Design - Where is it appropriate to use NHL2 render and mortar?

Where is it appropriate to use NHL2 render and mortar?

NHL2 is Natural Hydraulic Lime with the lowest compressive strength in the banding of NHL2, NHL3.5 and NHL5.

NHL2 is suitable for most rendering jobs and can be used for external pointing where circumstances require a faster setting, less porous material than a non-hydraulic lime putty mortar.

In many areas of the UK, including locally in Wales, historic mortars fall somewhere between today’s fat limes and NHL2 in terms of their strength, porosity, flexibility and capillarity. Crucially NHL2 is more flexible and vapour permeable than NHL3.5 while still having a hydraulic set.

In reality, most NHL2 mixes reach a compressive strength which falls within the banding of an NHL3.5 (and an NHL3.5 reaches strengths of an NHL5).

When we are looking at using NHL it is often not useful to look at compressive strengths but it is very important to consider flexibility, porosity and capillarity.

In many circumstances NHL3.5 is inappropriate and it is often used too frequently in general specifications.

NHL2 mixes are used successfully in renders up and down the country and increasingly plasterers are using these as a default, reserving the use of NHL3.5 for only exceptional cases.