Building limes come in many forms: lime putty, hydrated lime, formulated lime, hot lime and natural hydraulic lime. It’s therefore no surprise that these choices of lime can cause confusion for specifiers, contractors and home owners!
We aim to demystify the topic and provide the necessary guidance so you can make the right choices when it comes to: lime binders, selection of the correct sands and provide information on correct mixes……..it’s not all about natural hydraulic lime!
Natural hydraulic lime or NHL, comes from limestone that has natural impurities of clay and other minerals.
There are three European classifications: NHL 2, NHL 3.5 and NHL 5 based on the compressive strength of laboratory mortars after 28 days. These are often somewhat misleadingly termed feebly hydraulic, moderately hydraulic and eminently hydraulic.
The strength of a hydraulic lime mortar can vary depending on the manufacturer of the lime and country of origin. Some NHL will test higher in the qualifying band, and some will test lower. HLM will also vary depending on the ratio of lime binder to aggregate and the type of aggregate or sand used.
Unlike lime putty which is ‘non-hydraulic’, natural hydraulic lime can set in damp conditions (indeed it requires water for a minimum period of around 72 hours to gain strength).
Use natural hydraulic lime where the need for breathability and flexibility is outweighed by the need for strength. Examples of work where you may select NHL are wall copings, chimneys and for floors. In some circumstances you may use hydraulic lime for rendering or plastering.
Our All About NHL page provides a wealth of information.
For more information and other products for traditional buildings please go to our main website.
Please e-mail us or call our technical sales team if you require further information or would like to purchase materials.