Trying to save some fieldstone masonry, and while there are recipies for the mortar there are too many variations from less than trusted sources. So am looking for something that doesn’t take weeks to make
A non putty lime mix is typically 1 to 3
1 part natural hydraulic lime ( NHL 2 or 3.5)
3 parts well graded sand.
How I remember it explained to me , many years ago, was well graded sand has a mix of aggragate sizes in it. The space between the dry aggragate is called the void ratio. It’s that void you need to fill with the NHL. Well graded sand “”typically”” has a 33% void ratio so that’s how to determine the 1 to 3 mix.
“Builders” sand is not a good choice, you want the mix of agggragete sizes. And being finer and mostly uniform it drops the void ratio way down and you can toss that rule of thumb 1 to 3 mix out the window.
I don’t know about the putty mix except it’s like making the starter for sour dough bread LOL
I’d use moderate, NHL 3.5 at a ration of 3 parts sand : 1 part lime. You will need to ‘wet’ the wall first to make a key or else things dry too quickly & continue to wet occasionally after you have done the work. Over wetting will wash out the pointing. You are encouraging the crystallisation in the wetting process which is in effect the hardening. It takes three or more days for the process to start & this is what makes modern builders worried in that they don’t believe the mortar will ever set!