Moisture Test - Garage Floor

[Wile1Coyote]

Was reading the Ultimate Garage Handbook last night wherin they describe a test to figure out how much moisture is flowing up from under your garage slab.

You take a 6'x6' sheet of poly and tape it down to the floor, wait a few days and see how much moisture gets trapped under the poly. This helps you figure out whether you can paint or tile the floor. Pretty cool, only I am not sure if this is a good time of year to try that test. It being winter still here in the mighty motor city I am lucky to get above freezing during the day which means there is less moisture in the ground anyway right?

Do you guys think it would be better to wait till spring when the ground near me is the wetest or is that a bad test too? Should I wait till summer? :headscrat

Thanks in advance!

[GearHead_1]

Just guessing here but I would think that you would want to see the results in the most severe condition or when the condensation would be the greatest. If that means when the ground has thawed then that would likely be the best time to check. I think your thinking is correct.

[casaleenie]

What's an acceptible level of moisture?
How do you gauge what's under the plastic?

[Luckydevil]

What's an acceptible level of moisture?
How do you gauge what's under the plastic?

http://www.rustoleum.com/EPOXYShield_Tips.asp?TipType=I#WNTA

as per Rustoleum... "Moisture in the concrete - Apply a 2' x 2' sheet of plastic (such as a heavy-duty garbage bag or 1 gallon plastic storage bag) to an area of the surface to be coated. Tape down the edges with duct tape and allow to sit for 24 hours. If water droplets appear on the bottom of the plastic or if concrete appears wet (darker in color), moisture is trapped in the concrete and the surface should not be coated."

[Craig Balzer]

I found this on the net -- here: http://www.rona.ca/webapp/wcs/stores/servlet/ContentServlet?assetId=8709&langId=-1&parentAssetId=41&parentAssetId=6#129456

If you discover efflorescence salts (white powder that sometimes forms on concrete surfaces), generously swab the affected area with a diluted solution of 1 part muriatic acid and 1 part water, scrub vigorously with a broom, let stand until the “bubbling” effect dissipates (do not wait until the solution is dry!), rinse thoroughly with clean water and let dry. Note: Efflorescence salts are caused
by excessive humidity. If present, it is important to determine the cause of the humidity and eliminate the problem.

To perform a humidity test, the concrete must have been dry for 72 hours and the temperature of the concrete must be above 60ºF.

Using masking tape to hold them in place, tape down four or five 12 in. x 12 in. (or larger) squares of plastic sheeting (polythene) in different locations across the floor, including the area where you found the efflorescence salts. Because
moisture movement tends to vary depending on the temperature of the concrete, you must leave the squares in place for 24 hours, if the ambient temperature in the garage is higher than 68ºF; or for 3 days, if the temperature is between 41ºF and 68ºF. Do not perform the test if the temperature is below 41ºF. When the appropriate amount of time has elapsed, check to see if there are any droplets of condensation under the plastic film. If you discover condensation, find the source of the humidity and correct the problem. Failure to do so will probably prevent you from painting the garage floor. If there are no droplets under the plastic sheets, the floor is ready for the painting process.

Hope this helps

[dink]

Well lets say you do have a lot of moisture after this test.....what are some good ways to seal it so you can move onto what ever your going to do??

[Craig Balzer]

Dink

To answer your question let’s go back to the source that started this discussion: The Ultimate Garage Handbook:

According to the author:

Page 19:
“If you find any moisture, your flooring choices are limited. Paint is simply out of the question. Installing vinyl tile will require the construction of a sub-floor under the tile. Even carpeting is questionable since the moisture will attack the carpet backing.

Page 26, caption to photo
“If you have to put down a floor in your garage because of ground moisture migrating through the concrete here is the correct sequence: the asphalt underlay goes down first, followed by a heavy plastic sheet, ¼-inch exterior plywood goes on top of the plastic; then start with your tile.”
The photo shows a staggered view of the four layers. The first three (asphalt, plastic and plywood) are very thin. The asphalt looks to be about the thickness of a sheet of paper and the plastic is transparent -- no further specs are mentions about the thickness of the plastic. As mentioned the plywood is 1/4". Then the tile du jours

Speaking of this book, I can HIGHLY recommend it. I happened across it when I was looking for something to read for a l-o-n-g flight (Denver to London to Dubai to Kabul). It is excellent. It is the third book I bought in my getting educated process before building my Garage Mahal. I read it thee times during my flights (the 21 hour layover in Dubai was useful for the underlining time).

Ultimate Garage Handbook
Richard Newton
Motorbooks
ISBN: 0-7603-1640-6

Craig

[springer69]

I have 2 small spots maybe 2 inches square that have the white powder which I assume is from water. They are near the centre pressure crack. Can anyone tell me if I should worry about this? I want to epoxy this week.
springer69