I hope this is the correct category to post in.
I’m the newest owner of what may be the oldest apartment building in the country (built by Henre Shreve prior to 1815) South of Pittsburgh.
The walls are over a foot thick with outer, inner and internal layers of brick. Those on the outside and inside walls are in ok shape but randomly, within the walls, there are some bricks that have completely turned to red clay-like sand. It does seem to be water-related, as the worst parts are near where water would run down the facade. Also, the mortar joints are crumbling, allowing water infiltration.
The walls seem to be holding and there are very few signs of any cracking. I do plan to eventually repoint the whole building; slowly over time
My question is if I should fill the voids left behind from the crumbling internal bricks, or repoint and leave them alone.
My concern is that filling those voids with a harder mortar might end up cracking the external layers (think ice in a pothole).
My theory was to use a straight lime/sand mixture to fill these voids, allowing for a softer material than what surrounds it, at the price of longevity, of course.
Thoughts?
Feel free to google search 301 Front St, Brownsville PA
Replies
There are some excellent resources available from the National Parks Service about repairing and preserving historic masonry. They can be found for free here.
https://www.nps.gov/tps/how-to-preserve/briefs.htm
There are also many specialists that can give you advice - some of these for free. You might want to start with mortar/cement companies in your area.
Here are some general tips -
-The crumbling brick is likely softer common brick used on an interior wythe of the wall. sometimes brick used for interior wythes was much softer than exterior brick. This is not an issue until water comes into play..
-Strength of mortar is more important that properties of the brick. The mortar is the sacrificial element in these systems. As the building moves and shifts, the mortar should degrade not the brick.
-Weaker is better as far as mortar - Cement mortar on a historic brick wall can be disastrous.
-Try to find some historic brick that match your brick as close as possible (possibly from on site, possibly from another source) and replace brick as you repoint the wall. If you cannot find soft brick, new brick would likely be better than filling with mortar - but again, use weak mortar.
Beautiful building by the way. In that area there should be a ton of expertise on historic masonry and rehab (some of it free - especially if you are on the National Register of Historic Places).
Good luck with the project!
What an excellent and thorough answer. Thank you so much!
I would suggest Mike Haduck YouTube videos, as he is a mason in NE PA, and gives advice about bricks and mortar mixes based on the climate zone in which you live. He has many videos on repairing brick structures and adjusting mortar mixes so the hardness of the mortar matches with the brick being used...