Masonry Magazine January 2006 Page. 26
LIME MORTAR
brick unit. Although older brick is quite weatherproof, this sacrificial type of mortar allows the brick to suffer the abuse caused by the elements and stand a better chance of being preserved.
Finally, lime mortars are cleaner to work with, as a result of being plastic and more workable, and their appearance and color blend harmoniously with a mortar of the same composition. In contrast, common cement-based mortars produce a grisly result on older structures.
Certainly, the work could be made easier, and consequently cheaper, by using a Type K mortar comprised of sand, lime and white Portland cement; however, the better option is to use only a lime and sand mortar on buildings that have been constructed using such materials.
Tips and Tricks
WHEN TACKLING A JOB that requires a straight lime-sand mixture, some experience at the very least, some caution - is preferred. If the correct application method is not followed, the mortar could soon fail, literally turning to powder.
First, the wall must be kept damp for several days after the lime-sand mortar is applied so that the carbonation process has the necessary time to start before the wall is allowed to dry out. As mentioned earlier, lime mortars can appear to have set. If you are tricked by this and allow the mortar to dry too quickly, it will not have fully started its reaction with carbon dioxide present in the air. With a lack of moisture causing an abbreviated carbonation process, the lime mortar will be so weak that harsh winter conditions could be sufficient enough to make it fall out as early as within the first year.
As I've suggested throughout this article, a straight lime and sand mixture takes a much longer time to set. To accelerate the set and increase its durability in exposed locations, you can add pozzolanic additives to lime mortar.
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24 Masonry
January 2006
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