Moisture collecting on garage floor?

[mtlogcabin]

SFR with attached garage located in Little Rock AR area.

On humid or rainy days with the garage closed moisture will accumulate on the garage floor over night. It is enough you can squeegee it out the door. I assume it is coming up from under the slab. There is also a tornado shelter within the garage and water will come through the wall on the garage side (from under the garage slab) not the exterior side. They have had a lot of rain and I am thinking maybe high ground water or possible water running through the clay soils under the garage. The finished floor of the house is a slab that is about 12" above grade at its lowest point with no signs of moisture there.

I am looking for any suggestions on what the cause may be and possible solutions

Thanks

 

[steveray]

6mil VB under slab?

 

[mtlogcabin]

House was built about 7 years ago in an area with no permits or inspections by an owner/builder (school teacher) so I doubt there is a VB under the existing slab.

 

[cda]

I have seen enclosed concrete slabs with moisture like that

I thought it was humidity

 

[cda]

I have seen enclosed concrete slabs with moisture like that

I thought it was humidity

Any other houses nearby???? Do they have the same problem???

 

[north star]

* - - - - *

An accurate determination of any possible high water

table sources flowing or simply rising to the surface

would be a good first choice, or in conjunction with,

...a determination of any ground water sources flowing

underneath the slab.

This doesn't sound like humidity to me!

A possible fix could be to install oversized, perimeter

french drains to catch the water before entering

[ seeping in to ] the garage.



* - - - - *

 

[Papio Bldg Dept]

Step one, visit Does Eat Place down on Markham and Ringo. Step two, order the steak and shrimp (salad is for the tourists). Step three, consider condensation from temperatures dropping and humidity rising to the dew point. This is common in colder winter and spring months where the soil beneath the floor cools, or remains cool and the warmer moist air condenses into a wet floor on a warm day (i.e., after a lot of rain). THere is not way to avoid this, short of a radiant heated floor to counteract the physics of condensation, and it is a common problem in the area you are talking about.

 

[mark handler]

Coat the slab with Xypex waterproofing it is resistant to extreme hydrostatic pressure.

http://www.xypex.com/products/products.php

 

[peach]

if it's unconditioned, it's probably vapor coming up thru the slab, not condensation (atmospheric pressure, not hydrostatic pressure drives the train).

 

[Mark K]

I have seen reports of tests that indicate that the concret is not that permiable. My bet is on condensation.

You might ask what is driving the moisture through the slab if that is what is happening. If the air is humid it would take a greater pressure or difference in vapor pressure to force the moisture through the slab. If this was the case I would expect more of a problem if ther was less humidity in the air. I also would expect a very high water table.

 

[brudgers]

House was built about 7 years ago in an area with no permits or inspections by an owner/builder (school teacher) so I doubt there is a VB under the existing slab.

The slab of an unheated garage is not an element of the thermal envelope and therefore does not require a moisture vapor retarding barrier - though it isn't worth the money saved to leave it out.

 

[tmurray]

The slab of an unheated garage is not an element of the thermal envelope and therefore does not require a moisture vapor retarding barrier - though it isn't worth the money saved to leave it out.

We require them in Canada for radon gas control within the house, but for whatever reason most people put them under the garage slab as well.

Unless there are openings in the concrete chances are you are looking at condensation. If the slab is higher than the exterior grade then it can't be hydrostatic pressure because concrete isn't that permeable. There is an area outside of my jurisdiction that people have built in a flood plane decades ago. They quickly learnt that once the ground water level gets to the basement windows (about 5-6' higher than the slab) they have to open the windows to let the water into their house to equalize the hydrostatic pressure or the water below the slab will kick it upwards. That would tell you exactly how permeable concrete is

 

[steveray]

Detached, unheated, and not likely to be heated......just doesn't happen here.....plastic is cheap......

R506.2.3 Vapor re tarder. A 6 mil (0.006 inch; 152 μm)

polyethylene or ap proved va por re tarder with joints lapped

not less than 6 inches (152 mm) shall be placed be tween the

con crete floor slab and the base course or the prepared

subgrade where no base course ex ists.

Exception: The vapor retarder may be omitted:

1. From garages, utility buildings and other unheated

accessory structures.

2. From driveways, walks, patios and other flatwork

not likely to be enclosed and heated at a later date.

3. Where approved by the build ing official, based on

local site conditions.

 

[DRP]

Tape a square of plastic to the surface of the floor. Come back during a wetting event. No water under the plastic... condensation is the culprit. Water under the plastic... rising damp.

 

[gbhammer]

Tape a square of plastic to the surface of the floor. Come back during a wetting event. No water under the plastic... condensation is the culprit. Water under the plastic... rising damp.

Now that there is some think'n

 

[David Henderson]

Don't know how high water table is but the water may be entering at the joints of the slab and stem wall. takes a lot of water to penetrate a slab.

 

[JBI]

What kind of ventilation does the garage have? When my Mother-in-Law moved into her new home (12 years ago...) she had a huge moisture problem in the garage. After checking the peak and observing the sheathing going all the way to the ridge board, I had her call someone to cut it back and reinstall the ridge vent and cap. Problem almost immediately went away.