Lafarge NHL 3.5 is a moderately hydraulic lime produced in France. This NHL 3.5 is the whitest NHL 3.5 we are aware of… Almost as white as office paper and about as white as Type S or High Calcium Lime (lime without the ability to set). NHL 3.5 is typically used for pointing historic brick or other porous masonry such as limestone, sandstone or schist. It is fairly resistant to freeze-thaw cycles but also maintains high vapor permeability and flexural strength making it a good all-around repair mortar for porous masonry materials.
NHL 3.5 is also being used in many types of sustainable, green construction including straw bale construction as an exterior and interior plaster or stucco or mixed with hemp to create hempcrete. But because each manufacturer produces a unique Natural Hydraulic Lime product based on the geology of the area it is quarried, it is important to test the product before generalizing its appropriateness.
We have found that NHL 3.5 is not great for very hard masonry units including hard-fired bricks. The reason for this is that Lafarge NHL 3.5, in particular, contains more free lime (non-hydraulic lime), and it can leach out of the masonry and slightly stain the bricks. While this isn’t going to cause irreversible damage it is unsightly and therefore a harder natural hydraulic lime such as NHL 5 is recommended for non-porous masonry structures.
Lafarge has a long and strong track record of producing Natural Hydraulic Lime stretching back to the mid 1800s. Since this time over 200 million bags (25kg) have been manufactured and used for a wide range of projects from renovating churches and castles to new build construction.
It is of high quality and manufactured from specially selected limestone containing clay and other impurities. This enables the material to set without exposure to air and even under water.