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Dyoung 02-12-2010 12:21 PM

WET concrete wall under TOP floor bathroom window---how to stop?
Hi Folks

I am gutting and totally redoing a bathroom in my upper floor home, built circa 1959.

I am ready to begin work on the bathtub area and building a frame for the hardiebacker sub-walls for tiling.

Since the heavy DC snow storms, the concrete block (cinderblock) wall under the bathtub window has stated showing signs of wetness. Note that the concrete wall has brick on the outside.

......even though I am going to rebuild the wooden hardiebacker support frame as the originally was quite rotted, I was also going to apply a liquid foundation sealer to the concrete walls around the window in an effort to keep ~outside~ moisture away from the hardiebacker. I was also going to use ""roofing felt"" in between the wall and the frame/hardiebacker. Sort of a one-two punch.

My question is this:

if I use a foundation sealer on my concrete wall, this doesnt necessarily stop the leaking INTO the wall in the first place....and the last thing I want to do is trap moisture in my walls. We have enough of a humid/wet basement to begin with.....undoubtedly due in part to leaky windows.

However, as far as sealing the bathroom goes, DOES IT HURT TO APPLY THE FOUNDATION SEALER TO MY BATHROOM CONCRETE WALL? Or should I just use the roofing felt?

I want to stop the moisture and sealing or felting up the window wont give me much peace of mind as I wont be able to tell if any future window sealing is doing any good.

Does all this make sense?

Here you can see the wet areas (darker areas). Ive placed a heater in the bathroom which is doing some good but its taking a long time. The heater has been there nearly 15 hours.

Rory Read 02-12-2010 12:35 PM

start with the window
You might want to take a very close look at that window. Odds are the water is coming in there, and you would do well to fix that before moving on to any interior work.

I would guess that you could then skip all the interior waterproofing, unless you are addressing water from the tub.



RDG Read Develpment LLC
Portland, OR

Dyoung 02-12-2010 12:39 PM

Hi Rory

Ive been told to at least use the roofing felt in between the hardiebacker and the concrete wall. I dont think that would be a solid seal such that it would trap moisture in the walls, just project the hardiebacker....and Im find with that.

Id LOVE to wait and fix that window but we have no bathroom at the moment and time is of the essence.

Rory Read 02-12-2010 01:14 PM

in that case...
  1. The HB backer board is pretty much designed to handle moisture. I don't think you need to worry about it getting wet.
  2. The wood framing for your backer board might rot if left exposed to enough moisture for a long enough time, so you could consider using PT instead of plain old green lumber.
  3. If you really want a vapor barrier, use plastic sheeting, and put it behind the wood. Felt paper is only going to act as vapor retarder. I am not sure I see the point in that. I don't like the barrier or retarder idea for the very reason you suggest. I am very cautious about trapping moisture in the wall. The cmu wall will do much better than a stick framed wall if left wet, but mold is still a concern.
  4. I understand that you need a bathroom. That's not a fun thing to live without. But, that moisture is going to continue to enter that wall, and it is going to go somewhere. If you are doing this work yourself, I will assume that, like me, your house is rather large personal investment. You can't let something like that fall too far down the to do list.
  5. You may not have to replace the entire window. If you can see where the water is coming in, copious amounts of exterior grade urethane caulk (OSI's Quad is more popular than Vulkem out here), might buy you enough time. You might at least get ahead of the drying curve.
  6. The water could also be coming in further up the cmu wall, but that doesn't seem likely.
What's above the bathroom?

Hang in there,


RDG Read Development LLC
Portland, OR

Dyoung 02-12-2010 01:50 PM

Yes I am using PT wood....thought about that a few weeks ago, as it made sense.

As for the barrier vs retarder, there seem to be various perspectives on this. What type of plastic would you recommend?? I have some of that unfolding roll plastic ....think that would work??

~IF~ the objective is to keep the hardiebacker AND the PT wood as dry as possible without necessarily sealing in the wall/moisture into that concrete wall....seems like felt paper would slow up the moisture enough such that its not absorbed into the PT wood or HB. As such this seems like a better idea than the

Yes I will have to get medieval with the caulk on my window when its warmer.

We have a basement level and above ground level... this bathroom in question is on above ground level. Only attic above us.

concretemasonry 02-12-2010 02:24 PM

If the wood is rotted, there must have been a long tern leak that never showed up inside.

There is a very good chance that the window was not installed properly and let in moisture. there could be a leak above the window and the water is stopped by the window and going around to the lowest point, which is common.


Dyoung 02-12-2010 04:06 PM

YES, I have discovered the problem with the leak.

The outside wooden widow sill portion is TOTALLY rotted away.

I pushed my finger right through it like soggy shredded wheat.

Ironically this is a weight of my shoulders in a least I know what the problem is. I stuck trashbags outside to keep melting snow from getting down in there.....and to no surprise, the wall is drying up. What a revelation!

Rory Read 02-13-2010 12:27 PM

short and long term fixes

That's great.

I suggest you go with a temporary fix over the the window, plastic, plywood, whatever it takes. Note that the rot on the sill may not in itself be proof that the water is not coming in above that sill, either on the window or closer to the roof. It is possible that flow is from above, through the sill, and then into the wall. Not likely though.

I suggest you do not add any interior vapor barriers or retarders inside the wall (I earlier failed to mention that a water barrier on the tile under layment is not uncommon and not a bad idea.) and that you complete your interior work as though you have a healthy exterior wall. No harm in the pt wood though.

I know you are in rush to a finished bathroom, but the longer you can let that wall dry out before covering it up the better. A few more days without it may be worth a lot more to you than a built-in mold farm.

When you get to that window, do your home work and go all out, full monty on the flashing, sill pan and attention to the drain plane.

Good luck. It sounds like you are on your way.


RDG Read Development LLC

Dyoung 02-13-2010 10:14 PM

Thanks Rory.

I think there may be some water leaking above, up near the roof or perhaps coming in vertically or near the top of the window with snow drifts, etc. Reason I think this is because there are parts of the concrete wall that are still semi-moist up high....higher than below the window itself. Ive got the heater on the wall 24/7. Its warm to the touch. Some moist areas may also be stained somewhat. Not entirely sure as they dont feel super moist per se.

"I earlier failed to mention that a water barrier on the tile under layment is not uncommon and not a bad idea."

--Yes I agree. I also now concur that sealing the concrete wall proper is unwise as it may trap moisture, potentially leading it downwards to the very foundation, definately not good. In fact this summer I plan on excavating the foundation to inspect it, clean it, seal it (the outside) and put in a french ditch.

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