Gradings of hydraulic lime?

[michael]

When refering to the various grades of Hydraulic lime i.e hl1 hl2 hl3 etc which end of the scale is weak hydraulic lime and which end is strong?

 

[skier-hughes]

NHL 2 sets to 2 newtons in 28 days, 3.5 to 3.5 newtons and 5 to 5 newtons in 28 days, so the higher the number the strnger it is.

I wonder if nhl2 when left for 56 days gets any stronger?

 

[MdB]

From here: http://en.wikipedia.org/wiki/Lime_mortar

There are three strength grades for Natural Hydraulic Lime (NHL): 2, 3.5 and 5. These are termed feebly hydraulic, moderately hydraulic and eminently hydraulic

 

[biffvernon]

Natural Hydraulic Limes are currently classified according to 3 European grades:

Natural Hydraulic Lime 2, abbreviated NHL2, Natural Hydraulic Lime 3.5 (NHL3.5) and the third is (NHL5).

These grades are based upon the strengths the materials achieve in standard laboratory tests, so the higher the number the greater the strength. However each grade can have a minimum and maximum figure and to make matters more confusing the maximum figure for one grade can be higher than the minimum of the next grade up. In other words the grades overlap.

The hydraulic limes given above are produced from naturally occurring limestones. It is possible however to achieve similar results by mixing suitable materials and in this case the materials can only be classified as Hydraulic Limes abbreviated HL. Lastly it may be necessary to add additional pozzolanic material to increase the strength of an existing NHL2 (or 3.5 or 5). In this case a Z is added. Eg NHL3.5Z
This information is contained in a British / European Standard, BSEN 459 Part 1 2001 including quality control regime for testing.

Singleton Birch also make a NHL1, which is not included in EN 459, but is probably quite close to the strength of much of the lime used in 18th and 19th century London.

Singleton Birch, the only British NHL producer, have a very informative website here:
http://www.naturalhydrauliclime.com/

 

[dze]

From what I have read about NHL 2, 3.5, 5 the figures refer to the minimum strength at 28 days. Also apparently the range for a NHL 2 is from 2 upto 7 so this one product could also be a 3.5 and even a 5 :? :?

 

[Gervase]

Most NHL5 limes (the dolomitic ones) are nearer 10N compressive strength after a month, so the bandings are very much minimum spec rather than average.