I live in an East Coast row-house built in the early 1920s. There is a 3" crack in the solid brick party wall that I need to address (see photos). My neighbor's baby's room is on the other side and her crying comes right through.

Before readers freak out, some background:

My house was built later the neighbors house, and my house sticks out further in the back. Above the first floor, the bricks of the two houses are not interlocked--that is, there are two brick walls side to side with nothing connecting them. The back yards also slope down steeply. So it is no big surprise that this huge crack formed. I had the house underpinned when I moved in about 15 years ago so the movement has mostly stopped. But the crack expands and contracts slightly through the year, probably due to temperature changes. I monitor it in the attic and it moves about 3 mm a year--it's smallest in the spring, and largest in the fall.

I have now uncovered the crack (there was wire mesh and plaster over it the last 15 years) and need to decide how to fill it. I am thinking cut bricks and concrete. Because the crack is at its largest width right now, hopefully having solid material in there will help stop the movement.

But I'm also a little worried that when the brick walls want to come together 3 mm in the spring and there is a huge amount of pressure between the two wall sections (in the previously open gap), cracks will appear somewhere else, or the walls will twist or something.

If my question makes any sense at all, I'd welcome advice on the best way to fill the crack (or whether it is better to fill it with something flexible?).

Also: Is hydraulic cement better than concrete to put between the bricks?

enter image description here

  • In your 1st paragraph you say “see photos”. I see one. Are there more? It would be nice to see the extent of the crack. Can you move the cardboard and provide a picture at the top? (What is lying inside the crack?) – Lee Sam Oct 11 '20 at 22:15
  • Orientation? Is this looking from the inside of the your house? Does the crack “jog” where your house extends beyond your neighbor’s house? – Lee Sam Oct 11 '20 at 22:20
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    Cracks are caused by movement. You indicate that the crack “changes” depending on the season. No matter what, I’d recommend using a flexible filler/ cover to help eliminate future damage to your wall or to your neighbor’s wall. If you do something to your wall that causes damage to your neighbor’s wall, you will be responsible for repair, including consequential damage. – Lee Sam Oct 11 '20 at 22:33
  • Sorry, photo. There are cracks from the basement to the attic, but just one crack from 2nd floor up. So the crack does jog. Photo taken from inside my 2nd floor hallway; neighbors drywall visible on other side. That is a brick in the opening. Why should the filler material be flexible? I am considering flexible but thought solid material might stop the seasonal movement. – JCK Oct 11 '20 at 23:20

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