I'm not TomVan (see 'Lost Studios in Portland' thread); he had posted here with respect to my questions on the basement concrete...
I may not have any answers for you, but I do have some comments...
peteys wrote:
I have a new house with poured walls, footing drains and "rubberwall" sprayed on the outside of the foundation. But last year before I bought my dehumidifier, there was water on the floor on the inside corner of my basement, sweating pipes and such. With the humidifier there this year, there is none.
I'm sure that you also have a vapor barrier beneath the slab?
Is there also a capillary break between the footing and the walls?
Was this condensation present mainly only in the warmer, humid summer months?
Do you have rigid insulation on the outside or inside of the concrete?
Anyway, as you probably obviously know, when the warmer, more moist outside air makes contact with the cold surfaces of the concrete, the moisture condenses on those surfaces, which is why you bought the dehumidifier...
Interestingly, I have read in a few places that having a dehumidfier can actually 'pull' vapor/moisture from the outside, through the concrete, due to an increase in gradient between the moisture on the outside and inside.
Supposedly, this can increase efflorescence and spalling...
(I think the point of this idea is mainly that you should additionally pursue other means to decrease moisture from GETTING into the basement, but not to avoid the use of a dehumidifier).
peteys wrote:
My questions is what effect does condensation play when finishing the basement floors and walls on the unconditioned space. ie. the air space between the inner wall and outer concrete wall and also the floor, assuming I put some type of laminite down.
Ahh, this has been a question for me as well...
From what I have learned, there are 3 moisture sources to consider here: first the condensation FROM the air, second the vapor coming through the concrete INTO the air, and third any seepage that would occur due to rainwater, groundwater, or surface runoff (that might overload or avert your drainage tile system).
Even though you have some sort of dampproofing or waterproofing on the outside of the foundation, my guess is that there would be still some vapor movement through the concrete and into the basement... of course, I really will defer that to TomVan, since he is the expert here...
But, my point is -- from what I have researched and read about -- no waterproofing system seems to be, or remain, 100% competent forever and/or under all situations.
(Concrete can crack and settle, drain tiles and pump pickups and discharges can clog, outside grading can change, gutters and downspouts and pump motors can fail...)
[For example, a friend of mine has a house, built in the late 90's; this was a construction that utilized all the latest (radon systems, sump, draintile, insulated, etc.); the concrete wall has already developed a full, separated crack from the top to the bottom...
In contrast, my house, made in 1959-60, has never had any such cracks in the basement walls (I’ve looked at the walls very closely) yet it has little or none of the 'modern' things that my friend's house has (BUT of course, that doesn't mean that we have never had any water issues here)... on the other hand, I do have hairline cracks in the floor slab – in the areas where it had been dug for the sewage service (house originally had a septic tank).]
NOW, about the 'dead air' spaces and vapor moisture....
It seems there are things here:
One says that you want to allow moisture to travel IN through the concrete and into the room;
The other says that you want to concern yourself with preventing the inside moisture from reaching the concrete walls...
Actually, still another seems to say that both are to be considered...
The problem is, it would seem that you can't use true vapor barriers and account for both situations -- at least if your dead-air space is 'locked-in' everywhere.
If you use a vapor barrier under the inner-wall surface, you will block condensation from the inside air on the concrete wall surface;
But could that barrier block vapor coming through the concrete from dissipating into the room -- and, IS this a problem if there is a sufficient air gap, or if you are fire-blocking from the above floor, can this allow vapor to vent somehow, somewhere and still maintain isolation?
I tried to find a paper I had read that talks about the problems with 'overuse' of vapor barriers, and supports the use of vapor retarders... not just in the basement, but in other areas of the house as well -- particularly in mixed-climate regions...
So, the concept is to slow the vapor moisture migration and not to stop it.
This may be the best compromise, I don't know...
But TomVan had recommended that I use a product on the concrete floor that was a cementitious 'moisture reduction barrier' or MRB, that is made by Mapei.
This reduces vapor through a slab a great deal, but still allows a certain percentage through in order that it doesn't 'build up' below that surface and ultimately separate it from the concrete.
On the walls, he recommended something like Thoroseal.
Of course, I believe he also said that any (non-moving) cracks or gaps should be chased, dovetailed, and filled with an epoxy or urethane.
Then again, remember, I probably don't have a vapor barrier below the floor, like you might, nor anything substantial on the outer surface of the walls either... so your situation might be different, and your dead air space 'needs' might then be different.
Whatever you find out, please post about it, so that others (me especially
) know...
thanx,
K
Holy cow!
...that does suck. 
