Basement Tile - Moisture - Porcelain - Ditra Question - Tiling, ceramics, marble - DIY Chatroom Home Improvement Forum

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Old 04-15-2014, 09:51 PM   #1
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basement tile - moisture - porcelain - ditra question

Hi All

I have a basement in a house that was built in 1950s in Bergen County NJ. It's about 800 sq feet and has 9*9 VAT tiles. I am planning to remove them - scrape the mastic as much as possible and then install new tiles over it. (removal of old tiles and mastic scraping is being done by a contractor).

I read these forums for tiling and have gathered a few facts.
1. I should not try to 'trap the moisture in the basement floor - i.e. let the moisture come out - and for that ceramic tiles are best - otherwise the moisture can come out from the walls / mold.
2. I should use ditra - it's recommended as best.
3. Porcelain tiles are stronger then ceramic.

I gathered these three facts in different forums, and some-how the combination does not go together.

If Porcelain is better than ceramic, and I use Porcelain - am I inviting mold on walls - i.e. will the moisture be trapped under the Porcelain tiles and will it try to go out of the walls?

Same Question about the ditra - if that's supposed to keep the moisture away from the tile, where will that moisture go? will it try to get out of the walls?

Thanks in advance


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Old 04-15-2014, 11:48 PM   #2
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Do you have a moisture problem? If you do, deal with that first. Tile will neither solve nor make the problem worse.

That said, Ditra is an uncoupling membrane meaning it allows a small amount of movement in the substrate without affecting the tile/grout. Its kind of wasted on a good concrete floor in that aspect as concrete does not have the movement that a wood floor does. It can be used as a moisture barrier but requires a specific installation method with kerdi-band at the seams and up the walls a few inches. However that method is more for moisture proofing the substrate from moisture that comes from above ( IE an outdoor patio or a floor that gets washed down regularly). Again that method is wasted on a regular basement floor.

Porcelain is harder than ceramic and as a result, probably more dense so not as moisture permeable. But again, neither tile is a moisture barrier. People pick porcelain over ceramic because it is more durable and the color generally goes through the tile vs just the glaze on ceramic tiles.


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Old 04-16-2014, 10:33 AM   #3
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Agree with quagmire. Ditra does trap moisture above it, but not below it. This is because of the channels built into the bottom. This is why they recommend modified thinset on the bottom of Ditra, and unmodified thinset on top. Modified thinset must dry to reach full strength. Unmodified does not need to do so. If modified thinset were used on top, the only way for it to dry would be through the grout lines, which would take many months. Kerdi works the same as Ditra as far as trapping moisture above, but it's OK for unmodified thinset to remain wet.

You need to address the reason the moisture is there. Normally there is no need for Ditra over concrete, since you don't need to decouple the tile from the concrete. Concrete is dimensionally stable, unlike wood for example.

If you did use Ditra, any moisture trapped underneath it would dissipate through the channels toward the side walls. I think this would be unlikely to cause a mold issue, but I don't know. If it's a small amount of moisture and you didn't use Ditra, I don't really see any difference between your tile installation holding that moisture, and the concrete holding that moisture (for example, if you left the concrete floor bare.) In other words, if you have problems with a bare concrete floor, you'd have the same problems with a tiled floor. If there were not problems with a bare concrete floor, I don't see how tiling it could cause a problem.
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Old 04-16-2014, 09:17 PM   #4
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Anamika or Anamkia,

You first have to determine if you have a moisture problem as asked in #2 above. Tell us more about the history of the house in regards to moisture including what your nose tells you.

If you have hydrostatic pressure, nothing will work, including ceramic tiles. BTW, porcelain tiles are ceramic.

There is no contraindication with the 3 concerns you listed. But lets see what you answer.

I understand you have 9x9 tiles now. Do you know whether they are vat or asphalt, are you sure? How thick are they and do you know when they were installed? Is there a musty smell, how about after removing a few? Ever have standing water? Are some tiles loose, kept in place by gravity? When will the removal start? Got pics?

TILE GUY - retired- TROY, MI - Method & Product suitability consulting.


Last edited by JazMan; 04-16-2014 at 09:19 PM.
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