Type O/K Mortar

Hydrated lime has already been slaked. Type N or 'normal' hydrated lime need only be putty overnight. Type S the same. I no longer have ready access to the ASTMs. If you do, C-207 used to cover hydrated lime. I am sure some currently active masons may arrive to help.

With regard to mortar, Type O seems best for very low compressive strength interior applications. Would not a Type S mortar be better for tuck pointing an exterior foundation? It is sticky and flexible. Type S - 1 cubic foot Portland cement, 1/2 cubic foot lime, and ~ 4+ cubic foot sand. I think the ASTM for mortar is C-270. If you don't find hydrated lime, Type S can be made - 1/2 cubic foot Portland cement, 1 cubic foot masonry cement, and ~ 4 cubic foot sand.

My knowledge is dated. Changes in the last 20 years are not reflected in my comments. Do some small mixture proportions and make one inch cube test specimens. After they have cured, check them for strength, adhesion and flexibility. Select the mix that performs best. I would be specifying mortar that adheres well, resists freeze thaw,and flexes with the stone wall. Type S is where I would start.

I'ive done the make up the mortar by hand business... it wasn't all that bad. Type S line and water mixed to a putty... let sit a few weeks then mix 1-2.5 with sand. no cement. Time consuming but not hard.


however my house is 100 years older and the original mortar is straight lime. Your 1895 house probably does have some portland in the mix..

raiderfan said:

I was going to make a 1-2-10 mix (Type O, i think -- with the 2 being Type S Hydrated Lime). I forgot to mention that this was for sections of two interior basement walls, not exterior. The parts that i am looking to replace, have turned powdery and crumbling (from what I've read, its doing what it was designed to do).

Man.. Things would be easier if i could just mix up a bag of Type N from a hardware store and slap it on!! LOL!

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