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I just inspected the interior foundation walls in my 1920s house and found this horizontal crack behind a closet. At the widest part, the crack is about 1.5 cm. There is what seems to be an intentional bevel in the wall right above where the crack is (above that, the wall is masonry blocks, a little thinner than below, hence the bevel). Also, the lower part of the wall is out of plumb. The gas main runs vertically along it. At the bottom, there is 6 cm between the gas main. At the middle where the crack is, there is old parge coat that dried while contacting both the gas main and the wall, which makes it seem it has been this way for some time.

overall view of crack closer view of crack closeup of contact point with gas main

I am not sure if the crack has grown or shifted. I bought the house a couple of years ago. I marked and dated the ends of the crack and drew perpendicular lines across it so that I can check it for any changes in the future.

Is this serious enough to take some kind of action now, or should I just keep monitoring it?

Update 5/31/17 Here's a piece that easily chipped off, showing the layers in more detail.

chip that came off the wall

I'm not sure if that chip is just part of the parge coat or if it contains part of the foundation itself. I started to remove the parge coat, but I wasn't sure if I should keep going.

Update 6/4/17

I chiseled away at the parge coat. I started in the wide horizontal crack and chiseled up to where the masonry blocks were (below that, the foundation wall is concrete). I revealed a section that exposed the masonry block.

revealed section of masonry block

I chiseled down again from there. I used a small pry bar and wedged one end of it down underneath the parge coat, with the tip flush with the masonry block. When I pried it out, it pulled off two large sections of parge coat that were bonded with what seemed to be the concrete. It pulled off some large stones and revealed some gaps in the concrete that went farther toward the outside of the house than the masonry block.

masonry block with gaps in concrete below

Here are some profile shots showing the depth of the gaps in the concrete that resulted.

profile of the concrete, showing gas main

profile of the concrete, looking away from gas main.

Also, I carefully chiseled the parge coat behind the gas main, which had been bonding the gas main to the foundation wall, and I found that when I created a gap between the gas main and the foundation wall, the gas main sprung back toward the wall about .5 - 1 centimeter, indicating that the gas main had been pushed in a bit from the wall.

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    I asked a question about a different looking crack in my 1920s home and got some good answers which might be helpful. – StrongBad Jun 2 '17 at 14:40
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Vertical foundation wall cracks are probably "expansion or contraction" cracks...not structural cracks. Horizontal foundation wall cracks are probably structural cracks (failure cracks). Both are caused by lack of reinforcing steel (rebars) and / or thickness and strength of concrete.

If the crack "steps" up the wall, it could be caused from settlement of the footings.

I doubt anything is imminent. In order to determine the severity of the situation, we'll monitor the crack for a year or so...

Monitoring means measuring the width and length of the crack. In order to do this, you'll need to remove all material over the crack along the length of the crack. However, before you start such an undertaking, you need to determine if it's necessary to deconstruct the surface of the wall, (I.e.: how long has it been there, how long are you going to be there, etc.) If you monitor the crack, measure everything on a regular basis (weekly) and write it down.

Note: If you determine the wall is failing, you may need to fix it or disclose the possible wall failure when you go to sell your house, under the real estate disclosure laws.

  • Thanks. I started to chip off what I thought was the parge coat, as shown in the bottom picture, but I wasn't sure if I was chipping off part of the foundation wall itself. Can you tell from the bottom picture whether that chip is just parge coat and it's safe to keep chipping away? – Mike Eng Jun 2 '17 at 2:02
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    Hmmm...I can't tell what the material is you're removing nor what is behind it. Does the wall seem to be decomposing? Can you dig into the wall with a screwdriver? – Lee Sam Jun 2 '17 at 3:52
  • Thanks again. The wall didn't seem to be decomposing, and I couldn't dig into it (easily) with a screwdriver. I kept digging and updated the question with what I found. Turns out the foundation wall is concrete with masonry blocks stacked on top of it. I'm guessing what I revealed in the concrete foundation wall needs some professional help. What is your assessment? – Mike Eng Jun 4 '17 at 18:53
  • Yes, I'd check with either a structural engineer (not a civil engineer) or an architect. I'd check the plumb-ness of the wall and I'd monitor it's movement (plumb-mess). Hybrid walls (concrete and masonry) are tricky and need special consideration. Reinforcing needs to be embedded the correct depth and set the correct distance from the "load" side of the wall. Back when that was built, they built it "the way they've always done it." Seldom did they rely on calculations. – Lee Sam Jun 4 '17 at 21:10
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From the looks of it, you live in an old house. From the pictures and your description, you have a stone foundation with brick walls. Where the wall narrows is where the brick sits on the stone. The walls in the basement(stone and brick) were parged. It looks like you have a superficial crack in the parge coat. I would scrap all the loose material off, and repaint with a thick paint intended for basement walls.

  • Thanks. I pulled off a loose piece and updated the question with a detailed photo of it. Seems there's a white then gray then white layer and then loose rocky substance - underneath the loose piece, all I could see was that loose rocky substance. I wasn't sure if I should keep going or if this was actually structural. – Mike Eng Jun 1 '17 at 2:35
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    The brown is almost certainly parge coat. The grey may be a piece of mortar. You can keep digging and widen the exposed area; in the worst case, you will need to repoint the stone. But it doesn't look bad to me. Instead of just painting over it, you could just take a few more loose pieces out, and patch with mortar (with a little extra sand to make it softer) and then paint. – Edwin Jun 2 '17 at 2:52
  • Thanks again. I kept digging and updated the question with what I found. Turns out the foundation wall is concrete with masonry blocks stacked on top of it. I'm guessing what I revealed in the concrete foundation wall needs some professional help. What is your assessment? – Mike Eng Jun 4 '17 at 18:51

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