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Thanks for bringing up this very interesting Topic of Discussion.

Some inputs

1. Yes, it is true that cement works with a proportion of sand / quarry dust in mud mortar mix, low clay content/ non-clayey soil may also be tested. The idea is to achieve good stabilization. Sometimes where cement is not available, locally produces lime is an alternative for stabilisation; I checked the possibilities in some locations in Nepal where they were actually producing lime (chunna).

2. Organic fibres reinforcement is also a good idea, especially fibres from hemp that has a natural protective coating against easy decay in dry conditions would be good as mortar reinforcement (provided the mortar mix is stabilized and compact). Alternatively the wire mesh is also suggested as horizontal mortar band reinforcement at regular intervals by some architects/ organisations. Personally I like it as a very good solution given the easy trans-portability or wire mesh rolls to remote locations. (Though I am not sure about the vertical inserts- reinforcement bars as the same can be very easily deformed with the impact in heavy stone masonry mass, if not integrated with sufficient concreting around bars to keep is stiff?)

More important than a good mortar mix is the “bonding” that may not be compromised, even a dry stone masonry may perform stable and safe if the bonding are proportionate and well structured (Key elements) for corners, for distributing spans and for tying the structures/ walls together (this is evident from the post earthquake findings), Nevertheless stabilized mortar is highly recommended. (I would really suggest we refer to some to Lauri Baker's studies made after Chamoli earthquake on stone masonry.)

Stabilized Mud Mortar Reference: Here is an extract from NBC 204, which I found very useful as a reference.

Preparation of Stabilised Mud Mortar

i. Collect three cubic metres of mud which contains 40 to 50 % sand and 60 to 50 % of clay.

ii. Mix 180 kg of chopped wheat or paddy straw with the mud. The wheat straw has to be chopped in 20 mm lengths, whereas rice straw may be up to 50 mm in length. Old straw is preferred to fresh straw. Pour water over it and kneed until the straw and mud becomes an uniform paste.

iii. Kneed three to four times a day until the straw decomposes. The mix should not be allowed to dry during this process. It takes generally seven days in summer and 14 days in winter to decompose the straw. iv. The stabilised mud mortar is then ready.

……(if we don’t have 14 days then cement is the quicker solution)…