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Old 12-27-2017, 12:27 PM   #1
ia_alex
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Ditra Heat Floor - No Bond!

Hello,
My first post here, what a great resource for tile!

We have a situation at our new home that was built late in 2016. Our bathroom floor which has Ditra Heat and 12x24 tiles have began to crack out the grout lines and some have a bit of a 'crunch' sound to them. We have quite a bit of tile in our house and this bathroom is the only floor where we're having this issue (as of now).

This morning to investigate, I pulled off some trim and cut out the grout along a few of the loose tiles making sure to only dig down 1/4" to avoid hitting the cables. The pictures below are what I found. It seems that being the tiles popped off very cleanly with little effort with the claw of a hammer that there was hardly any bond other than the grout holding them together. I do know the installer followed the Ditra installation book to the T (using modified for laying ditra, non modified for setting, and we waited a full month before starting the heat), but not sure what could've caused the non-bond other than from what I read; skimmed over thinset and/or not back buttering the tile.

I was very involved in the construction of the house having had a few homes built previously. The floor specs are 16" open web trusses 19.2" OC with 3/4" T&G OSB.

I am aware that this is nothing short of a tear out and replace situation. What my question is, is if I can be assured that the Ditra is bonded to the floor and we can get the tile removed cleanly without damaging the cable, is it possible to do a skim coat over the thinset and relay without having to pull up and redo the Ditra and cable? Understand that the floor height will be slightly higher, but have heard horror stories of having the remove Ditra. What may affect that decision is that when I pulled up the tile, I noticed the thinset was cracked in a few places, it looked mainly to be right where the cables are for the most part. Is that something that I should be concerned about?

Thank you everyone in advance for your help!
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Old 12-27-2017, 05:20 PM   #2
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Pics show that the tiles werent properly set and never had sufficient coverage. Trowel ridges weren't collapsed and looks like no burning of thinset on the back of the tile. It looks like the thinset had started to skim over as well like you mentioned. If the tile had a thick layer of kiln release on it that could have contributed to the kick of bond.
As far as reusing what you have...that would be a question to ask schluter. I would be afraid of compromising the ditra to subfloor bond when prying on the tile.
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Old 12-27-2017, 06:09 PM   #3
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It's a tough situation to be in but there's no way we can know the answers to your questions. At this point all you can do is continue to remove tiles and hope they all come up as easily as the first few. Like Ryan said, damaging the wire is a concern along with the bond between the Ditra Mat and OSB. The crunchy tiles will probably come right up and I would guess those are in the traffic areas.
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Old 12-27-2017, 09:08 PM   #4
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So I continued on this evening. The get-it-done-right mind in me ended up taking out more tile, and a couple sheets of the Ditra. I've decided that its probably best to start from scratch with new Ditra and cable.

My findings tonight:

- All tile is still coming up easily. I am taking a grout saw and taking out the grout before prying out the tile. You could hear what little bond there was with the tile continuing to pop as the grout was being taken out. So far only one tile broken. Even the ones with almost full coverage seem to be coming out just as easy.

- I pulled up a few sheets of Ditra with the intention on replacing it and the cable. Using a 5 way painters tool to scrape it up. It seems to be bonded pretty well, however the thinset is mostly bonded to the OSB yet, fleece still on the Ditra. Some pieces even took up a few flakes of OSB. Fair to say Ditra fairly bonded well?

- Noticed a seam in the OSB where the thinset cracked through. You will see in the pictures there's a decent gap in the one area, but I believe it's recommended by Advantech to leave an 1/8" space or so between sheets on the ends.

- Setting thinset is cracked where cables are ran.

Questions,

- Attaching a picture of a row of tile along the base of our vanity. I'm hoping to leave the last row of tile there. Cut the ditra along that line and start new from there out. The vanity is wall to wall and I don't see it being an easy task getting it out. Also will never know if the tile under is loose or not.

- Recommendations on the best thinset materials to be using from applying the Ditra to setting the tile (this time back buttered!)? Want to make sure I'm not scraping by and I get the best floor with no worries.

Please see attached pictures and let me know if there's anything else I should be assessing!
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Old 12-27-2017, 10:05 PM   #5
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1. Nope, if the ditra was installed properly the fleece would still be stuck to the floor and I would be able to hear you cussing all the way at my house. It looks like that contributed to the failure. The thinset needs to be wet enough to flow around the fleece and yours looks like it was too dry possibly.

2. 1/8" on butt joints is good, properly fastened is important.

3. If you want to leave it, its up to you. Probably wont make any difference unless that row begins to pop.

4. You'll get varying opinions on thinset because everyone has their own favorites.
To set the ditra: Laticrete 254 platinum
As for the tile...I use modified thinset. If it were me I'd go with: Ardex x5, Ardex x77, Laticrete tri lite, laticrete 4xlt, or any one of their medium bed thinsets.
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Old 12-28-2017, 04:44 PM   #6
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ONce properly embedded in thinset, the fleece becomes essentially one with the mortar...they don't part easily! Every try to get hot wax out of fabric...not easy, and mortar doesn't melt like wax does!

It may be that the installer just spread too much thinset before he tried to cover it with both the tile and first the Ditra. You really do want to burn a layer of thinset into the back of any tile, but it is much more critical trying to set a larger format one. Plus, the thinset on the substrate does still need to be fluid. While you can push and shove a small tile fairly well to embed it in thinset, your weight spread out over a large format tile is really quite small, and they don't move easily once you lay them down, so having the thinset the proper consistency and having some already embedded into the pores on the back of the tile go a very long way towards making a solid bond.

It doesn't hurt to take a damp sponge and scrub the back of the tile before you try to set it in place...you don't want it dripping, but damp will wash any mold release and dust off, making it easier to get a good coat of thinset to stick. If it is tried while still wet, it will be problematic, slightly damp shouldn't be an issue.
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Old 12-28-2017, 06:40 PM   #7
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Do any of the joints in the subfloor line up with cracks in the mortar, whether above or below the membrane?

Dampening the subfloor immediately before spreading mortar and mixing the mortar a bit wetter will promote a better bond between Ditra and subfloor.

Skimming the back of each tile with mortar will help them bond to the mortar spread on the floor. Proper notch size, and spreading the proper amount to prevent skinning is also important.
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Old 12-28-2017, 10:09 PM   #8
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Thanks everyone for the input. An update on tonight:

- Finished pulling up all tile. No broken pieces as they all came up fairly easily after sawing out the grout. I did notice the few tiles that were fully embedded (but not backbuttered) did take a little bit more prying, but still came up in one piece. No thinset to speak of on the back of any of the tiles. It all stayed on the Ditra.

- Started pulling up Ditra, again came up fairly easily. I did take a scraper and it seems that the subfloor thinset will scrape off on most of it. Would it be beneficial to take a rubbing brick to smooth out what's left?

- Last question for the night: I'm thinking about burning in a thin layer of thinset on the subfloor, letting it sit overnight and starting on the Ditra the next day. Would this be of any benefit bond wise?
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Old 12-28-2017, 11:04 PM   #9
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1. Yes, a rub brick, belt sander, or grinder with a diamond cup would clean up the floor. You can deal with a residue but I wouldnt leave any lumps of thinset. Use a respirator and a shop vac if you use mechanical means when removing the thinset.
2. I wouldn't. After you're done removing the old thinset, vacuum the area then sponge it clean changing out the water a few times. To get the best results use a damp aponge over the floor, spread the thinset using the correct trowel, mix the thinset using the highest allowable water content for your particular material, and make sure to embed the ditra into the mortar by going over it with a 2x4, grout float, or roller. Peel back an edge and make sure that you are getting 100% coverage.
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Old 12-29-2017, 02:16 AM   #10
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I have had very good adhesion by back buttering the felt side of the ditra when i put it down. It's easily done with the sheets of ditra.

How good of shape is that cable? Looks like it's coming up in tact.

Travis, that is a very good idea!
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Old 12-29-2017, 11:47 AM   #11
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With sawing out the grout, I'm not sure if I trust reusing it.

Buttering the Ditra is a great idea, will definitely do that.
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Old 12-29-2017, 11:55 AM   #12
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I've had my share of trouble getting a good bond with Ditra Heat underlayment to the subfloor. If you can get the sheets vs the roll it would help. Spending a bit more on adhesive for the underlayment to subfloor is a good idea IMO
The memory on the Ditra Heat underlayment is a real pita. Takes some extra care to make sure it doesn't lift and break the bond.

I had good luck with Ardex X78. I've had the best results with Laticrete 254. Ardex also makes a "glue" adhesive for underlayment. Ardex AF207, I've used it a few times with good results. there's info on the Ardex website.
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Old 12-29-2017, 01:03 PM   #13
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Schluter makes a tester for the heat cable so you can check it before you lay your new floor down. It’s highly suggested to test the NEW cables before you install the tile. A few phone calls and i bet you can find a tester to borrow or get someone to test it for you.

I think you are on the correct path by NOT using the old cable. To much work to risk it.
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Old 12-29-2017, 09:42 PM   #14
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As to the cable, if the megometer says it's good, and you don't see any nicks or cuts, it should be okay to reuse. This assumes you have the original values to know if it has changed. That test tool verifies that the insulation and conductor are in good shape. You can't rely on a simple ohmmeter to verify the cable is in good shape.
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Old 12-29-2017, 09:53 PM   #15
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Quote:
Originally Posted by jadnashua
As to the cable, if the megometer says it's good, and you don't see any nicks or cuts, it should be okay to reuse. This assumes you have the original values to know if it has changed. That test tool verifies that the insulation and conductor are in good shape. You can't rely on a simple ohmmeter to verify the cable is in good shape.
Yes, yes, yes!

Alex, you're getting a lot of good advice on this thread in general from lots of folks. I just wanted to drive Jim's advice home if you do decide to pursue re-using the cable. Pay attention to this post. A simple ohmmeter is NOT the tool to verify that the cable is in good shape.

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