Low-cement mortar mix for historic brick

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-preserve/briefs/2- repoint-mortar-joints.htm , says it's very important to use a soft mortar w ith soft historic bricks. And that when masons use modern hard mortars wit h a high Portland cement content, it eventually damages the bricks. But I' ve had trouble finding out what exactly this soft mortar should be.
One mason told me he'd use type N mortar (750 psi) for this project, rather than the type S (1800 psi) he'd use on modern bricks. Is type N soft enou gh, or is it exactly what *shouldn't* be used?
http://www.finehomebuilding.com/how-to/articles/mortar-what-type-need.aspx says type N is 1 part Portland cement, 1 part lime and 6 parts sand. 1 par t white Portland cement, 2 1/2 parts hydrated lime, and 5 to 6 parts sand
http://www.sacredplaces.org/PSP-InfoClearingHouse/articles/Repointing%20Mas onry.htm says 1 part white Portland cement, 2 1/2 parts hydrated lime, and 5 to 6 parts sand is recommended for 19th century row houses in NYC.
Is there a commercially available mortar for historic bricks, or does it ha ve to be formulated by hand? Should I insist that the mason uses that 1 : 2.5 : 5 ratio?
Jimmy
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Depending on the age, lime mortar. http://en.wikipedia.org/wiki/Lime_mortar
More... http://construction.about.com/od/Masonry/a/Mortar-Mix-Mortar-Types.htm
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dadiOH
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dadiOH wrote:

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
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And I repeat, how old are they? Lots of buildings were stuck together with lime mortar, I have no idea if yours was or not.
Best suggestion, follow the advice of your mason but have the specs in the contract so you can sue if he is wrong. ____________________

None whatsoever. I just know what "soft" nortar refers to.
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dadiOH wrote:

1870s.

I need to know what to ask for in the specs. In a few places, some mason d id inappropriate work in the past -- modern high-cement mortar (it "pings" when you drop a chunk of it, and you can't scrape it with your fingernail). So I don't want to just leave it to a mason without specifying the correc t mortar type.
Jimmy
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Contact local, or nearby City's Historical Society. Large cities have some very skilled, knowledgeable people who will help with your question. Also, I've had no trouble reaching people at the Smithsonian in Washington, DC. who either told me how to do something myself, had me send items to them for repair, or provided a LONG list of recommended/approved 'repairers'
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It all in the Sides of the Sand
Hard Sand # 1 Medium Hard Sand # 2 Medium Soft Sand #3 Soft Sand # 4
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On Fri, 2 Aug 2013 08:40:44 -0700 (PDT), snipped-for-privacy@mailinator.com wrote:

Maybe you can viist or track down by phone or web, the masons who work at Colonial Williamsburg Va. or some place like that. I think the buildings there are original. Yes, some are original although some are from 1699 to 1780. Maybe that's too old?) Or maybe locally there is even one brick building from the period, that is owned by the local historical society. Or maybe the historical society where you are or in a big city has a mason who knows about this.
Any big brick building from the period that is in good condition might lead you to someone who really knows what he's talking about. Most people will talk to you for free. Especially at 4PM.
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