Ensuring that a replacement mortar will be sympathetic to historic masonry is key to a successful repointing project, so replacement mortar should be more vapor permeable and lower strength than the original mortar and the masonry units. The goal is to make sure that the new mortar is a sacrificial element, meaning that it will slowly deteriorate and can be periodically replaced. This deterioration occurs because the mortar, rather than the masonry units, is handling the stress of building movement and moisture. Mortar should be breathable enough to transfer moisture out of the wall system and flexible enough to absorb the pressure of freeze-thaw cycles and building movement.
Available Lime Mortar Products
Choose a product below to view specifications and details.
Maintain Hydraulic Lime Products
Hydraulic lime is chemically very similar to nonhydraulic lime but it contains impurities, called pozzolans, that allow it to set in two stages: the first set is when water is added, and the second occurs as the mortar is exposed to the atmosphere. The first set is important, since it allows the mortar to attain strength more quickly and to cure in wet conditions.
Hydraulic lime is available in two forms: Natural Hydraulic Lime (NHL) and Pozzolanic Hydraulic Lime (PHL). Both are sold as dry bagged products.
Both NHL and PHL mortars are flexible and breathable enough for historic restoration, and they are durable enough for the extreme conditions.
- Available as untinted, unsanded binder
- Offered in 51 exclusive Centurywerks colors (link to kit colors)
- Fine, mason, and coarse sands (link to sieve reports)
- Fully custom paste and/or aggregate matching available
- Extensive in-house color library for fast track matching
Maintain Saint Astier® NHL
Saint Astier® NHL is the world’s premium natural hydraulic lime and has been in production for over 150 years.
Hydraulicity for St. Astier lime is achieved by the nature of the raw material, which is mined from a uniform and undisturbed layer of calcareous rock infiltrated mainly by silica with only insignificant traces of other elements. “Hydraulicity” means that the mortar has its initial set with water, much like cement, and a second set by absorption of carbon dioxide. This accelerates the set time and provides earlier strength than hydrated lime, so it is a more durable product.
NHL is not produced domestically so all NHL products are imported to the United States from Europe, and we selected St. Astier for its consistent, time-honored, and rigorously tested products.
St. Astier NHL offers three categories of lime with different compressive strengths to choose from. Hydraulic limes are categorized as Feebly Hydraulic (2.0), Moderately Hydraulic (3.5), and Eminently Hydraulic (5.0). These classifications originated from the European Norm EN-459, which requires that the NHL 2.0 have a minimum strength of 2MPa; the 3.5 a minimum strength of 3.5MPa; and the NHL 5.0 a minimum strength of 5.0MPa. The acceptable compressive strength parameters according to EN 459 are:
2.0 — Feebly Hydraulic (322-1015 PSI)
3.5 — Moderately Hydraulic (507-1450 PSI)
5.0 — Eminently Hydraulic (725 – 2175 PSI)
EN 459 also provides a standard for a minimum amount of free lime, which is important for workability, autogenous healing of microcracks, and elasticity. Free lime also contributes to the final strength and it provides some tolerance for initial structural movements and both sufficient strength and plasticity to accept slight load shifts. The higher the free lime, the more accommodating the mortar:
Minimum Free Lime (%) under EN-459
NHL 2.0 >35%
NHL 3.5 >25%
NHL 5.0 >15%
- Suitable for building and plastering mortars, grouts, injection, lime concrete and paints.
- Provides flexibility, which minimizes shrinkage and cracking and allows for minor movements.
- Highly vapor permeable and is very effective at moving moisture out of the wall system, reducing moisture in walls improving insulation levels.
- Excellent salt resistance makes it suitable for marine environments.
- Outstanding weather resistance: early setting means earlier protection from adverse weather.
- Long lasting alkalinity resists bacterial and algae growth.
Maintain PHL
PHL is a manufactured lime mortars, so pozzolans are added in a controlled factory environment. PHL contains no portland cement, and is a breathable and flexible mortar that is suitable for repointing, laying, and building with friable masonry units. PHL reaches an earlier initial strength at approximately seven days (versus 28 days for NHL) so it requires less extended curing protections and allows installers to extend the season into colder weather.
Maintain PHL complies with ASTM C1707 “Standard Specification for Pozzolanic Hydraulic Lime for Structural Purposes” and is manufactured in our Chicago facility to our strict quality control standards.
- ASTM C1707 Standard Specification for Pozzolanic Hydraulic Lime for Structural Purposes
- ASTM C1713 Standard Specification for Mortars for the Repair of Historic Masonry
- ASTM Standard Specification for Preblended Dry Mortar Mix for Unit Masonry.
- ASTM 144 Standard Specification for Aggregate for Masonry Mortar
- Preservation Brief #2 “Repointing Mortar Joints in Historic Masonry Buildings”
- EN459 “Building Lime. Definition, Standards and Conformity Criteria.”
Need Assistance?
Contact us at 773-598-4300 for more information and assistance.
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