Custom Lime Cement
One of the biggest and most common mistakes that plague the
restoration of vintage masonry structures is the use of incompatible modern materials
and particularly portland based cements and mortars in their repairs.
Portland cement wasn’t commercially available until around
1875 and wasn’t until about the beginning of the 20th century that
it replaced lime putty cement based mortars almost completely. Introducing portland cement based mortars
into the historic fabric of a historic masonry building more often than not
results in rapid deterioration of the original material, as they are not nearly
hard enough to be compatible with portland cements and mortars.
Many original substrates are already delicate if not
unstable to begin with. Introducing portland
cements and mortars places these fragile materials, such as soft stone, terra
cotta and brick in a position to almost certainly fail and deteriorate.
The main reason for this is that lime putty cement was
deemed obsolete during the early 20th century and the technology for
manufacture and use was nearly completely forgotten. Only in the past 20 years or so has it been
reestablished as valuable and relevant in the masonry industry. Using lime mortars is totally different than
using portland mortars. Special care and
skill is required when building/restoring with lime putty mortars, unlike
portland cement based mortars which can often be installed and forgotten, lime
putty mortars must be properly prepared, installed and tended to for several
days, and often much longer to achieve a proper cure and to retain its proper
color and important physical properties and characteristics.
It is as important to hire a contractor with years of
experience with these special materials as it is to use them when they are
appropriate, perhaps even more important!
If these materials are not used and tended properly the project is
doomed to failure.
It’s important to consult an experienced expert before the
project begins. The common first mistake
in restoration specification development is to be lead astray by a sales
representative of counter clerk who is in the business of selling modern
materials. These folks usually know
their products well enough but rarely know anything about the fragility and
critical physical properties of vintage building materials. The result is nearly always recommending
inappropriate materials and techniques.
They often know only what ‘so-and-so’ contractor buys and uses so it
must be right. Right? WRONG!
With all due respect, most sales reps and counter clerks
have no experience in this field and they are not interested in studying and
gaining the knowledge and experience required to really understand the issues
at play in the first place. They sell
modern materials at a nice markup and if they have any questions they have
recourse to the factory technicians who know as little about restoration with
authentic materials as they do. It’s
just not their field of expertise and they sell modern materials. It’s really only rarely that modern materials
are justified. Usually the answer is
repairing the structure in like means and materials used for the original
construction. These materials are
compatible by nature and the restoration is an authentic, organic process that
is both seamlessly beautiful and durable; using modern materials rarely
Liszt Historical Restoration has been manufacturing lime
putty for our own use for over 15 years.
Our skilled craftsmen have been using it for many years insuring
consistency and performance in our restoration projects.