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Old 04-08-2011, 04:04 PM   #1
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damp concrete floor in shop


Hey guys, hope I put this question in the right forum.

Had a house built last year with a shop attached off the back of the garage, typical poured concrete floor, foundation, etc.

I have noticed that areas of the floor of the shop are on the damp side, enough that you can run your finger over it and have it come up wet. Now this is a time of year when humidity is very low and the shop floor is about 4 feet above grade. Even in the summer when humidity was at its highest I did not notice this.

I had a shop built on to my previous home in the same way, and there was never a single bit of moisture on that floor.

Is this natural or something to be concerned about? Thanks

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Old 04-08-2011, 07:00 PM   #2
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Hey guys, hope I put this question in the right forum.

Had a house built last year with a shop attached off the back of the garage, typical poured concrete floor, foundation, etc.

I have noticed that areas of the floor of the shop are on the damp side, enough that you can run your finger over it and have it come up wet. Now this is a time of year when humidity is very low and the shop floor is about 4 feet above grade. Even in the summer when humidity was at its highest I did not notice this.

I had a shop built on to my previous home in the same way, and there was never a single bit of moisture on that floor.
Is this natural or something to be concerned about? Thanks
Where do you live?
How was the garage slab setup?
How much precipitation did you receive this Winter?
You need to provide a few details. This isn't the Psychic Forum.
Ron

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Old 04-08-2011, 07:35 PM   #3
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I live in frigid Wisconsin. The foundation was poured, and then the flatwork was poured over gravel fill.

We had a lot of snow this winter and it was in the process of melting when I noticed this, however the slab was well above the level of any of the snow.

Just thought it was strange because this never happened in my previous shop, where the floor was much closer to ground level.
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Old 04-08-2011, 11:21 PM   #4
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damp concrete floor in shop


Is the shop on a hill? I don't understand:
"the slab was well above the level of any of the snow." We had 65+ " of snow this year. How could the snow not be above the slab?
Was there any vapor barrier under the concrete? Insulation?
How's the drainage? If the snow melted or it rained a lot, the water could be held in the gravel under the slab, wicking up.
How about short leaders close to the building? Clogged gutters overflowing?
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Old 04-09-2011, 07:46 AM   #5
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Do you have a vapor barrier under the slab?

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Old 04-09-2011, 09:16 AM   #6
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The lot slopes downward as you go back. At the front of the shop the slab is close to grade but at the back it's about 2-3 feet above. I originally overestimated because I was thinking of before they did the rough grade.

Although we had a lot of snow, I don't think it ever mounded high enough in the back to get to the height of the slab. It would snow a lot, melt a little, snow again, etc. As you can see the ground slopes away from the building and the red line indicates about where the slab is.



I'm guessing there was not a vapor barrier. I wasn't there the day they poured and there wasn't anything down the day before. I do recall seeing vapor barrier in the basement the day before they poured.

Perhaps they put a vapor barrier down when they built my old shop and that's why that floor never showed wetness.
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Old 04-09-2011, 02:05 PM   #7
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Richo,

Vapor barriers aren't required here in WI by code unless the garage is to be heated. We almost always put them down anyways, as it really costs pennies on the dollar, and they make a huge difference in floor sweating. There is no easy cure later for this problem. Are you by chance using unvented heat in the shop? Doing so can create large amounts of humidity that could easily condensate on a cold, non insulated surface like the floor.
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Old 04-09-2011, 04:50 PM   #8
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No, the heater I use is vented. The floor is still like that even though I haven't used the heater in weeks. The builder knew I was putting in a heater but it looks like they didn't bother putting down a vapor barrier.

Sounds like moisture is just seeping through the concrete.
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Old 04-09-2011, 08:41 PM   #9
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No, the heater I use is vented. The floor is still like that even though I haven't used the heater in weeks. The builder knew I was putting in a heater but it looks like they didn't bother putting down a vapor barrier.

Sounds like moisture is just seeping through the concrete.
It looks like you'll need a dehumidifier.
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Old 04-09-2011, 09:05 PM   #10
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No, the heater I use is vented. The floor is still like that even though I haven't used the heater in weeks. The builder knew I was putting in a heater but it looks like they didn't bother putting down a vapor barrier.

Sounds like moisture is just seeping through the concrete.
I should note that the code for vapor barrier & floor insulation has only been in place since April of 2009. IF a heater is to be installed in a garage since then without the required insulation, there needs to be a thermostat that limits out at 50 degrees installed. Thank God big brother is watching out for us I can't imagine how many of those t-stats get thrown in the garbage after occupancy inspection................
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Old 04-10-2011, 02:12 PM   #11
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Dehumidifier is right. Just had our first warm day of spring and humidity is high. My cast iron table tops on my machines are rusting and the floor is soaked.

I wish I had known all of this ahead of time where I would have made sure they put a vapor barrier down.

Thanks for the info.
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Old 04-10-2011, 02:34 PM   #12
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Is there an outdoor water spigot on the side of the house? (Right side of structure in the picture)
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Old 04-10-2011, 03:45 PM   #13
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No, but there is one that comes out of the back of the house immediately to the left of the shop
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Old 04-10-2011, 06:17 PM   #14
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No, but there is one that comes out of the back of the house...
Good, I was thinking broken water line in the slab.
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Old 04-11-2011, 02:49 PM   #15
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damp concrete floor in shop


I work at Gordon Energy & Drainage in Kansas City. I have diagnosed thousands of wet basements here. What I see in your picture is condensation. Condensation is always the hardest one for me to explain to homeowners. They always want to point their finger at a drainage issue or water table under the floor slab. But, fortunately, your problem is not as serious as that. Lucky for you! First, if the problem was due to hydrostatic pressure from under your slab, you would see water coming up where the floor meets the wall, or floor cracks. I bet if you drilled a hole through your slab, the gravel beneath the floor is dry! You need to remove the moisture that is in your concrete slab with a dehumidifier. THIS MAY TAKE SOME TIME!!! Once all the moisture has been removed from your floor slab, the discoloration should diminish. This is a common problem on newer homes and I have seen it many, many times.

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