prevent
water permeance in masonry, although they may temporarily reduce it. This writer does not
recommend clear coatings on brick masonry. 25
Reference 50 discusses paint coatings for masonry. Two coats of water cement paint are
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inexpensive and effective. Stucco application is described in ACI and ASTM publications.
Stain coatings to solve color problems are described by Suprenant. 55