Look, I See Lime Inclusions

The next time you come across a historic masonry building take a close look at the surface of the mortar joints. Yes, I know they often get over-looked in competition with the brick or stone, but trust me on this one.  The first thing you should notice is the sand. The sand is the largest part of the mortar by volume and is the material that gives the joint its color, texture and cohesiveness. The next thing you should notice is white specs or small chunks of carbonated lime putty. If this evidence is identified you’ve got yourself a truly historic lime putty mortar. No need to hire a fancy consultant or pay for an expensive mortar test, you can with confidence declare your finding.

Mortars that display lime inclusions were typically mixed using quicklime and sand mixed on the jobsite with a shovel or mixing hoe by hand and with a lot of hard work I might add. Often, the moisture would be added to the sand first then the quicklime added to the damp material. The quicklime would slake first into a hydrate of lime then into putty if more water was added to the mixture.

The batch of mortar would be tossed and turned until the masons yelled out “MUD!” then the material would find its way onto the laborers back then unloaded onto the boards. The mortar would be placed in the wall as construction proceeded. Mortar consistency might certainly vary from batch to batch with this serve as you go system in place. There might be a time when a laborer catches up with the demand for mortar and has more time to mix a particular batch-thus breaking up the lime inclusions into smaller pieces and even dissolving them altogether.

If it is your desire to match these inclusions you have a couple of options. Use a mortar mixture made from damp sand and quicklime (hot lime mortar mix- allow 24 hrs before use), or make lime inclusions from straight lime putty by allowing the material to air dry then running the harden pieces through a series of aggregate sieves to match the inclusion size you specify. Then simply add the inclusions to your lime putty mortar just before application taking care not to over mix. The inclusions in the image above were added to the masons hawk just before installation and were protected from the initial mixing of the lime putty and sand to keep them from breaking apart.

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  1. #1 by Neal Kwon on September 13, 2011 - 8:47 pm

    This blog is terrific. There’s always all the correct info at the guidelines of my fingers. Many thanks and keep up the great work!

  2. #2 by Marina on September 21, 2011 - 8:57 pm

    You have really interesting blog, keep up posting such informative posts!

  3. #3 by Traditional Lime Co Ireland www.traditionallime.com on September 23, 2011 - 5:26 pm

    Traditionally lime mortar was made by piling up 3 measures of as dug aggregate (horse cart,donkey cart,barrows) depending on the size of job
    This was arranged in a doughnut shape on the ground
    One measure of Quicklime was placed in the middle
    Water from barrels was thrown on top of the quicklime (by experience the mortar makers knew how much to use)
    As the quicklime reacted the aggregate was piled on top
    This pile was left to react and heat which dried out the aggregate and left you with a dry pile of lime and aggregate
    The pile was then mixed together which was easy as it was very dry
    The mix was then thrown tro a screen to remove the big aggregate and any unburned limestone
    The mix was then piled up and tamped down ready for use
    As needed an amount of mixed lime and aggregate was taken of the pile water added and mixed with a larry as required by the masons or plasterers
    This type of mix was used for all building and base coat plasters except in very cold weather or where the mix was required to flow eg grouting where a hot mix was used
    By this method the hydraulic properties of the lime was retained as all traditionally produced quicklime had some hydraulic set because of the fuel used
    Only specialist Lime Mortars were made using Putty eg Internal finishing, cornice work ,gauged brick,ashlar pointing, tuck pointing.
    The lime inclusions were the result of late slaking

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