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#1
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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-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. 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 enough, or is it exactly what *shouldn't* be used? http://www.finehomebuilding.com/how-...type-need.aspx says type N is 1 part Portland cement, 1 part lime and 6 parts sand. 1 part white Portland cement, 2 1/2 parts hydrated lime, and 5 to 6 parts sand http://www.sacredplaces.org/PSP-Info...%20Masonry.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 have to be formulated by hand? Should I insist that the mason uses that 1 : 2.5 : 5 ratio? Jimmy |
#2
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Low-cement mortar mix for historic brick
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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 -- dadiOH ____________________________ Winters getting colder? Tired of the rat race? Taxes out of hand? Maybe just ready for a change? Check it out... http://www.floridaloghouse.net |
#3
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Low-cement mortar mix for historic brick
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... 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. 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 enough, or is it exactly what *shouldn't* be used? http://www.finehomebuilding.com/how-...type-need.aspx says type N is 1 part Portland cement, 1 part lime and 6 parts sand. 1 part white Portland cement, 2 1/2 parts hydrated lime, and 5 to 6 parts sand http://www.sacredplaces.org/PSP-Info...%20Masonry.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 have to be formulated by hand? Should I insist that the mason uses that 1 : 2.5 : 5 ratio? Jimmy It all in the Sides of the Sand Hard Sand # 1 Medium Hard Sand # 2 Medium Soft Sand #3 Soft Sand # 4 |
#4
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Low-cement mortar mix for historic brick
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 |
#5
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Low-cement mortar mix for historic brick
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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? 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. ____________________ Do you have experience repointing historic bricks? None whatsoever. I just know what "soft" nortar refers to. -- dadiOH ____________________________ Winters getting colder? Tired of the rat race? Taxes out of hand? Maybe just ready for a change? Check it out... http://www.floridaloghouse.net |
#7
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Low-cement mortar mix for historic brick
dadiOH wrote:
wrote: 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? 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. 1870s. Best suggestion, follow the advice of your mason but have the specs in the contract so you can sue if he is wrong. I need to know what to ask for in the specs. In a few places, some mason did 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 correct mortar type. Jimmy |
#8
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Low-cement mortar mix for historic brick
On Fri, 02 Aug 2013 13:40:50 -0700, wrote:
...snip.... 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 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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