Porcelain over weeping garage slab

[saxman2u]

It was humid today here in Austin, TX. Trace of rain (.01 inch) and the slab is darker in several spots, no puddles, just darker because of the moisture. The slab is 24x40. The back of the slab is about 3 feet from the ground. The slab was fine yesterday, but no rain today, just plain humid. The slab weeps like this maybe 5-10 times a year.

If I install porcelain tile over this slab, with the moisture transfer to the tile as well? Would I be better off to install Ditra in this case to limit the weeping?

The slab is 20 years old and the PO did the work, so, who knows what was done. Live outside of Austin so probably not up to code back in the 90's in Hays County.

I am planning on using PEI 4 or 5 rectified tiles with Flexbond.

Thanks for the advice,
-S

[John Bridge]

Hi Scott, Welcome aboard.


Porcelain tiles, by U.S. standards, are impervious, and water will not pass through them. Water will come through the grout, though, and the water could cause efflorescence in the joints. Ditra may be your answer.

And are we sure this is water coming up through the slab and not condensation? In that case, all bets are off.

[saxman2u]

Thanks for the quick reply. Making sure I understand, "all bets are off"...So, are you saying if it is just condensation, I should be ok not to install a vapor barrier?

Since it has not rained, are you doubting it is water coming up from the slab then?

[cx]

Welcome, Scott.

What you're describing sounds like condensation to me. Nothing you put over - or under, for that matter - your slab is gonna prevent that when the conditions are such that the air in contact with your concrete reaches its dew point. Gonna get wet on top.

Chances are you've not got a vapor barrier under that concrete, either, and that you will certainly have some significant moisture vapor emissions during some relative conditions between top and bottom.

And your PEI reference is a bit out of date and no longer used in the tile industry. But it does indicate that you intend to use a glazed tile and I'd suggest you might not wanna do that. Any tile you put on that garage floor is gonna be slippery when it gets wet, but a glazed tile is gonna be slippery even when you're just thinking about it being wet.

My opinion; worth price charged.

[saxman2u]

CX,
Thanks for the info. I will look into non-glazed tile, rectified though.

As for the condensation, since I can't get rid of it, that will come up through the grout on these more humid days, right? If so, would it be better to go with an expoxy grout?

-S

[cx]

Condensation will not "come up through" anything, it will appear on the surface where the dewpoint of the surrounding air is reached.

To prevent it, or to make it disappear, you need to either raise the temperature of that surface or lower the relative humidity of the surrounding air.

You may prefer epoxy grout in your application, but it won't change anything in relation to your condensation issue. It may slow the moisture vapor emission rate if you also have that problem, and that could be a factor in your choice of bonding material.

My opinion; worth price charged.

[saxman2u]

CX,
That makes sense. Thanks for the information. I was planning on using Flexbond for adhering the tiles to the slab. I know expoxy grout is more labor intensive, I just thought it would not corrode if it got wet over time.

What would you do in this situation?

BTW, I am planning on heating/cooling 1/3 of this area because the workshop is another room in the garage. This will help with moisture control.

What would you do in this situation?

-S

[Davy]

Scott, check the coverage on the epoxy grout too. On a floor that big, it would cost a lot more than regular sanded grout.