dadiOH wrote:
wrote:
Our house from the 1870s has some places in its brick
foundation where the mortar has deteriorated.

Everything I read, such as
http://www.nps.gov/tps/how-to-preser...tar-joints.htm
, says it's very important to use a soft mortar with soft
historic bricks. And that when masons use modern hard
mortars with a high Portland cement content, it
eventually damages the bricks. But I've had trouble
finding out what exactly this soft mortar should be.

Depending on the age, lime mortar.
http://en.wikipedia.org/wiki/Lime_mortar

More...
http://construction.about.com/od/Mas...rtar-Types.htm

Thanks for the post, but it doesn't really answer my questions.

Are you suggesting a lime mortar with no cement? That contradicts the info at sacredplaces.org, which recommends a small amount of cement in the mixture. And the wikipedia article doesn't say what specifications I should require from a mason.

I know about the specifications for types M, S, N, O, and K mortar. My question was, is the correct mortar for historic brick one of those types, or something totally different?

Do you have experience repointing historic bricks?

Jimmy