masonry block foundation moisture problem


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Old 07-26-06, 11:36 AM
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masonry block foundation moisture problem

Background:
Living in 8 year old home with block foundation. Basement unfinished but had been framed in on exterior walls with 2x4 and fiberglass insulation. Also has poly over the insulation as vapor barrier. Since house is a walkout, the sides of foundation "stepdown" . So in effect, the basement has shelves where block resides. We have had temps in the 90s lately with high humidity. So air conditioning always running..

Problem.
Looking at the poly I saw what looks like mold (above the block shelf). upon further investigation, it looks like moisture condensating on poly.
I pulled back the poly and the fiberglass was quite moist. I noticed that it was only wet on inside not on the side facing the outside sheathing. I also noticed that it appeared to be most wet on the block ledge. The block ledge has cracks bewtween the blocks that are open.

Question:
I haven't ruled out moisture leaking in through the walls somewhere, but we also have been in somewhat of a drought and have not had rain recently, but maybe humid air infiltration.
But,
Is it possible that as the day heats up that moisture in the hollow blocks heats up and convects upward where it ends up condensating on the poly since it is much cooler in the basement with the air conditioning runninng all the time?

Can I seal those openings between the block with something like spray insulation? or something else?
 
  #2  
Old 07-27-06, 03:52 AM
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To attack this moisture problem, one must first determine the source. Let's talk about the inside of the basement first. You live in a hot steamy (humid) climate, right. So you must operate with adequate dehumidifying equipment.......no exceptions. Air conditioners help but they do not qualify as dehumidfiers. You have decribed having a layer of visquine over (inside) basement wall studding which has been insulated. That should miinimize some moisture condensation on surface of cool blocks.

For now, this means we might have to turn our guns on the outside you have described as a walk out which means you are built into a hillside. What type of waterproofing materiel was used? Block masonry foundations can shrink as they season causing hairline cracks. They (especially walk out basements) can suffer stress cracks as backfill settles against walls and other forces apply pressure. Checks or cracks in walls may lead to infiltraion of moisture which migrates inside and becomes trapped against a moisture barrier on he inside.

1: Has the walls been backfilled with a granular type fill?

2. Are there eaves on house and do they discharge well away from foundation? Does grade slope away?

3; is the outside of the basement block waterproofed and with what?

4; Has the footing been tiled below floor level and how does this tile drain? to where/

bs5
 
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Old 07-27-06, 07:32 AM
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thanks for replying
More information; the moisture I see condensating is on the level above the blocks. Of course that doesn't mean the moisture isn't coming in at the block level. It is humid this time of year, but not always.
I live in minnesota, which means it also gets cold during the winter. For that purpose we do have an HRV or air exchanger. I normally shut that off during the humid periods so as not to bring in the humidity. I also have a portable de-humidifier in the basement. It helps but probably not to effect ytou are referring.
to answer your questions

answer to questions
1. I am not sure on what the backfill is. As far as I know it was just the backfilled with the excavated soil which is mostly sand. though there does appear to be some clay in spots.

2. as it wopuld have it, the areas that show the moisture are on the rake side of the roof line meaning no discharge from roof. The grade does slope away from house, though I do see signs of settling right next to the foundation ins certain areas. Probabluy was not backfilled properly.

3. The foundation was waterproofed on outside with some gray spray on material. I am not familiar with what it is. I know it was somewhat new for our area anyway about 8 years ago. So I could see how cracks in the foundation may let moisture in. I don't see any cracks above grade anyway.

4. yes foundation does include drain tile which drains to a sump which pumps outside. However, I rarely see that filled with much water.

weird thing I noticed abput the blocks. It has poly next to the blocks, then the insulation and then again poly outside of the insulation (inside wall). I thought that the vapor barrior should only be used once.

thanks again
 
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Old 07-27-06, 07:33 PM
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Sand is OK for backfilling a basement excavation and clay is no good.

Still sounds like moisture is entering block cores and becoming trapped by the visquine on either side of block masonry walls.

BTW, a visquine vapor barrier for inside a basement wall belongs on the living side (inside) framework over insulation......i.e. beneath paneling or drywall. The vapor barrier does not belong between framing and blocks. Water vapor from warm inside climate can continue right through unprotected drywall, unfaced insulation and framing and condensate on cold outside walls. A visquine vapor barrier covering the walll at the block wall behind framing and wallsurface is absolutely worthless and possibly even counterproductive.

bs5
 
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Old 07-27-06, 09:00 PM
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ok thanks.
It maybe hard to remove the plastic against the foundation wall now, so I may just cut it (as you would kraft faced insulation) thus using only the vapor barrier on the living side of the wall.

I am also planning on sealing up those holes/cracks on top of the wall with the canned expandable spray insulation. I did observe warm moist air coming from there when the sun was shining on that side of the house.

So there must be moisture in the core of the blocks as you suggest. I will need to determine if how it is getting there. Like I said earlier, I had noticed some settling along parts of the foundation, so I may start digging there to see whats up.

thanks again
 
 

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