19 June 2001
involved, a chimney may be needed on both sides of the wall or beam. In all
cases, the chimney should extend the full width of the hole.
c. Ensure forms are constructed so that pressure can be applied to
the chimney cap at the proper time.
d. Ensure forms are mortar tight at all joints between adjacent
sections, between the forms and concrete, and at the tie-bolt holes to prevent the
loss of mortar when pressure is applied to the concrete during the final states of
placement. Place twisted or stranded caulking cotton, folded canvas strips, or
similar material between the joints as the forms are built.
e. Keep concrete surfaces wet for several hours, preferably overnight,
f. Before placing the front section of form for each lift, coat the
surface of the old concrete with a 3-mm (118 mils) thick layer of mortar. This
mortar should have the same sand and cement content and the same water-
cement ratio as the new concrete. The surface should be damp, but not wet. The
mortar can be applied with an air-suction gun, brush, or rubbed into the surface
by hand. (Be sure worker is wearing rubber gloves if doing by hand.)
g. Place concrete immediately. Ensure thorough compaction by
vibration or pressure grouting to 0.1 MPa (14.5 psi) .
h. Remove forms the day after placement. If chimneys were used,
remove the remaining projections the second day working up from the bottom.
i. Thoroughly moist-cure the new concrete.
j Finish with a wood float. Tool or chamfer edges and corners as
required. Avoid using water in finishing.