# Moisture forming under rugs over concrete floor



## ZTMAN (Feb 19, 2015)

The moisture is most likely coming up from under the slab. If you want to see, put a piece of plastic on the floor. Tape it around all four sides to seal the plastic to the floor. Check it the next day for moisture between the floor and the plastic. Something like this

https://www.youtube.com/watch?v=Dm_ZUaqybug


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## SeniorSitizen (Sep 10, 2012)

The moisture test has already been accomplished with the rubber backed rugs and it tells absolutely nothing other than the air underneath has reached dew point temperature just the same as if the windows were sweating with condensation.

Solution: raise the concrete temperature or lower the moisture content of the air.

Run the numbers on this link and you can see at what concrete surface temperature and relative humidity the problem will be solved.

http://dpcalc.org/


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## 6string (Mar 3, 2015)

SeniorSitizen,

I'm thinking it has more to do with the indoor humidty. I've pushed it well past what I should in the name of comfort. I was getting water condensation on the windows, and knew I was pushing it. I lowered it, and contemplating turning it off.

I think its the humidity because we have NEVER had a problem, neither did the previous owner. The previous owner used to have those self adhesive linoleum tiles down there, for years, and never had a problem. With the amount of moisture I saw, there is no way those tiles would have stuck. 

The only changed variable is me cranking up the indoor humidity.


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## SeniorSitizen (Sep 10, 2012)

QUOTE: So, I'm guessing the moisture is coming from the air inside the home and due to the science of relative humidity (do I sound like an idiot? Good, because I don't know what I am talking about) the moisture is getting trapped underneath the rug.
*************************************************************
No you aren't an idiot but have a good perception of the problem.

Being there is a walk out I would not be surprised if the floor surface temperature was different by several degrees between the walk out side and the opposite side of the basement. If you can measure the floor temperature where the rugs are and room temperature we can get a general idea what the humidity level is and have some numbers to work with rather than just guesstimates. You may not have too much to be concerned about.

I've worked in shops where there was a throw rug at the walk in door entry. Some mornings the water would be under the rug and other mornings not. Weather conditions along with concrete temperature change next to the outside wall and door mostly ruled that scenario. The tools were never plagued with rust.


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## joecaption (Nov 30, 2011)

Often times the screw is metric, use a standard wrench and it's going to just round out.


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## Nestor_Kelebay (Jun 17, 2008)

6String:

No, it's not the indoor humidity in your house that's causing moisture to accumulate under those rugs. The rubber backing on those rugs is acting like a vapour barrier, effectively isolating the concrete under the rug from the air above. If that wasn't happening, the concrete under those rugs would be dry just like the rest of the floor.

What you're seeing is moisture migrating up through your concrete and accumulating under those rubber backed rugs. You can confirm that by buying a cheap hygrometer (measures relative humidity) at any local school supply place or online, setting it on your concrete, covering it with clear plastic and taping down the perimeter of the plastic to isolate the air under the plastic. If you see the hygrometer needle rise gradually to 100 percent before condensation starts to form on the underside of the plastic, that's proof that the moisture is coming up through the concrete.

What I'd recommend is that you buy a 100% Olefin carpet roll end at any retail flooring store and use double sided carpet tape to tape the perimeter of the carpet down to your concrete floor. Without an underpad under the carpet, any moisture that accumulates under the Olefin carpet will simply evaporate through the carpet. Here in North America, all the wall to wall carpeting (aka: "broadloom") made is made of either nylon, polyester, olefin or wool. Olefin is the fiber most resistant to moisture, which is why I'm suggesting that you buy Olefin.

Every retail carpet store will likely have a roll end they're selling cheap that you could use in your laundry room. Most often carpet comes in 12 foot widths, but the rolls they have might only be 4 feet long, in which case they'd meet your needs. You could also do the same thing with Polyester or Nylon carpet as well if you'd prefer.


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## SeniorSitizen (Sep 10, 2012)

The next time you get the urge to do the plastic tape down test where you are certain moisture is wicking up through the concrete try this. Tape a 18"x18" piece of aluminum foil to the concrete keeping it as flat to the floor as possible with contact to the concrete preferred. No wrinkles. Reynolds makes some good heavy duty foil that should work well.

After the foil has been taped down and sealed to your satisfaction, do the 12x12 plastic taped on top of the aluminum.


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## Nestor_Kelebay (Jun 17, 2008)

And so what would that prove?

You'd suspect that condensation might be collecting under the aluminum foil, but no way to prove it without pulling that foil up.

And, you'd have no condensation forming under the clear plastic since both the foil and plastic would be effective vapour barriers.

Why would be the point of doing such a test?


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## MTN REMODEL LLC (Sep 11, 2010)

SeniorSitizen said:


> The next time you get the urge to do the plastic tape down test where you are certain moisture is wicking up through the concrete try this. Tape a 18"x18" piece of aluminum foil to the concrete keeping it as flat to the floor as possible with contact to the concrete preferred. No wrinkles. Reynolds makes some good heavy duty foil that should work well.
> 
> After the foil has been taped down and sealed to your satisfaction, do the 12x12 plastic taped on top of the aluminum.


So what is the theory and what are the conclusions.......

I'm thinking like Nestor


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## concrete_joe (Oct 6, 2014)

6string said:


> Plus, I live in MN and the ground is completely frozen, so I doubt its leeching up from underneath.


completely frozen outside, not under your slab. the dirt under your slab has plenty of moisture that can migrate.

increasing inside humidity will cause water to migrate into equilibrium. it is possible that the increased humidity is wicking into the slab and then being trapped under the rugs.

you are not in arid land, thus i suspect your locale codes require a vapor barrier under all slabs. do you know for sure if there is or is not a vapor barrier under your slab?


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## MTN REMODEL LLC (Sep 11, 2010)

Senior... if like you say... the concrete is too cold and the humidity is too great... water condenses under the rug just like on a window.... so why does it not collect on all the concrete....

because it can still evaporate in the air... not because the concrete is colder under the rug.

It is a pretty common concrete moisture test to tape on some plastic... not a test of concete temp verse relative room humidity....

I think you have greater humidity coming from the slab, that is unable to evaporate in the ambiant room temp.

I don't think the solution is too raise the concrete temp or lower the room humidity... I think it is too let the moisture from the concrete evaporate by not using a rug that is a vapor barrier.

i'm willing to learn though.

Best


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## Gary in WA (Mar 11, 2009)

From BSC; carpet or box acts as insulator; cooling slab under carpet. All slab is at same dew-point- including under carpet. This lower temp causes high humidity level under carpet area. *Page 48;* http://www.buildingscience.com/docu...ybrid-foundations-retrofits-measure-guideline

Gary


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## concrete_joe (Oct 6, 2014)

post #12, not really a solution. excessive moisture migrating out of soil into home can be a hazard in many areas of the home as well as a health hazard, thats why i was asking about vapor barrier. 1st step would be to determine if a vapor barrier is there or not as this can rule out ground moisture, or possible lead to a broken vapor barrier and possibly a leaking pipe.


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## txpackers (Sep 11, 2016)

I have a similar issue I hope someone can help me with. I live in GA. I have a fully finished walkout basement. The entire basement floor is tiled with either porcelain or ceramic tile that looks like wood. I have a whole house dehumidifier that manages the humidity in the basement. I have it set to keep the basement at 45%.

Just recently I noticed moisture beneath two throw rugs on the basement side near the walkout. They're about 15' from the walkout doors. One rug was a rubber workout mat. The other looks like a Persian rug. I'm not sure what kind of backing it has. The Persian rug was completely soaked. What is strange is within 5' of these rugs are a different style of workout mats and no moisture beneath it. Also on the other side of the basement (about 25' away) is another rug that I know is nylon pile. No moisture at all beneath it.

Any idea what may have caused this? Both the rugs are near a bathroom which has me thinking I may have a pipe that broke in the concrete and is slowly leaking. I'd think I'd have a much bigger problem if that was the case. I removed both rugs and the tile has remained completely dry.

The entire basement is fully open and finished. The steps come down near the center of the basement. The dehumidifier is in a mechanical room on the left side of the steps and the inlet and outlet for the dehumidifier is on that side. The problem with the moisture under the rugs is on the right side of the steps.

Any ideas or suggestions?

Thanks.


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## SeniorSitizen (Sep 10, 2012)

By taking the floor surface temperature, I believe you'll find the floor has reached dew point temperature in the areas where condensation is beneath the rugs and the rubber backed excel in this department..


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