Using Lime Putty to Make Mortar
Mortar made with lime putty and sand, sometimes referred to as
roughage or course (coarse???) stuff, should be measured
by volume, and may require slightly different proportions from
those used with hydrated lime. No additional water is usually
needed to achieve a workable consistency because enough water
is already contained in the putty.
Sand is proportioned first, followed by the lime putty, then
mixed for five (5) minutes or until all the sand is thoroughly
coated with the lime putty.
But mixing, in the familiar sense of turning over with a hoe,
sometimes may not be sufficient if the best possible performance
is to be obtained from a lime putty mortar. Although the old practice
of chopping, beating and ramming the mortar has largely
been forgotten, recent field work has confirmed that lime putty
and sand rammed and beaten with a wooden mallet or ax handle,
interspersed by chopping with a hoe, can significantly improve
workability and performance. The intensity of this action increases
the overall lime/sand contact and removes any surplus water by
compacting the other ingredients. It may also be advantageous
for larger projects to use a mortar pan mill for mixing.
Mortar pan mills which have a long tradition in Europe produce
a superior lime putty mortar not attainable with today's modern
paddle and drum type mixers.
For larger repointing projects the lime putty and sand can be
mixed together ahead of time and stored indefinitely, on or off
site, which eliminates the need for piles of sand on the job site.
This mixture, which resembles damp brown sugar, must be protected
from the air in sealed containers with a wet piece of burlap over
the top or sealed in a large plastic bag to prevent evaporation
and premature carbonation. The lime putty and sand mixture can
be recombined into a workable plastic state months later with
no additional water.
If portland cement is specified in a lime putty and sand mortar
Type O (1:2:9) or Type K (1:3:11) the portland cement
should first be mixed into a slurry paste before adding it to
the lime putty and sand. Not only will this ensure that the portland
cement is evenly distributed throughout the mixture, but if dry
portland cement is added to wet ingredients it tends to "ball
up," jeopardizing dispersion. (Usually water must be added
to the lime putty and sand anyway once the portland cement is
Any color pigments should be added at this stage and mixed
for a full five minutes. The mortar should be used within 30 minutes
to 1-1ž2 hours and it should not be retempered. Once portland
cement has been added the mortar can no longer be stored.