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Above grade cinder block basement wall is wet. It's right at the ground level. On same wall the below grade isn't wet. i think it's b/c not much sun on that side of the house as other. what to do? Hoping to finish the basement. Put XPS board on wall and still wet, but only in a couple of spots. very strange.

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  • This sounds like a drainage problem. What's the grading on that wall like? – iLikeDirt Feb 3 '15 at 20:37
  • Don't think it's drainage issue. The below grade block is dry. only the above grade 2-3 blocks is getting soaking wet. Only started when i began to finish basement and put XPS board on. Today i took the XPS board off the wall before work and now it's dry. It only gets wet when XPS board is on. Almost like i need to insulate in between block. How the heck do you do that. thanks! – Lisa D Feb 3 '15 at 20:57
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I have had this problem. The block on my basement wall was not sealed. When it would rain for a very long time it would eventually saturate the block and start to soak through. The blocks would fill up with water and it would take weeks to dry. Use seal or paint to seal the block that is exposed to the weather and it should help.

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  • Don't think it's drainage issue. The below grade block is dry. only the above grade 2-3 blocks is getting soaking wet. Only started when i began to finish basement and put XPS board on. Today i took the XPS board off the wall before work and now it's dry. It only gets wet when XPS board is on. Almost like i need to insulate in between block. How the heck do you do that. the wall is facing North. – Lisa D Feb 3 '15 at 21:24
  • @LisaD - Probably, if you tore the wall apart, you'd find that the hollow block cells have been cement filled up to the 2-3 block tier. As Lee points out, water soaks into Cinder Block. It will pool on top of the cement plugs and capillary out through the block material in a band around the basement at that level. The only other time I've seen that is when somebody put a copper water pipe in the wall and it developed a pinhole. It develops a damp band on the sealed tier of Cinder Blocks. And if the winter winds tend to come from the north also, it's likely the north wall gets a good soak. – Fiasco Labs Apr 5 '15 at 0:52
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If the blocks get wet when your insulation boards are up, and they dry again when you remove them, that points to the boards being the determining factor. Those boards insulate the blocks, so they're kept colder than they would be if they were uninsulated from your house's heating system. Colder walls can (and in this case apparently do) get below the dew point, which means that any humid interior air that touches the wall will condense into liquid water. This is probably not happening to the below-ground blocks because the warmer temperatures there are keeping them from getting below the dew point. But the blocks exposed to outside air can get very cold indeed!

You did the right thing by putting up rigid XPS foam. However, apparently you haven't sealed the boards well enough to protect the block walls from interior air. Now that you've cut the walls off from heat, you need to cut them off from air as well. I would suggest caulking the seams of the XPS boards and taping over that with high-quality tape, spray foaming them to the ground and the rim joist, etc. Basically, you want to make sure that the air in the basement can't touch the block walls anymore. That should solve any moisture problems originating from interior air condensation.

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  • i did do what you suggested except didn't seal/foam all around the top. I'm going to try out a section and see what happens. thanks very much!! – Lisa D Feb 4 '15 at 2:09

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