Pozzolans are added to non-hydraulic lime mortar mixes to turn them in to FHL’s Formulated Hydraulic limes.
The greater the percentage of pozzolan to mortar is added the quicker and harder the set will become, this make it a very accurate way to be sure that the mortar strength doesn’t exceed the strength of the masonry, and that the porosity of the mortar remains greater than the masonry as well.
typical addition of pozzolans by volume
40:1 for a very weak hydraulic set, for when you want that little extra bite when pointing.
20:1 a feeble to moderate set, suits most general building purposes.
8:1 getting to a more eminatly set, works well for retaining walls, ridges, and below dpc level.