Expert: Dan Griffin - 9/18/2008

Question
Hello, I have a question regarding a special type of mortar.  I have a project where we are renovating a old brownstone building in Mahattan and the mortar that I have to do interior pointing  on does not match the same mortar
that was used when the building was first constructed.  Could you tell me of a recipe for a mortar that was used in the late 1800's for old brownstone buildings to doing interior work on.  If you can't send me a recipe, could you tell me of a place where I might found one.  Thank you

Answer
Panos, the color of mortar is very subject to the sand that is used, what is more critical is the compressive strength of the mortar.  If you  use any of todays Portland based mortars you may well destroy the bricks.  You need some professional advice, but the best source will be a masonry contractor in your area or a restoration specialist.  Portland cement would not have been used before 1850, even into the 1900s, and it would be harder than the bricks causing damage to the bricks with any movement.  I suspect your mortar was a lime mortar.  A common formula would be 1 part common lime to 3 parts sand.  The sand may have contained coarse to fine gradation unlike the mason's sand of today.

Here is an article about lime mortar:
http://en.wikipedia.org/wiki/Lime_mortar