My Mystery Guest...Moisture

[nolimits76]

I walked into the garage to discover this (see pics below). We moved in the house last summer. It's rained before. I noticed it once but thought I was losing my mind.

Just to be clear, no one was toying around in the garage. My wife goes to work before I do. She walked from house to car and left. I did the same thing, minus the few seconds I took the pictures. When I backed out, I noticed I had "tire tracks" similar to my wife's side (again, I didn't back up and pull back in). Normally my concrete looks near perfect.

It was raining on my home last night (about 9pm). I presume it rained while I was asleep as my driveway and the streets were wet.

Can someone tell me what is going on? And how do I fix it? I would like to do some sort of flooring in the future, and leaning towards epoxy, but this has me worried.

I would assume it's moisture wicking up from underneath. I'm not sure why though. To my knowledge, I don't have any drainage issues. I live in OK which can be humid, but it didn't feel excessively humid today. Below are stats from weather.com.

- Temp 66* (feels like 66*)
- Wind SSW @ 26mph (gusting to 31mph)
- Humidity 74%
- UV Index 0 Low
- Pressure 29.4 in
- Dew Point 57*
- Visibility 10 miles

 

[CheckeredFlag]

Do you know if there is a vapor barrier ?

Has it recently been very cold + now warming up (so it's more like condensation on the floor) ?

not sure that paint / concrete sealer will fix this, but would like to hear others responses

good luck

 

[LegacyIndustrial]

Agree with Checkered, looks like a cold floor and warming temps.
A plastic test is in order.

 

[Shea]

The dew point and temperature of the concrete are the key in determining if it's condensation. If the surface temp or your concrete is below 57 degrees, then you can easily have condensation with a relative humidity of 74%. This can happen if your slab is cold soaked from longer cold temperatures and then you have a sudden (relative) warming of the air.

If you suspect condensation, dry one of the wet spots real well and then tape down a 12" square sheet of plastic (well sealed) to sit over night. If the next morning it is wet around the plastic but not underneath, then you have condensation. If it is wet underneath as well, then you have moisture coming up through the slab.

 

[nolimits76]

No idea if there is a vapor barrier. The house was pre-existing when I bought it.

How do I check the temperature of the concrete floor? My door opener has a temp gauge on it, but it sits about 5' above ground level and is mounted to drywall (other side of mounting location is my laundry room).

Weather has changed in the last week or so. Here is what weather.com is officially reporting for month of February.

Date = Hi Temp / Low Temp

2/1 = 33* / 28*
2/2 = 29* / 14*
2/3 = 39* / 9*
2/4 = 34* / 27*
2/5 = 26* / 11*
2/6 = 19* / 8*
2/7 = 27* / 15*
2/8 = 32* / 25*
2/9 = 34* / 26*
2/10 = 28* / 19*
2/11 = 37* / 16*
2/12 = 48* / 16*
2/13 = 60* / 28*
2/14 = 59* / 34*
2/15 = 67* / 26*
2/16 = 65* / 32*
2/17 = 65* / 44*
2/18 = 73* / 38*
2/19 = 69* / 36*
Today, 2/20 = 67* @ 8:52am / 52* current / 31* projected

 

[nolimits76]

A plastic test is in order.

If you suspect condensation, dry one of the wet spots real well and then tape down a 12" square sheet of plastic (well sealed) to sit over night. If the next morning it is wet around the plastic but not underneath, then you have condensation. If it is wet underneath as well, then you have moisture coming up through the slab.

I presume these are the same tests? Will a trash bag and duct tape work? I can do this tonight when I get home. How long does it need to set?

 

[JakeKohl]

Honestly, with the fast warming trend, it's extremely likely that it's just condensation. You can check the slab temperature with a point and shoot temperature gauge...they usually come with a laser pointer and you can get a cheap one for $20 - $30.

My back porch consists of a great deal of concrete. When we have these changes from bitter cold to humid warm, it can sweat for DAYS to the point that water is running off it.