Is This Slab too Wet for Porcelain Tile?

xand83April 8, 2011

Oye. So, we live in a basement condo. It's completely dry, or so I thought. I'm pulling up the tile in the foyer now. The old ceramic tile was a pain to remove, but around the door, it was a breeze. That's because the thin set wasn't adhered to the slab.

There seem to be several layers of concrete down here. The majority of the condo is one raised slab (higher than the foyer) that has parquet, marble tile, porcelain, and some vinyl. I've seen most of that slab and it was fine prior to putting down a new floor. But this one has me a little leery. You'll see part of it extends to the outside. Now, that is raised from the level that has several drains that have worked well in the last year we have been here. It never floods, but it is raining now and the interior part looks damp.

I want to put some 12x12 porcelain tile down, like we have recently done in the kitchen. Am I screwed? What can I do?

Shot of the entire foyer:

Front door open:

Close-up of area:

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* 1

Roll out waterproofing membrane and cut it to the proper length at the walls with scissors. Repeat this process until the entire surface area is covered with waterproofing membrane.
* 2

Pour waterproofing paint into a paint tray. Use a paint roller to apply a thick coat of the paint over the waterproofing membrane. Cover the entire floor and allow paint to completely dry.
* 3

Determine the layout for the tiles and choose a place to start. Use a notch trowel to evenly spread thin-set mortar in that area, making sure to make the notches even. Spread thin-set mortar with even notches on the back of a concrete tile. Set the tile in place and press down firmly to make sure that the mortar on the tile bonds to the mortar on the floor.
* 4

Use a level to make sure that the surface of the concrete tile is level. If it is not level, use your hands to push on the tile to adjust the levelness. Never use shims or other objects to adjust the level of a tile, because this will cause gaps in the mortar and ultimately lead to tile damage. Repeat this process for every tile. Place spacers between every tile to ensure even grout lines throughout your surface area. To make sure tiles line up correctly, push tiles with a straight edge occasionally to straighten the lines.
* 5

When your tiling reaches the walls of the floor area, you will need to cut tiles to size to fit in the spaces. Measure the space remaining for each tile to be set and mark tiles with the correct measurements. Use a wet tile saw to cut each tile to size and set the tiles in the manner described above.

    Bookmark   April 9, 2011 at 10:20AM
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Okay, if you follow floortech's first two steps, as specified, your install will fail. A sheet membrane needs to be installed properly with the correct adhesive - just laying it out is not acceptable. Additionally, you never, never, never, never should paint over a waterproofing membrane and then expect tile to stay adhered to the paint.

First of all, you need to know if you have moisture coming from below the concrete. Do a moisture test. Clear plastic sheeting, about 2 ft square, duct taped down to the concrete where you suspect a moisture problem. Come back in 24 hours. Is there moisture accumulated under the sheet? If so, you would need to correct the problem causing the moisture or practically any flooring install will fail. It could be, however, that you have had a problem with water coming in through the door, rather than from below. If this is the case, you can successfully install tile with a properly installed waterproofing membrane.

Do your moisture test. Then, to get correct information about how to install tile over concrete, head over to the John Bridge Forum (Google it) and ask how to do it, or just search the forum and you may find your answer. There are actual pros over there that donate their time to help. Let us know what they say. Good luck!

    Bookmark   April 9, 2011 at 9:15PM
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Ditto aliceinwonderland_id
Sounds to me that the OP xand83 knows a lot already.
There is a Mapei product that works a bit like how floortech described it.

    Bookmark   April 9, 2011 at 10:47PM
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Thanks for your help everyone. We perused Home Depot today to see what they had available. I bought a gallon of Redgard waterproofing membrane to be applied with a nap roller.

My hazy plan at this point is to finish removing the thin set that I can get up, Redgard, self-leveling cement as there was noticeable dip in the old tile that was annoying, and then tile. Do you think this will be sufficient? I don't believe the moisture is extreme, just wicking in a few feet from the other side of the door. I've had a piece of cardboard down in the entry since yesterday and it is bone dry. But I might give that plastic test a try too. Thanks!

    Bookmark   April 9, 2011 at 11:06PM
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Redgard, as well as other topical or sheet waterproofing membranes, are for water coming from above the tile, not below, which is why you need the moisture test. Regardless, if you are going to use Redgard, the order should be self-level, Redgard, then tile.

    Bookmark   April 9, 2011 at 11:17PM
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Haha- I'm perfectly muddled right now! Wouldn't a waterproof membrane work both ways? I do see your point about using the self-leveling concrete first, though. It seems like the below thread covers a similar concern, almost.

I have the plastic down now. I'm pretty confident that no moisture will be visible, but we'll see!

Here is a link that might be useful: John Bridge thread

    Bookmark   April 10, 2011 at 12:15AM
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ditto aliceinwonderland_id ;

Terms used are subtle and appear the same or similar, in this field of water-moisture-humidity transferring itself across apparently impervious barriers. H2O is the universe's most solvent solvent, it slips through everything. Not much is known about water and its ability to slide through things. It has been observed in some buildings that had two parallel layers of barriers H2O built up that inside the sandwiched region it became like a container holding standing water. I can hunt down a discussion of this if it's truly required.

For more general reading on membranes search about what is applied to basement walls that leak. That is a common subject. For example, look at the manufacturers' sites and see that they have many products, and often the products are NOT recommended for the other purpose. Either it does one thing or the other.

In many 2nd-floor bathrooms in house structures that leak a lot of air, none of this important. No incoming H2O is present, the stud cavity dries out if there's any wickage, etc, ETc. Your situation is the opposite.

xand83, the thread you linked to starts off by talking about the product. Bad start. Begin with the reality you have in front of you. Understand it. Later, much later, choose product. The thread you linked to talks about applying the product. Not the subject of your focus today. The thread you linked to concludes with a recommendation for a Schluter product; this happens 99.9% of the time in the jb forum in the last ten years. The tilesetting universe's most friendly forum always ends threads that way. Go figure. If you want to discuss alternatives, for a specific need, you may. But in general, if there are alternatives to Schluter products and you want you deal with them, you are gently nudged out. Go figure. If you insist on continually dealing with subjects that you want to deal with, you are forcefully ejected by multiple means of pressure. Go figure. Now, you will get help today from the jb forum on this project that you have begun, but only enough to ensure the prime sponsor doesn't suffer any reputation damage. Go figure.


    Bookmark   April 10, 2011 at 8:01AM
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xand83 - When water comes from the top and hits the waterproof membrane, the force of the water is pushing downward in the same direction the membrane is supposed to go, and does not, therefore dislodge the membrane. Eventually if evaporates back out through the grout. When water pressure is coming from below, the pressure is pushing up, working against the waterproof membrane, causing it to lose adhesion.

davidro1 - You appear to have a personal issue with the John Bridge Forum. Your vitriol is misplaced in reference to the OP's question and only serves to muddy the waters, rather than adding clarity to the conversation.

    Bookmark   April 10, 2011 at 11:45AM
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Avanti Tile & Stone (Stonetech)

Hth~ Do we recommend isolation membranes like Ditra over some other methods at JB Forums? Yes, oftentimes we do...but not because they happen to be a sponsor...we may do so because we find them to be superior to some other methods, and use it ourselves professionally. We have taken sponsored products "to task" on more than one occation and let the chips fall where they may...and no, we don't "force" someone out with a divergent opinion unless they're simply spamming or looking for a fight.

In the provided link, John Bridge ended by suggesting the best water isolation approach, but did not "diss" the fact, supplied a link, should they prefer that option.

If you have a wet slab you can use Schluter Ditra. Cost is much more than RedGard, but Ditra will accommodate the moisture beneath it. 

Don't get me wrong, though, RedGard is fine in most cases.   
    Bookmark   April 10, 2011 at 11:58AM
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Avanti Tile & Stone (Stonetech)

Guess that about says it all......

    Bookmark   April 11, 2011 at 6:27PM
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So, the plastic has been down for almost 48 hours at this point and it is completely dry underneath. Maybe that part of the slab just "appears" to be damp, but really it's fine?

The weekend was pretty much a loss, so I am just now finishing up the thin set removal and I plan to use the SLC tonight. I'm not sure I'm set on using Ditra at this point. My thinking is if the last tile lasted 15 years with no issues, is there any reason to believe this tile job would fail?

    Bookmark   April 11, 2011 at 7:51PM
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Use the correct primer for the SLC or suffer the consequences.

    Bookmark   April 12, 2011 at 8:23AM
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Crap. I don't have any of the latex primer. Neither do any of the hardware stores or HD in the area. Is it a requirement? We didn't use it for the kitchen tile that was laid over 6 months ago and it is fine.

It does make one wonder why stores sell the SLC, but not the primer that the SLC says is needed first.

    Bookmark   April 12, 2011 at 6:48PM
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