Floor Sweating

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Floor Sweating

Postby thailazer » Wed Apr 11, 2012 8:55 am

We have one room in the house that does not get much air circulation and I am noticing water droplets under anything plastic placed on the floor. The concrete is 1 month old and has a coat of A100 acrylic sealer on it. Is the water that I am seeing coming from humidity in the air or is it coming from the concrete itself? I always thought that concrete would absorb water as it continues to cure over time, not give it off, so am curious what the experts say here. I never say anything like this occur on floors poured in the USA by the way.
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Re: Floor Sweating

Postby Roger Ramjet » Wed Apr 11, 2012 12:17 pm

thailazer,
Humidity in the air and plastic placed near the floor is causing the water droplets.
Even in the deserts of Australia you can get water to form on plastic at night as there is a difference between the ground heat and the night air.
I can post the scientific explanation if you like but this diagram may help: http://www.wikihow.com/Make-Water-in-the-Desert
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Re: Floor Sweating

Postby thailazer » Wed Apr 11, 2012 12:54 pm

Roger I get that as I used to teach survival training so very familiar with that concept. In my situation, there is not much air in the area between the plastic and the concrete, so not much humid air mass to condense. I suppose it is possible that air is getting in there and condensing though. Going to have to watch this a bit as it doesn't make sense to me yet. Don't want any source of moisture in our walk in closet.
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Re: Floor Sweating

Postby thailazer » Wed Apr 11, 2012 2:36 pm

Some more data: My wife just picked up a thick paperback book she is reading in the bedroom and the back cover is quite wet. It was laying on the concrete for about 18 hours. Seems to me the moisture is indeed coming up through the floor as this room has excellent ventilation. Is this normal?
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Re: Floor Sweating

Postby fredlk » Wed Apr 11, 2012 2:48 pm

thailazer wrote:Seems to me the moisture is indeed coming up through the floor as this room has excellent ventilation. Is this normal?

I have a concrete house and an untreated concrete floor in a well-ventilated basement and the floor there (and elsewhere) is always bone-dry. In fact I store a roll of cardboard in there and it's still in good shape. The basement floor was poured directly on top of the soil.
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Re: Floor Sweating

Postby thailazer » Wed Apr 11, 2012 2:58 pm

Fred... That is my past experience too. How old is your floor? I am thinking that our Acrylic Sealer trapped in the moisture, which you want for a good slow cure, and that it is still releasing moisture after a month. I would have thought that hydration would have taken care of the majority of the moisture within the first seven days, but not sure of that. The sweating is quite a noticeable effect here on our young concrete.
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Re: Floor Sweating

Postby fredlk » Wed Apr 11, 2012 3:09 pm

thailazer wrote:How old is your floor?

The basement floor has been there for at least 12 months and as far as I can remember has never shown any signs of dampness even though the soil wall behind it is often a little damp through seepage.
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Re: Floor Sweating

Postby geordie » Wed Apr 11, 2012 4:03 pm

I am guessing :roll: the acrylic sealer has trapped the moisture in the concrete i dont supose it was microporous ?? BUT its recomended in uk no ""vinyl"" floor covering for a minimum of 8 weeks to allow the concrete to dry out so without the a100 you would have to leave it 2 months :( with it is debatable but definately a long time always leave a small airgap under anything you leave on the floor and in a couple of months test it with a plastic object again you can remove the sealer with certain chemichals one of which is contained in (UK ) truckwash i would be inclined to just use caution for now long term it should resolve itself
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Re: Floor Sweating

Postby thailazer » Wed Apr 11, 2012 6:08 pm

Thanks for the Geordie. I never heard of the 8 week rule on waiting to cover the floor but it makes sense. Trapping the moisture in with A100 is a good thing as the concrete will be stronger, and it does appear to be more of a problem where he sealer is a bit thinner. No plans on removing the sealer as I am fairly sure this will resolve itself in time. With all the concrete experts cruising CTH, I am surprised to not see any responses from the real experts. The amount of moisture that appears seems less this week than last week.

Concrete is complicated stuff. We left a large porcelain sink laying on a the concrete for a day when the concrete was only a few days old and in 24 hours it pulled a white stain to the surface. The stain is still there.
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Re: Floor Sweating

Postby geordie » Wed Apr 11, 2012 8:06 pm

The chemical process in concrete sets it ?? the water is just a nuciance once its laid there is leaching tp the syrface as it dries which is why you can sweep and mop daily for weeks and still get a fine residue from it ??hence the sealer But i was once told as a lad the cure time is 100 years then it starts to go the other way deteriating although we still have example,s of "roman" concrete credited with being the first to use it you could move the sink around till it matches ??
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Re: Floor Sweating

Postby thailazer » Mon May 14, 2012 1:42 pm

Here is an interesting link I thought I would post in case anyone has this problem as well. Looks like porosity of the concrete plays a big role. Our floors are very dense with the surface additives used, and the A100 on top of course plays a role in sealing them further. It is still a mystery in one area as adjacent tile does not sweat at all, and the floor in a room with the least air movement does not sweat either.

http://www.concreteconstruction.net/interiors/sweating-slab-syndrome.aspx
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Re: Floor Sweating

Postby las vegas paving » Thu Jun 28, 2012 8:23 am

You did not say what type of home you have but walls and floors sweating is really condensation which is a result of the relative humidly in your home and the temperature of the wall or floors surface. Like a cold glass of water on a hot day. You have two choices ether lower the humidly ( with a dehumidifier or by ventilation) or raise the temperature of the wall and floor surface ( insulation is the best way depending on the construction of your home)Raising the temperature in your home may or may not help sense the warmer the air is the less moisture it will hold although you could try it to see if it might make a difference.
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Re: Floor Sweating

Postby Maseratimartin » Thu Jun 28, 2012 9:29 am

Regarding plastic on concrete floors Roger is really and expert... ;)

A one month old concrete has still a high level of water but this should now be blocked by your sealer.
On the other hand the sealer does not allow now anymore the concrete to absorb humidity.
If you now also seal of all walls with paint then the humidity has no where to go if not sufficient ventilation is provided.

Look that you create some air flow or the next step will be that mold grows...

Such things are typically for totally sealed basements/ cellars.
There is a reason why old wine cellars are not sealed....
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Re: Floor Sweating

Postby Roger Ramjet » Thu Jun 28, 2012 9:58 am

For those of you that live in townhouses there is a simple experiment that you can conduct yourselves, if the townhouse has a toilet and shower under the stairs with no ventilation. Just close the door overnight after you have had a shower, then in the morning you'll find it is not only humid in the shower/toilet, but also a lot hotter than the temperature outside the shower/toilet. You don't really need to have a shower as the enclosed concrete space with no ventilation will do the trick, especially if the shower/toilet is in the middle of the townhouse.
If anyone is interested I'll even conduct the experiment again as I have two wall clocks that show both humidity and temperature.....and I'm bored waiting for my drain and wall to be finished... and I love science and experiments... and my favourite particle physicist Brian Cox's new lectures on the universe are not being aired until July.
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