moisture on concrete floor - chicken or egg?

[CT2012]

my detached garage gets some pretty moist/damp surface in spots depending on severity of rain. had planned on doing the floor with mud & porcelain tile as final step to establish a moisture barrier (as well as to be decorative & useful).

just finished framing, insulating, etc. the garage. now doing sheetrock (greenboard will be on walls). i used pressure treated 2x4 for the bottom plate and blocking between studs. cinder block walls, by the way, have 3/4" foam r4.5 vapor barrier and one very thick coat of dry-lok.

am now wondering if i should have done floor first. i figured/guessed that using ramset into porcelain tile with the bottom plate would've resulted in a lot of cracking of tile, which would've been a nightmare to repair and would've slowed the process considerably.

it's raining now and i'm seeing moisture spots pop up underneath the bottom plate in a few areas. my main concern is moisture eventually creeping up from the bottom and finding is way into insulation, etc. etc. am i worrying about nothing, or is my strategy ok given the circumstances?

opinions welcome. thanks.

 

[slickgt1]

You need to look at exterior drainage. First check that water is getting away from the foundation of the garage. Then start tiling.

By the way. I attached a lot of stuff, cabinets, pipe covers, other stuff through my tile. Only thing is, you have to drill the tile first. Nothing cracked. Destroyed a few drill bits though. Surprisingly it is easier to drill concrete or brick.

 

[CT2012]

thanks slick. the detached structure is almost on a mini-hill, sitting about 2 feet higher than yard (it slopes). just can't figure out where the dampness is coming from, it's a bit of a perplexing situation. in theory, i should have great drainage.

 

[slickgt1]

How is your roof drainage? Where does the water go from the roof?

 

[Spencyg]

I have the same problem with my slab. The concrete was never sealed and when it is very humid out or has been raining, the floor will get physically wet in spots. What is unusual is that not ALL the concrete reacts this way, just maybe 40-50% of it. It bugs me to death, but I don't think there is anything I could do to alleviate it. Fancy floors wouldn't work in my shop since I do lots of welding and have 15k lbs of machinery sitting on the slab.

Interested to see what your eventual solution to this problem might be.

 

[jwhcars]

I had a garage on the side of a steep hill. The up hill side and corners would get wet. There where drain pipes installed when it was built but since it didn't appear to do the job I trenched farther up the hill. This worked to get rid of the water. The second row of drainage pipe I had the exit slope away and down hill from the garage. The exit was above ground so there would not be anything to prevent drainage.

 

[CT2012]

in my neighbors' yard.

kidding, but not really. i've got gutters on it, the downspouts have an extension at the bottom that pushes the water away a good 3-4' from the already sloped foundation. the detached garage is like a little castle on a hill... after a particularly heavy soak, it invariably leaches into the neighbors' yard.

How is your roof drainage? Where does the water go from the roof?

 

[Tim The Tool Man]

Do you have a metal roof? might be leaking into the hollows of your block or stud cavity. One or two loose screws is all it takes.

I have a similar issue on the uphill side of my garage (I'm at the base of a small mountain). I am going to eventually end up having to put a sump pump pit in with drainage tile to fix the problem. Just not on my to-do list yet.

Might want to look at the outside where you see water coming in. Is there dirt at or above your floor level? If there is then I recommend that you remove it and pitch the grade away from your building.

 

[CT2012]

no dirt at grade level, and it's a plywood w/asphalt shingle roof w/no leakage.

my only guess is that at the driveway side of things (which is accessed from the street), the garage entrance sits at the bottom of a relatively gentle slope of probably a foot and a half or so over 30 feet length, and whatever's draining under the driveway doesn't disperse quickly enough to the other 3 sides of the garage.