Hydraulic Limes (NHL)

Natural Hydraulic Limes (NHL's) are produced from limestone containing clay and other impurities which give a faster initial set in more extreme conditions (including underwater!). There are three strengths of hydraulic lime and are categorised as per table below, where the number refers to the compressive strength of the mortar after 28 days (please note the selection of aggregate and mix ratio will also affect the final strength):

• NHL2 - contains less than 12% clay which means it is slower to set;
• NHL3.5 - contains 12-18% clay which gives it a slightly faster set;
• NHL5 - has up to 25% clay content which means that a much faster set is achieved.

These limes have become increasingly popular over the last decade or so because of their comparative 'ease of use' and 'strength' compared to fat limes.