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 delivers either.
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.