The preliminary hardening of high-lime content mortars
those mortars that contain more lime by volume than portland cement,
i.e., Type O (1:2:9), Type K (1:3:11), and straight lime/sand,
Type "L" (0:1:3) takes place fairly rapidly as
water in the mix is lost to the porous surface of the masonry
and through evaporation.
A high-lime mortar (especially Type "L") left to dry
out too rapidly can result in chalking, poor adhesion, and poor
Periodic wetting of the repointed area after the mortar joints
are thumb-print hard and have been finish tooled may significantly
accelerate the carbonation process.
When feasible, misting using a hand sprayer with a fine nozzle
can be simple to do for a day or two after repointing. Local conditions
will dictate the frequency of wetting, but initially it may be
as often as every hour and gradually reduced to every three or
Walls should be covered with burlap for the first three
days after repointing. (Plastic may be used, but it should
be tented out and not placed directly against the wall.) This
helps keep the walls damp and protects them from direct sunlight.
Once carbonation of the lime has begun, it will continue for
many years and the lime will gain strength as it reverts back
to calcium carbonate within the wall.