Making lime mortar

with Natural Hydraulic Limes

Small mixers

  1. Put in 1/2 of the required sand
  2. Add all of the lime.
  3. Mix well until the colour is uniform (about 2 minutes)
  4. Add the remaining sand. Mix well again (1-2 minutes)
  5. Continue mixing, adding water slowly, until the required plasticity or workability is achieved (approx. 10 minutes).

Larger mixers

  1. Introduce equal parts of the required sand.
  2. Add equal part of lime
  3. Add more sand (in equal part)
  4. Mix dry for a few of minutes until a homogenous mix is obtained. Continue mixing whilst slowly adding water until workable (approx. 10 minutes) The best results are achieved by adding water slowly. The mortar should be more like a dough than a slurry. The longer the mixing time, the more workable the mortar will be.

A small amount of lime putty can be added (max. 10% of the weight of the NHL binder). Do not add putty when working with NHL 2. Putty is added to achieve immediate workability and to reduce the mixing time. It is not necessary and is left to the user’s preference. If putty is incorporated, it should be done before the water is added; putty already contains water and adding it when the mix is complete will produce an unsatisfactory mortar that is too wet. Adding putty, even within the maximum % stated above, will reduce the strength of the mortar (see Mortar Tests).

Use standard buckets, always levelled. Once full, tap on the side to ensure that contents settle and fill to level. Dose at the volumes agreed with the supplier (1:1.5, 1:2 etc./ NHL: Sand). With the correct aggregates and dosages, mortars from Class II to Class IV are easily produced (from 10 to 2 N/mm2) by using NHL 5, NHL 3.5 and NHL 2 (see also individual product data sheets).

All St. Astier Natural Hydraulic Lime mortar can be reworked for up to 24 hours (see individual product data sheets). This is due to the absence of cement and gypsum in the lime and the minimal quantities of aluminates.

Reworking reduces waste; lime mortar can be prepared and left overnight so that a quick start can be made in the morning.

When preparing a natural hydraulic lime mortar for later use, place it on a board after mix and cover it to avoid contact with rain or sun. When re-mixing lime mortar, add the least possible water (in some cases it is not necessary to add any). The craftsman must rely on his judgment.

More on Lime Mortar for Restoration and Conservation.