I have a new home that we moved into about 4 months ago. REcently I started to finish off the basement and I found moisture and frost behind the insulation in the framed up walk-out part of the basement. What can I do to remove this and how do I prvent it form coming back? I have been running a Dehumidifier for 2 weeks now and there is very little moisture int he air, it is also December and very cold outside.

Dampness on the basement walls of a new home is very common. When pouring floors and I assume you have a concrete poured wall as well they use a LOT of water to mix the cement. It takes almost a year for this to dry out. My suggestion is not to finish until then. Any moisture that is trapped behind the insulation or behind finished walls will only lead to mold issues later on. Be sure that your keeping a space behind the walls for air to move.

Look into a Humidex system for the basement to remove the humidity. It cost a little more to install but will save you a lot in operation costs when its needed.

As far as the frost. Are you sure that is what it is? If its puffy like cotton candy or a white powder its not frost. Its effloresence. You normally see this near the floor level and in corners forming a x-mass tree shappe. This is A byproduct of the salts and minerials that deposited on the surface of the cement as the water evaporates out of the cement or block walls. If it is frost you have a heating issue that needs to be addressed. Frost only forms when temps are 32 degrees. If your basement is that cold behind the finished walls you will have issues with frozen pipes and mold.

Is the moisture is wet? Or does it just feel damp? Contact your builder. You should not have ANY wet walls at all. Regardless of what he may say. New homes should have a warranty on moisture such as this and typically the builder must warranty it from happening.

DO NOT paint or let them paint any water proofing paint on the inside of the cement or block walls to stop the water entry. This will only trap the dampness in the cement and through vapor pressure eventually push the paint off the walls or cause other issues with them.


Do you have a humidifer on the heating system? The new units they install are often capable of putting several gallons of water in the air in a very short time. Quite often they set them much to high when they are installed. The end result is excessive moisture that collects on any cool surfaces and condensate forms. Check if you have one and set it down. New homes unlike older ones do not require as much humidity in the air due to the tighness and energy efficency of the house. They often become to humid which leads to other issues.

Thank you very much for the info. I have been running a de-humidifier and it has pulled very little moisture out of the air. The room temp. is currently 60 degrees and only drop s to 58 at night. I have some moisture on the sills above the concrete walls and below the first floor. The only other moisture collecting is behind batt insulation in the walk-out area. It is not a sdrastic amount however in small spots it has produced mold.

Sounds like you may have either a non-existant or an improperly installed vapor barrier.

Thanks, do you think I should apply a 4 or a 6 mil barrier. I live in the NorthEast where temps fluxuate a lot form winter to summer. I have been drying out the insulation adn the walls for about a week now, do you think I should invest in a moisture detector before I re-install the insulation/barrier?

There are a lot of differing opinions on how to best finish a basement. I'll give you mine, keeping in mind that the next guy may tell you a totally different story. My firm belief is that fiberglass insulation and plastic vapor barriers have no place in a basement. If you are going to finish a basement wall, use foil faced rigid insulation glued directly to the concrete wall, make sure to seal the joints with spray foam and then tape with house wrap tape.
Then build your stud wall (preferably steel studs, if not make sure the bottom sill is treated) against the insulation, but put no insulation in the stud cavities at all. The foil face of the insulation will act as your vapor barrier and is far superior to any plastic you will use. The reason we put the insulation on first and not between the studs is because of this way creates a more effective continuous vapor barrier.
Like I said, this is my preferred method - if there is a better way, I'd love to know about it.

Edit: Incidently this is one of the reasons why we only use ICF forms for our new houses, it puts the vapor frost point on the outside of the wall, not the inside.

Thanks Jay, I am using a 3 1/2" Foam insulation on the concrete walls. As for the walk-out section of the basement it is all 2X6 framed construction with insulation batts on the inside and a poly vapor barrier over that. This is the area where I founf the moisture to be.

If the moisture is on top of the poly (heated side) then two things are of concern.
1. excessive humidity levels in the house.
2. Insulation not properly done where condensate is forming allowing cool air to reach the vapor barrier causing the condensate to form.
The temp has to drop to the dew point to allow condensate to form. The dew point is related to the amount of moisture in the air. The more moisture in the air the less the air or surface temps have to drop before condensate forms. Also the higher the R value of the insulation the longer it takes the cool side to reach the dew point temp in which the condensate will form.
If the moisture is behind the plastic then the reverse is happening.
The air temps in the finished side is dropping down more then the exterior side causing the condensate to form on the inside. If that is happening then there is excessive moisture trapped behind the finished wall. You need to wait until the cement dries out. Unkess you use a system like I suggested in prior post.

I agree with Jay about the method of insulation however. A lot of contractors fail to realize that the poured cement walls used today hold a great amount of moisture and it takes almost a year and sometimes longer for this to properly dry out. Simply fastening this foam to the walls traps this moisture which in turn causes mold to develp behind the foam. Not as bad as you would see if it was the blanket insulation but will get it non the less. WE had homes in which the blanket insulation was so wet that it started dripping water when we pushed against it.
Be sure your insulation is complete. No gaps or openings. Be sure your vapor barrier is sealed tight. No holes. Seams need to be taped properly.

Using four or six mill plastic is really not a big issue. Ideally the thicker the plastic the better it performs. Both for strength when applying and for vapor resistance. I would purchse a mositure meter and check the studs and wall to see what you have. It should be in the north east around 12% But compare it with areas in the house where you know things are dry. Use that as your constant. If yoru getting readings in the area of 20% things are not dry enough and mold can develop.

When you say the areas in which have had visual moisture you have had mold grow. How do you know its mold? It is very difficult for mold to grow on cement, unless its painted or very dusty and dirty. Remember mold needs a food source in which to grow. Cement offers very little in which to eat. What exactly are you seeing and where is it on?

quote:

Originally posted by The Home Care Club LLC:
A lot of contractors fail to realize that the poured cement walls used today hold a great amount of moisture and it takes almost a year and sometimes longer for this to properly dry out.?

Agreed. We tell our homeowners to wait at least a year to finish the basement for this very reason. For homes who want us to finish their basement (without ICF forms), when gluing the foam to the concrete - we always run the glue bead on the foam up and down instead of side to side. This is more of a precautionary measure, in case some moisture or vapor does come from the concrete, it will allow it to run down the wall rather than get trapped on a horizontal glue bead and sit there. Now I'm not talking the a lot of water from rain or high water tables or whatever. I'm talking vapor condensing against the back side of the foam. Small amounts at a time until the concrete cures.
On a side note, this is one of the reasons I like foam with foil facing on both sides, it prevents moisture from getting inside the foam and sitting there. Better to have small amounts at a time drain down to the floor than have it build up over time and sit behind a wall.

Thank you both for your replys. I do not have moisture on the concrete, only the framed part of the walk out in the basement. I do think whats there was from the cement curing over the past couple of months and finiding its way between the insulation and the ext. walls. Any suggestions on how to remove this and proceed with finishing the basement off?

In California basements are not a big option but we do have issues with CMU's (concrete masonry units) and concrete retaining walls producing efflorescence. I have used a product called DRYLOCK which paints onto the interior surface of the wall and reacts chemically with any moisture in the wall creating a seal. Take a lok at their website and download the brochure. It has great information on when, if and how to apply.
http://ugl.com/drylokMasonry/masonryWaterproofer/extreme.php

Regards,

Tom Judt

Drylock and other products like that work well.
But and its a BIG but. People use this product as a water proofing system. Although it will hold water back, for a while. It fails to allow the cement to properly breath and dry thus causes hidden damage behind the finish. The new walls MUST breath for at least a year before any applyed sealant is used.

Kory, is the framed wall inside the masonary wall? Or is the framed wall part of the exterior framing of the basement? Does it have siding on it on one side?
If the framing is inside the cement walls then the excessive humidity trapped behind the wall facing the cement side is cooling down and allowing condensate to form. You need to ventilate behind the finished walls to allow the moisture to escape.