Cement, Lime, Sand Ratio for Repointing Stone Foundation

I have done a lot of reading and feel I have a good grasp on how to go about repointing my stone foundation. Only thing I can't nail down is the ratio of cement:sand:hydrated lime. A lot of opinions on this with varying ratios.

House is Pre 1900, not sure exactly how old though.

Looking for somebody to nail down the ratio.

Thanks in advance.

 

There is about a 90% chance that is a lime mortar if it is indeed pre-1910. Is it soft and very light in color?

 

It is soft and light in colour. Sorry for the late reply.

 

Then it is lime mortar. Using a modern portland cement mortar will cause the destruction of the wall in a relatively short period of time. It being lime mortar is not a bad thing, since lime mortars are cheaper and easier to work with, as well as being overall a better material to keep stones separated. I have answered this question in depth already and will search for the old posts and link tomorrow.

 

Much Appreciated.

 

The proper method is to take Type S dry lime, submerge it in water for at least 3 days (that means gently cover it with water and do not ever, ever stir it), keeping it covered with water at all times (that will create mature lime putty). After that, it will last for months, so long as it is kept covered with water and left alone. Only add sand and expose it to air when you are ready to use it, and only enough for the day's usage.

Straight lime mortar is 1:3 (lime putty/sand), by volume.

It doesn't hurt to gauge the mortar with portland cement (only because it is available) to assist with an inital set that allows for easier cleaning and tooling. The ratio is debatable, and will have to be determined on-site, but could range from 1:6:21 to 1:10:33 (cement/lime putty/sand), by volume.

 

Tscar, what does it mean, to "gauge" with Portland?

 

The problem with lime mortars is that they have an extremely slow hardening rate. Years, in fact, to reach ultimate strength. To provide for a quick initial set, material can be added to the mix that will NOT assist the lime to carbonate, but will provide a separate reaction that lends initial strength.

Only a small amount of material may be added or the physical properties of the lime mortar will be altered enough that it's advantages are negated.

That is the simple explanation, anyway.

 

Just for fun, some pics of abandoned lime kilns, also showing why you do not repair lime mortar with portland cement based mortars.

http://72.41.69.75/awlkilns.htm

 

@tscar - your pik link isnt working however I see and thank you for your advice here - my cousin is a mason and think that he only knows new construction as he told me to use a portland cement and sand ration to repoint as well as then skim coat my foundation wall right in front of where i want to hurry and then regrade and lay topsoil weed mat and mulch to plant on this house i have redone - can anyone help with the right ratio asap please my mortar is light and soft so i think it is the same scenario - why what will portland mixes do to a lime based foundation wall and how quick will it destroy it? i was told use half of a 94lb bag of portland cement and half of 50lbs quikrete sand then told 22 or 23 lbs to equal half ratio - then enrich w/ a shovel or two of portland cement - please help i see you ratio's and am a little perplexed - 1 to 3 ok but the rest is what? determined on-site, but could range from 1:6:21 to 1:10:33 (cement/lime putty/sand), by volume. and then how do i do it myself then if it has to be determined how and of what material -thanks tscar etc -

 

Strength is not the most imporant factor for mortar. - the key is compatibility and workability. - The ASTM morat specs also point this out in the specifications.

You can carry tremendous loads with sand lime mortar.

The newer hard bricks that are hard fired may be more compatible with sand-lime mortar, they will not be much better because the loads on most brick masonry are really pretty minor. That is the reason for the note in the specifications.

Dick

 

i am being told to use if not sand lime mortar to use 2 to 3 shovels of sand per portland cement - someone had said 1 for 1 and 2 cement per 1 sand - which is accurate and do i need to really dig out all the old mortar thoroughly - ? - thanks