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Unread 07-27-2008, 12:45 PM   #1
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Tile floor tenting

We live in coastal southern California. We had 12”x12” ceramic tile installed for the entire downstairs floor 10 years ago. The longest span of the floor is 45’. No soft joints were used. All visible edges were grouted, only the areas covered under the baseboards might not be fully grouted. Approximately 80’ of 18” wide strips of Composeal crack isolation membrane were used over the shrinkage cracks in concrete slabs.

A row of tiles between the living and dinning rooms tented 2" last winter. After thorough investigation, we found all tiles above Composeal have lost bound, some began to tent. The areas underneath Composeal along the hairline cracks show more moisture and some have mold. One strip of Composeal was installed in anticipation of future cracks. Without cracks and moisture, the strip still lost bound. For the 2” tented area, the Tramex reading is 6% underneath Composeal and is 4% without Composeal. At another slightly tented area between the family room and the kitchen, the Tramex reading is well above 6% under Composeal and slightly above 6% without. The house is surrounded by pavements; drainage is good and there are no plumbing problems.

The tilemen think the tenting is due to moisture vapor that pushed up the membrane and caused the tenting. But I think lack of the expansion joints and perimeter joints is the real cause of tenting and the membrane is just the weak point.

We have bought extra spare tiles, but not enough to replace all problem areas. Redoing the entire floor is too costly so we are seeking a solution to fix the problems.

Could someone help us with the following questions?

1. What’s the cause of the tenting?
2. How do we keep the tenting from spreading?
3. Since we don’t have enough tiles to replace all, can we just replace the ones that have tented and add soft joints to the edges of the loose but not yet tented tiles?
4. If we only remove the tiles that are tenting, will the remaining cut-up crack isolation membrane still be any good? What kind of crack isolation membrane should we put under the new replacement tiles?
5. Should we seal the crackline with caulk before installing the crack isolation membrane?
6. Is there any crack isolation membrane that's breathable so moisture will not be trapped underneath?
7. We may have problems to remove the perimeter grout without damaging the cabinets or walls. Are there any alternative ways?
8. Any suggestions for grout removing method that creates the least dust?

Your help is deeply appreciated!!!
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Unread 07-27-2008, 02:49 PM   #2
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Welcome, LPI. Please give us a first name to use or enter those initials in a permanent signature line if that's what you prefer to be called.

1. Lack of movement accommodation.

2. You already have. The tenting created a very fine movement joint in those places. If the tented areas leave you with tile fields no larger than 20 feet in any direction (assuming this is indoors and without substantial direct sunshine), you are within spec for movement joint placement.

3. You should be able to do that, so long as that also allows you to honor the control joints in the slab.

4. Not likely. I would contact our friends at the Noble Company. They have some very effective crack isolation systems that might work for you, but I hesitate to tell you how much tile to remove and how to install the membrane. I think you'll want to do it right this time. Sounds like you used about half the recommended width last time. But using wider crack isolation membrane still won't help if you don't also include the recommended soft joints in the tile surface.

5. I wouldn't bother.

6. Not really, but I don't think you care. If your moisture readings are accurate, I doubt you have a moisture problem at all. But I question just what you are reading with that Tramex meter. I would not trust mine to actually tell me the moisture content of a slab on grade. It will, however, give me a very accurate gauge of the difference between one area and another. If you really want to know if you have a moisture vapor problem, get a couple of inexpensive calcium chloride test kits and install them for a few days.

But, again, it doesn't sound to me like you have a serious moisture problem. And even if you do, your tenting was still a result of a lack of movement accommodation.

7. Not to my knowledge.

8. Use lots of water with whatever tool you employ.

My opinion; worth price charged.

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Unread 07-28-2008, 02:22 PM   #3
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Question Floor tile tenting

Thank you very much, CX.

Most membrane sheets have a width requirement. It may not work if we want to replace only the tented tiles. Is there any crack isolation product in liquid form that we can apply prior to thinset?

I think Composeal blocked the moisture from evaporating so we have mold problem. Is this a common problem? Are there any breathable products out there?

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Unread 07-29-2008, 04:44 AM   #4
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We have bought extra spare tiles, but not enough to replace all problem areas. Redoing the entire floor is too costly so we are seeking a solution to fix the problems.
I'm thinking that this would be a god opportunity to put in some sort of pattern mixing existing tile with new colors.

Denise Gunnels, Realtor

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