Edison Coatings custom-matched and produced NHL 5 repointing mortar for historic Belvedere Castle in New York's Central Park.
Natural Hydraulic Lime, or "NHL" is a traditional material which combines some of the characteristics of ordinary lime with the more positive, through-setting characteristics of cement. It is produced by burning limestone that has naturally-occuring clay or silica impurities and then slaking to produce a fine powder.
NHL 2.0, 3.5, 5.0
Natural Hydraulic Limes are classified by the strength they achieve after 28 days' cure. The levels of silica and/or clay impurities in the original limestone determine how much of the cement component is formed during firing, as opposed to lime, and this determines ultimate strength.
NHL 2.0 achieves a minimum compressive strength of 2 MPa (290 psi) in 28 days. Ordinary, non-hydraulic dolomitic limes available throughout the United States and Canada may produce similar strengths.
NHL 3.5 achieves a minimum of 3.5 MPa (~508 psi).
NHL 5 achieves a minimum compressive strength of 5 MPa (725 psi).
These classifications are based on MINIMUM requirements for specific standard mixes cured under controlled conditions. Actual strengths achieved may differ significantly, and all NHL's exceed the minimum required strengths.
HISTORY OF USE
Natural Hydraulic Limes (NHL) have been produced and used extensively in Europe for centuries. British Engineer John Smeaton, whose work in the 1750's clarified the role of clay impurities in the formation of cement-like compounds, is generally credited with having opened the door to engineered uses of both NHL and Natural Cement.
NHL was well-known in North America, but was never intentionally produced on any significant scale here, despite the abundance of suitable raw materials.
Large quantities were imported, however, primarily for use in light colored, non-staining mortars for marble and limestone in the period preceeding the introduction of low-alkali white portland cements in the early 20th Century.
Today, NHL's are most frequently used as replacement mortars, when specifications focus more on specific performance parameters rather than on replication of an original mix design. They are also used in green construction, as they have less impact on the environment, in terms of their lower energy usage for production, compared to modern cements.
Natural Hydraulic Lime (NHL) 2.0, 3.5 and 5.0 are designed for use in mortars and plasters for historical building restoration, quality
building/construction and green building. The products have CE Certifications and are in full compliance with UNI EN 459 1:2010.
By properly selecting aggregates and proportions, it is possible to produce mortar mixes ranging from 2.6 MPa to 5.1 MPa (380-740 psi) at 28 days with NHL 3.5, making it the most versatile of Natural Hydraulic Limes.
Pre-mixed, ready-to-use mortars are also available as BioMix 35.
NHL 5.0 will produce harder mortars, and provide better resistance to harsher, higher moisture exposures. They can also be a suitable analog for early portland cement mortars, which are poorly replicated with modern cements. Pre-mixed, ready-to-use mortars are also available as BioMix 50.