Moisture on Foundation Wall
I’m in CZ4 and installed 1.5″ foil-faced XPS to my basement walls over the last few months. We’ve gotten significant rain in the last week and I’ve been anxiously checking all this work to be sure water is kept at bay. All told there do not seem to be any issues save for one little 4′ area.
In this spot the XPS is off the ground maybe 1/4″ so I can see under it back to the wall. {For background there has been an interior drain system installed and there is a gap in the joint between the floor and the wall to allow any water that might enter above to flow down the wall and into the drain tile}. When I check this one spot there is just an ever so slight amount of moisture in the form of tiny beads maybe the size of a grain of sand or smaller. What I don’t know is if it is coming from below and the interior drain tile somehow or if it is the wall sweating and it’s running down the voids between my wall and XPS.
Is this minor amount of water a concern? Does it depend on the source of it? The amount of moisture is so small I can slide a paper towel under the XPS in this spot and it gets slightly damp but is not fully soaked, if that makes sense. I plan on eventually taping and sealing all these gaps and areas, but just wanted to see what the community thought about this potential issue before dropping tens of thousands of dollars into finishing the space. We’ve spent a lot of time and money just getting this previously defunct basement completely dry and braced, so am feeling a bit defeated with this latest discovery.
Thanks,
Michael
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Replies
Hi Michael,
No need to feel defeated, this is all part of the process. One trick I've learned over the years is to take a piece of duct tape and stick it to the area I'm most troubled about for moisture concerns. In the type of system your talking about for drainage of your foundation walls, water can still get trapped inside and cause moisture.
Take a small piece of duct tape and stick it to a few areas. Go where it is dry and also where it is wet. Observe the results over the next 48 hours. If the tape stays completely stuck to the wall your set. If not, there is water still being trapped inside the wall assembly. This can sometimes be solved with weeping holes to allow the trapped water into the interior drainage tile.
Thanks. Before I started installing the rigid, I taped plastic on the walls and floor in various spots to test for this. They all remained dry, even after some significant rains. That's why I'm a little perplexed by this. I don't know what would be more concerning - if the water is weeping up the wall from the floor and drain tile below or if the water is driving through the wall and running down behind my rigid foam. Of all the options I do not think it's condensation but is groundwater in some capacity, but I'm not a hydrologist or an engineer so that's just my instinct.
With the rigid already glued and secured to the wall, I can't put tape on the wall, but could try to slide some under the rigid at the floor where I have some gaps due to the floor not being level. Is that what you mean? Also, the only duct tape I have is Gorilla and that stuff is bulletproof - would you go with a cheaper brand for any type of moisture test?
Thanks
Yes I would try a grey role of duct tape. Less tacky the better. There may be a small amount of water still trapped in your foundation wall.
There is definitely moisture coming from somewhere - I don't know if it's trapped in the wall or capillary action from the interior drain tile or footer up the wall (house was built in 1956 so no PT and no capillary break b/n footing and wall). I slid a paper towel under the rigid foam and left it for about 48 hours. When I pulled it out today (after having no rain for several days), it was noticeably wet. Again, not soaked but was in contact with water. I did this in several spots and only one was wet - I guess that's the good news. That leaves me wondering a few things.
First - is the sign of any moisture, period, reason enough to not finish the space - even very small amounts that will eventually be sealed? Is there a moisture gradient where it takes more than a damp paper towel to cause heartburn?
Second - per my earlier comment, do trace amounts of moisture seem less problematic if the rigid is taped, sealed, and caulked.
Third - doing the plastic tape down test before embarking produced no signs of moisture on either side of the plastic on a number of spots on my walls and floors. Is the insulation causing the moisture to appear? Would the smart thing to do be to forego the foil-faced rigid, either by removing the foil or just not using any rigid at all?
I know the decision is ultimately mine to make, and I'm leaning towards sticking to the assembly I've started (concrete wall --> foil faced XPS --> rock wool --> sheetrock -- latex paint). But, if there are good enough reasons not to by someone better informed than me, I would certainly listen to any and all positions.
I think your assembly is fine. I personally would drill a few more weeping holes below grade to allow trapped water to escape. This happened to my older sibling who had a finished basement, interior drainage tile, but incorrectly placed weeping holes. After correctly drilling the weeping holes, the water was released from the wall and moisture issues were abated.
I would be reluctant to drill weep holes until I was sure where the water was coming from. If you have, for example, a crack or other defect in your exterior waterproofing, and that's where the water is coming from, drilling holes to the exterior could well make the problem worse.
I suspect your moisture is a very small amount that is migrating through the wall, and not bulk water. If you had bulk water issues -- what many would call a real "leak" -- you'd probably see streaks since the water would be flowing, a trickle coming in, or at least a steady stream of drops. Since you only seem to have a very small amount, that makes me think it's either moisture migrating through the block and condensing out on the exterior face of the XPS, or it's moisture condensing in that area that is getting there from inside.
Either way, you're probably OK with your current plans, just try to seal things up well. It's posible to build a sort of interior drain channel on top of the slab along the edge of the wall if you're concerned, but you need somewhere for that to drain to.
Bill
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Bill,
You're correct in that the amount of moisture is not bulk water but is less than a trace. Though, I would add the house was built in 56, so exterior waterproofing isn't in place (old clay drain tile surely clogged by now). For the amount of moisture, think of a bead of sweat, it's even less than that. For context, using a paper towel to dry my hands or wipe a sweaty brow would make it substantially wetter than the amount of moisture that is present on the wall. So, volume is not a terrible concern at this point and while I really don't want to see ANY signs of water, it's not a leak or pooling situation.
Also, just to be clear the EPS is foil faced (I incorrectly noted it as XPS first - it's not) and there is no moisture on it. I saw moisture where there is a gap beneath it in one spot where I can still see back to the wall. I'd also add the only reason I saw it is b/c it barely glistened off my flashlight - otherwise I'd never even have noticed.
I'm most baffled by where it's coming from and really just want to ensure it won't lead to mold problems down the road. I think if I do my best to seal it all up then hopefully that will mitigate 99% or more of my problem. Though I'm also learning to truly seal air in or out is more complicated than it sounds! Thanks for the feedback!