moisture problem in heated attached garage

[Gary_C]

kevjay

There are some assertions that are accepted as facts, even in scientific, engineering, and construction work, even though they are not absolutely true.

One is that the earth is round, nonwithstanding the claims of the Flat Earth Society. That assertion is not completely true as the earth bulges slightly at the equator. Also if it was perfectly round you should be able to fly from New York to LA at 5000 ft elevation without hitting anything.

Another is that liquids are incompressible. That is accepted as true in all scientific and engineering work, but liquids can be compressed slightly at very high pressures.

Another is that water expands when heated and shrinks when cooled. That does not apply when water freezes.

Another is that concrete is one of best non porous construction materials. As you have pointed out and I have agreed, that claim is not absolutely true. However it is still used in structures like holding tanks and dams where it is absolutely essential to use a material that is non porous.

So for the question posed by sbishop about his garage and the moisture present, that concrete floor can be considered non porous.

[TexasTimbers]

I was simply trying to stay within the confines of the issue.

I think that it is pointless to continue beating it to death so I will concede that the earth is an oblate spheroid - you are right about that.

[Furby]

Sorry Gary, I don't agree.
Simple definitions of porous:
http://www.google.com/search?hl=en&q=define%3Aporous

If you have ever busted open a piece of concrete, you would have seen the pores.
Thus concrete is porous, no way around it.
Heck, by definition, metal can be porous and still hold water.

Now in the case of Mike's cistern, I'd be willing to bet that it has been hand finished with cement.
I had several such cisterns, mine were made of brick with lining of cement that held in the water.

I just gotta point out that they call the Earth round, not "perfectly" round.
Liquids under extreme pressure compress only because the small amount of oxygen they contain is squeezed out.
Water shrinks when cooled, once it starts to become ice, and it changes from a liquid to a solid..... it's no longer water.

[wiam]

I have been inside of a hydro dam.  Do not try to tell me that concrete is nonpourous.  The water just runs through that place.  Kind of freaky at more than 100' below grade.

Will

[bitternut]

I have a concrete floor in my garage that has no insulation under it. It sweats like crazy every spring when the weather starts warming up. My barn also has a concrete floor and it never sweats. It has 2" of rigid foam under it. I once owned a house that had a cistern with a block wall and cement waterproofing. Never leaked a drop or showed any condensation. Don't know what this proves but just thought I would add my experiences with concrete products and moisture.

[SwampDonkey]

Mr Bishop, You could search the knowledge base of the Cement Association of Canada.

http://www.cement.ca/cement.nsf

[Gary_C]

Furby

You win!  ;D

My truck is loaded and ready to head north on I-35. I think the Burlman is getting anxious for me to get done and I can't pick up any wood here. I just hope that all that water that soaked into the concrete on I-35 does not freeze tonight as it may expand and break up the concrete. If it does, I may have to walk home for Christmas.   :(

[bitternut]

Don't worry Gary we coat the roads in the North with salt every winter so that they don't freeze.  :D  :D

[mike_van]

Furby, i 've seen the little holes in the concrete, they call it "air entrained"  It make it tougher they say, more resistant to chipping, etc. out in the weather. I don't know that the holes connect though? Wouldn't seem to be very strong if they did. Concrete you mix yourself won't have these holes unless you add this "air entraining" stuff -  So, here's another odd one - Every rock & boulder i've ever split is wet inside - damp anyway, how did that get in there? 

[SwampDonkey]

Yes, on that site I posted, if you go into the knowledge base there is information on it. Select from the drop down list in there.
Here's a few snippets I reamed from the site:

concerning air entrained concrete
Air content decreases with temperature

More air, less strength

More water, less strength when setting

Improves workability

Requires less water than non air entrained cement

Improves freeze/thaw resistance

Those bubbles and air voids in concrete are from entrapped air, some mixtures actually repel water (anionicly charges)

Water tightness depends on the amount of water in the cement when mixing and curing.

Other snippets:
"Sound, dense concrete made with a water-cementing materials ratio of less than 0.50 by mass will be watertight if it is properly placed and cured."

"Dampproofing admixtures are sometimes used to reduce the transmission of moisture through concrete that is in contact with water or damp earth. Many so-called dampproofers are not effective, especially when used in concretes that are in contact with water under pressure."

"The amount of water that will evaporate in air at 50% relative humidity is about 1/2% to 3% of the mass of the concrete, depending on initial water content of the concrete, absorption characteristics of the aggregates, and size of the structure. The absorption of fly-ash concrete is about the same as concrete without ash, although some ashes can reduce absorption by 20% or more."

[Ironwood]

Boy you guys are a real ball!! Let's seee........... I assert that .......

Oh, we don't need anything else to get your ire's up.

             Reid

[SwampDonkey]

If I was gonna call to ask, I'de talk with the guy whose business it is to supply concrete to the building contractors. Some contractors know about concrete (usually trained engineers), but a lot don't and I have lots of concrete evidence to prove it.  ;D  :D :D :D

[Furby]

Like that wall of yours Donk? ;) ;D

[SwampDonkey]

Yip, along with the garage floor.  :

[slowzuki]

Back to the garage problem, your drywalling and car snow is bringing in fair amounts of vapour and even you are by breathing and opening the door to your house.  The house are is warm and wet compared to the garage.  Swampys church is having moisture from the people breathing condense on the windows.

The windows are acting as dehumidifiers since they are the coldest objects in the room.

Options to fix the problem:
1. Turn the heat up to match the house - this would help but not completely cure the problem.
2. Install heat recovery air exchanger - expensive since you are only heating to 5 C so you are not trying to save much heat
3. Install regular air exchanger - this is basically an open window with fan.  Can be hooked up to a humidistat to regulate humidity
4. Run a dehumidifier - they don't work efficiently near freezing temps.

The goals you have to achieve is dump moisture out of your garage or make it hotter so the air can store a lot more moisture.  Even making it hotter will only work so far, mostly it helps by driving the leakage of air through the walls much stronger resulting in more air exchange.


These solutions don't always work the same in a basement in the summer in NB because the air is really wet out side and the basement is really cold.  If you put more outside air into a basement during summer more water will condense out of it.  In a basement here you have to dehumidify or use a heat recovery ventilator that can use the cold air leaving the basement to dehumidify the warm wet air coming in.  The other option is to heat the basement even in the summer, works best with infloor heating.