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My basement walls are wet above grade on the outside of my house, does anyone know what's causing this? This is after a night of rain and after everything getting mostly dry.

Inside unfinished and mostly dry but I do have an active french drain system.

I'd like to finish my basement but working to fix all the water problems first.

this is where it's wet on the outside

another side of the house where it's wet but happens on all sides

here is what the inside looks like

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    The question doesn't really make sense. The masonry surface, because of its porosity will hold the water from the previous rain for longer than most other surfaces. I think you may be finding problems where there aren't any. – Paul Logan Nov 19 '17 at 17:10
  • If you don't have any serious water or moisture problems on the inside, you should be in the clear. You could always treat the outer surface of the foundation wall with a sealing material then apply another coat of good quality exterior paint. – Paul Logan Nov 19 '17 at 17:14
  • Thanks for the recommendation about the sealer, I was thinking of doing that but was worried it would prevented needed ventilation to dry out. Once I seal off interior walls with xps foam board the only method for vapor to come out of the wall will be through exterior above grade section. Thoughts on that? – Vk10000 Nov 19 '17 at 17:34
  • If you had to leave one side unsealed, which would you prefer? Also what"s motivating you to put the insulation on the interior not the exterior? – Harper - Reinstate Monica Nov 19 '17 at 17:54
  • i was thinking interior should have a moisture barior to avoid wall drying toward inside to avoid mold and water getting in contact with the finished wall. Please reccommend how you would finish a basement. The water table is high around my house, also it is kind of at the bottom of a hill right where the slope ends. I spent a lot of time readIng how to finish it and that's what I found. But I'm not an expert. – Vk10000 Nov 19 '17 at 18:19
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There could be two issues: 1) moisture dripping off the building paper under the siding, or 2) moisture entering the masonry cells.

1) We install building paper (moisture barrier) under exterior siding because we know the siding will leak. Well, that moisture needs to run out at the bottom of the wall. If the siding is leaking really badly above this area for some reason, all that moisture could run out long after a storm and “wet” the wall.

2) If you look closely at the interior block wall, you’ll notice some discoloring (darker areas) aligned vertically. This indicates moisture is getting into the cells and filling with water. (Masonry blocks are hollow and often not filled with grout when the wall is constructed.) This allows moisture in the ground to seep into the concrete block cells. (Yes, masonry block is porous.)

Also, if the window in the first picture is the same window in the interior picture, then these moisture spots align perfectly. This could mean the cell is “full” of water.

Heat will “draw” moisture out of a wall. (That’s why paint on south facing walls blister more than other walls.) So, where the cells have moisture, the sun could draw the moisture out and cause the discoloration.

I’d: 1) check to see if moisture is running out from behind the siding by rolling a few paper towels up and stuffing them up under the bottom of your siding at the wet area AND at the dry areas. Then compare after a storm, 2) Dig down a few feet at the wet spot and see if the moisture barrier on the outside of the basement wall is damaged. I’d also make sure the material (soil) is porous so the moisture can “flow” away from your wall. If it’s not, I’d replace with drain rock. (Round river rock without fines...no rocks smaller than 1/2” dia.) Worse case: you’ll need to install a French drain to carry the moisture away from the wall.

Regardless of where the moisture is coming from, I would NOT finish the interior until you find and stop the moisture because it will cause mold.

...but I don’t understand what is happening at the top of your wall inside. Is that insulation?

| improve this answer | |
  • You are correct the inside is the corresponding picture of the wall next to the window where it was wet on the outside. I drilled weep holes at the bottom of the blocks a couple months ago so if the blocks had any water in them it would drain out into the french drain but this section is very dry and never seen water flow into the french drain. I'll try your paper towel idea and was worried about the same thing but dismissed it was not possible. – Vk10000 Nov 19 '17 at 18:45
  • Top of the wall came like that when I bought the house it probably insulates the sill plate from moisture coming out of hr blocks – Vk10000 Nov 19 '17 at 19:25

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