Updated: Mar 6
Natural Hydraulic Lime (NHL) is a cement which is most aptly used in restoring and building masonry structures that require a lime-based mortar. Lime-based mortars are required when repointing or rebuilding older masonry structures which were built use NHL or when working with types of stones/bricks that will benefit from a lime-based mortar. For example, here at Lennox Masonry in Victoria, BC, we utilize NHL when restoring historical buildings which were built with limestone, sandstone, or clay bricks.
NHL comes in the following formats:
NHL 2 - This is the least hydraulic format that is currently produced, making it the most flexible lime cement out of the NHL options. This variety of natural hydraulic lime cements is best used when used for plastering, rendering, finishing, or while working with weaker stones such as lime and sandstone.
NHL 3.5 - This version is moderately hydraulic and is best used when working in colder climates that produce a freeze and thaw cycle such as North America. The 3.5 version is most notably used when repointing or rebuilding brick, stone, or terracotta masonry materials. It can also be used for making scratch coats and finishing coats for exterior stucco.
NHL 5 - Lastly, NHL 5 is incredibly hydraulic, making it the least workable lime cement out of all the other options. It is best served when pouring concrete foundations or footers, stone wall head copings, or when working with masonry structures that are subjected to water such as bridges.
The Cement Mixer Method:
This method is ideal when large amounts of mortar are required on a dependable basis. The only down-side to using Batch or Drum mixers is that they typically cause the mortar to 'ball-up', which will create additional labor, and the mortar will then have to be squished. This is caused by the paddles within the mixer itself. However, the following steps will help to reduce this problem.
Before mixing the mortar, it is important to measure out the Natural Hydraulic Lime and sand of choice by volume. In this example we'll use a bucket. It's important that each mix is as consistent as possible. Measuring the materials with a shovel may cause the volume of each load to differ.
1. It is important to start with a dry and empty mixer. In order for the lime and sand to thoroughly mix together, they need to blend without the addition of water.
2. Measure out the chosen sand to lime ratio — this will depend on the grade of Natural Hydraulic Lime being used and its intended application.
3. Add the sand to the mixer.
4. Add the lime to the mixer.
5. Start the mixer and allow the materials to mix for at least several minutes before adding water.
6. Stop the mixer and let the materials settle for 5-10 minutes.
7. Start the mixer again and begin adding small amounts of water until the desired consistency is obtained. When pouring water into the mixer, allow it to mix for a minute or so before adding more. Adding too much water will only weaken the final mixture, making it unstable. Introduce just enough water for the chemical processes to take place, so that the lime and sand properly bond. A mix which resembles a hardy pizza dough is ideal.
8. Once an optimal mixture of sand to lime to water is obtained, allow it to rest for several minutes prior to briefly mixing it again.
9. Stop the mixer and let the mortar settle again before applying it.
If you would like to see some of our completed masonry and stonemasonry projects which used Natural Hydraulic Lime Mortar, please visit our Gallery and Current Projects pages. We are currently in the process of reconstructing 17th-Century Limestone Stonework, involving Gothic Cathedral features at the Norfolk Heritage Lodge in Saanich, B.C., Canada.
If you have any questions, please visit our Contact Page to reach us. And don't forget to visit our Masonry Blog to find other articles pertaining to Masonry and Stonework.
Lennox Masonry of Victoria, B.C., specializes in traditional stonework, heritage restoration, historical masonry, and creative masonry projects. If you are interested in obtaining a unique work of art in the medium of stone and masonry, please Contact us today.