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I am tiling a basement bathroom that is 5 feet by 6 feet. It has a crack running the entire length of the bathroom as well as a small hairline crack near the toilet. I've read that Ditra is the best for crack isolation and to keep the movement from transfering up through the tile.

I am using 1 foot by 2 foot tiles running lenthwise over the crack. My problem is if I use Ditra with the thinset underneath it + the Ditra it self and the thinset on top I'm way too high to match up with my wood floor that is meeting up with it.

I've seen a few other online putting crack isolation membrane over the floor, but it sounds like that is more for prevention, not for cracks that are already in the floor.

Are there any other low profile options to prevent the crack from traveling up into the tile or grout?

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    What kind of tiles are they? – Joe Phillips Jul 5 '15 at 17:50
  • They are porcelain – TreK Jul 5 '15 at 19:47
  • I also failed to mention that the floor is about 7 years old. I'm not sure how much the floor will continue to move over the year? – TreK Jul 6 '15 at 4:41
  • Is there a membrane under the wood floor? – DA01 Feb 1 '16 at 21:52
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Use a thinner crack isolation sheet, ask for "slip-sheet" at the tile store. Some will bridge cracks up to 1/8" wide. Note, although slip-sheet works great for cracks caused by horizontal movement, they are not great for preventing cracks caused by vertical movement.

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Ditra is excellent, why not use a transition strip from the tile to the hardwood. You can get them in marble, stone or metal and they are perfect for situations like this. You don't want to be tearing up the cracked tiles in 1 year.

  • That is the decision I am struggling between. I don't want to be tearing up tile in a year. But I would really like to avoid the uneven transition strip. – TreK Jul 6 '15 at 4:40
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The crack in the basement floor looks like it goes under the wood as well. Cracks in foundations tend to let water in. Water + wood = mold. I hope you have sufficient crack repairs done and an underlay in place that will help to prevent moisture transfer into the wood floor, but most options I am aware of would make the wood floor match up closer in height to a tile floor with Ditra in place.

If you haven't secured all of the wood flooring yet, I would strongly recommend fixing the crack and the cause of the crack if you haven't already and then look at subfloor underlays for the wood flooring to help with moisture control. This will allow you to use Ditra and have the tile floor match up with the wood floor. This will hopefully keep you from having to tear up cracked tile and a moldy wood floor after only a few years.

Also, If the wood planks haven't been secured yet and there is a possibility of returning them, I recommend thinking about switching to an inorganic flooring material (e.g. vinyl plank flooring looks nice and is great for basements). I recommend switching materials if at all possible or holding off if the cause of the cracking is unknown or more cracking in the floor/walls can be expected (e.g. if the current cracks were caused by house settling). In general, the use of wood flooring in basements is not recommended unless the basement is bone-dry and can be guaranteed to be bone-dry in the future.

  • Thanks for the comments. I have taken every precaution and spent a lot of money on "special glue" that provides a moisture barrier for the wood. Additionally, I live in a very dry climate so I'm hoping that all stays mold and moisture free for many years to come. – TreK Jul 6 '15 at 21:44
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If you don't want to change the height of the floor with a traditional rubber membrane, you can use a waterproofing/isolation membrane called RedGard. It is applied like paint, and only would add a fraction of an inch to the height of your floor.

The manufacturer recommends that you put on one coat to act as a crack isolation membrane, and 2 coats to be waterproof. Since this is an on grade slab, it wouldn't hurt to add a second coat to prevent water from being absorbed from the ground under your tiles.

A crack that size will surely telegraph into the tile. Before you apply the membrane, you should fill the crack with hydraulic cement or mortar. After the crack is filled, you can use your level to find any high spots, and then grind them flat with a grinder that is equipped with a diamond cup wheel.

Since this is in the basement, it would also be a good idea to use a mold resistant grout. This will keep the floor looking new for a long time.

Those tiles are going to be ice cold in the winter, and I also don't see any other heat source in your picture. One other thing you could look into is an under tile heating system. They can be a little on the expensive side, but would be perfect for your bathroom. Some of them also act as an isolation membrane too, so there will be less of a chance of your tiles cracking.

One last thing to consider is installing a stone threshold. Even if you don't change the height of the floor, you can get one that is the same thickness as your wood floor and the tile. It will give you a much cleaner transition from the tile to the wood. There are also a wide variety of thresholds available on the market which are designed to overcome height differences. If you are concerned about tripping over it, there are ones that are beveled. You shouldn't have a problem finding one that works for your bathroom.

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