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I recently poured concrete on an unfinished part of my basement floor. Shortly, after the job was finished, I encountered wetness on the floor when ever I sat an object down. I am baffled as to why this is happening. Has anyone come across this problem? Do you know of any chemicals on the market to help us? What would you suggest?
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Fred, thank you for your response. Will the plastic work even if the concrete has been down for four months. I poured the concrete in June and I still have this problem. Do you think that I should have put plastic down before I poured the concrete. Would you suggest I take up the floor and repour using plastic? I would prefer not to do this but if this is the only sure way, I will. Is it worth having the area checked by an engineer? How long does it take concrete to dry completely?
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Paula,
Not my area of expertise, but here's a little general info that may help you understnd the mechanics better...
There are so many misconceptions regarding concrete, unfortunately many of these misconceptions require labor and additional cash to correct.
Magnify a chunk of concrete a thousand times and it'll look like a sponge. In spite of its solid appearance, concrete is quite porous and as a result (as you now know) does not provide resistance to water vapor transmission. Water in liquid state will transmit through as well, if driven by sufficient pressure.
When you sink this pourous material several feet underground and subject it to hydrostatic pressure on one side (bottom of slab) and nothing to counter or balance that pressure on the other side (your basement space), mother nature and the laws of physics take over and you end up with a humid basement (vapor transmission) or, when the water table rises (Liquid transmission), a wet basement. It's an amazingly beautiful thing (as long as it's not your house) to see water percolate up through what appears to be a flawless slab of concrete.
A properly placed slab will be detailed to minimize the effects of water in both the liquid and gaseous phases on the slab. In your case, it appears that water vapor it passing through your slab and condensing on items you have placed on your basement floor. Where nothing is on the basement floor it is dry. Vapor is still passing through in these locations, there is just nothing for it to condense on, thus the appearance of a dry slab. This vapor then passes up into the living areas of your house where, if not properly handled, it can slowly rot your house. It's more a problem in new, tight construction. Older houses leak like sieves, so the water vapor that enters the living area via the basement is easily transported through those leaky walls and back to the outdoors. It's an invisible process until mold and rot start mysteriously appearing, usually in attic (cold, condensing surfaces) spaces. This moisture has been entering your house since day one. You're only noticing it now because the slab and boxes have given the ever-present vapor a chance to condense into a visible liquid.
The ideal solution would have been to properly detail the slab during its initial placement. Since that opportunity has passed, you first attempt should be to treat the slab as Fred mentioned. Clean it, then seal it. If the problem is minor, that should suffice. If the hydrostatic pressure overwhelms the sealer, more expensive solutions lay just over the horizon.
Is this a whole-basement slab or did you just pour in a portion of your basement? If just a portion was poured for a storage slab, you could do a surface sealer. Moisture will move to the area of least resistance, which will be the basement floor area that is still dirt.
Fred is certainly the man to listen to in this case, he's the resident expert on building envelopes. Take anything he says over my advice.
Strength-wise, concrete plateaus out about four weeks after placement. Moisture-wise, I honestly don't know, but I'd think 4 months would be more then sufficient.
A very, very primitive indicator of slab vapor transmission is to place a 24" square piece of poly om your slab. Tape the four sides down with duct tape. Check the poly a few days later. If water has condensed between the poly and slab, you have vapor transmission.
To experiment, use a sealer on a small piece of slab. Let it cure as directed. Repeat the poly/tape test over the sealed area of slab. If the poly remains dry, the sealer stands a good chance of being effective over the entire slab.
Best of luck.
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Mongo, you've been very helpful. I am really thinking about taking the floor out (14X12 area) and re-doing the job. You mentioned the ideal solution would have been to properly detail the slab first. Can you explain? The area was the part of the basement the builder closed off. I later removed the wall so that I could expand the living area in the basement. The builder would have done this for an additional cost but, I thought I could save money by doing it myself. The ground was covered with @2" of gravel.
I don't mean to keep going back and forth but, I'm trying to understand something that is way beyond me and get the best possible solution.
Thank you for your patience.
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Paula,
Do not remove this floor yet! There is a product/procedure to eliminate this water migration and actually increase the strenth of the concrete. I spent
three hours today talking to a rep. Check Protecete.com
Look at the product Densifier. Any flooring installers
might also be interested in improved adhesive bonding.
Food for thought, Rick
*protecRete? Thanks for the site.
*Paula, First try the sealer. If it works you've saved a large amount of labor and the expense of detailing and pouring another slab. Now, should you choose to break out the jackhammer...First ensure you have a decent base, leveled and compacted. Drainage tubes installed if required. They can be tied in to your existing under slab/footing drainage system. If your house has no under slab drainage and you haven't had any liquid water in your basement, you may not need to install them. From there, the typical layers are 4" of gravel, then a poly barrier, then 2" of sand, then your slab. The problem is that with all the walking done in placing the sand and concrete, sometimes the gravel chews up the poly. So, some will go gravel, then sand, then poly, with the slap on top. The downside to this is that the poly traps the water in the concrete. If the mix was too sloppy it can result in too long of a cure time, a weaker slab, and even slab curling as it cures.Catch 22, eh? I do know one guy that goes the first route and lay down a double poly layer. Added insurance, I guess. With your small pour you should be able to go the first route since there shouldn't be too much walking around.Good luck, hopefully the sealer will work well for you.
*PaulaYou'll get a ton of good information from this post, I'm sure.(sometimes it'll confuse the heck out of you). You might also looks at the archives in "heat and ventilation" as well as "construction techniques". Lot's of good info on this subject.
*Ditto. I had no idea concrete was so complicated until I tuned in here. I thought you just poured in in a hole and walked away. (Yes, too many people do it that way!)
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I recently poured concrete on an unfinished part of my basement floor. Shortly, after the job was finished, I encountered wetness on the floor when ever I sat an object down. I am baffled as to why this is happening. Has anyone come across this problem? Do you know of any chemicals on the market to help us? What would you suggest?