Building Design and Construction Handbook - Merritt - Ventech!

11.22 SECTION ELEVEN
saturation. While the masonry is still very damp but with no water showing, the
joints should be repointed with a suitable mortar. This mortar may have a somewhat
stiff consistency to enable it to be tightly packed into place, and it may be ‘‘prehydrated’’
by standing for 1 or 2 hr before retempering and using. Pre-hydration is
said to stabilize the plasticity and workability of the mortar and to reduce the
shrinkage of the mortar after its application to the joints.
After repointing, the masonry should be kept in a damp condition for 2 or 3
days. If the brick are highly absorptive, they may contain a sufficient amount of
water to aid materially in curing.
Weathering and permeability tests described in C. C. Fishburn, ‘‘Effect of Outdoor
Exposure on the Water Permeability of Masonry Walls,’’ National Bureau of
Standards BMS Report 76 indicate that repointing of the face joints in permeable
brick masonry walls was the most effective and durable of all the remedial treatments
against leakage that did not change the appearance of the masonry.
Joints are grouted by scrubbing a thin coating of a grout over the joints in the
masonry. The grout may consist of equal parts by volume of portland cement and
fine sand, the sand passing a No.30 sieve.
The masonry should be thoroughly wetted and in a damp condition when the
grout is applied. The grout should be of the consistency of a heavy cream and
should be scrubbed into the joints with a stiff bristle brush, particularly into the
juncture between brick and mortar. The apparent width of the joint is slightly increased
by some staining of the brick with grout at the joint line. Excess grout may
be removed from smooth-textured brick with a damp sponge, before the grout
hardens. Care should be taken not to remove grout from between the edges of the
brick and the mortar joints. If the bricks are rough-textured, staining may be controlled
by the use of a template or by masking the bricks with paper masking tape.
Bond of the grout to the joints is better for ‘‘cut’’ or flush joints than for tooled
joints. If the joints have been tooled, they should preferably not be grouted until
after sufficient weathering has occurred to remove the film of cementing materials
from the joint surface, exposing the sand aggregate.
Grouting of the joints has been tried in the field and found to be effective on
leaky brick walls. The treatment is not so durable and water-resistant as a repointing
job but is much less expensive than repointing. Some tests of the water resistance
of grouted joints in brick masonry test walls are described in National Bureau of
Standards BMS Report 76.
The cost of either repointing or grouting the joints in brick masonry walls probably
greatly exceeds the cost of the additional labor and supervision needed to
make the walls water-resistant when built.
11.8 MASONRY-THICKNESS REQUIREMENTS
Walls should not vary in thickness between lateral supports. When it is necessary
to change thickness between floor levels to meet minimum-thickness requirements,
the greater thickness should be carried up to the next floor level.
Where walls of masonry hollow units or bonded hollow walls are decreased in
thickness, a course of solid masonry should be interposed between the wall below
and the thinner wall above, or else special units or construction should be used to
transmit the loads between the walls of different thickness.
The following limits on dimensions of masonry walls should be observed unless
the walls are designed for reinforcement, by application of engineering principles: