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Unread 06-08-2016, 11:00 AM   #1
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cure time of modified thinset for exterior install over aquadefense with epoxy grout

Dear fellow pros, I'm a GC repairing a partial failure of an exterior terrace in New York with 8"x8"x1/2" quarry tile over ditra over 2" mud over a primary roofing membrane. I installed 600 sq feet on three terraqes in 2013 but the nonsanded grout was starting to wear away so I decided to remove it and install epoxy grout. Most of the job went smoothly until we got to the last portion of a 150sq ft terrace. After grinding out the grout we noticed 2/3rd of the tiles were loose and popped right off. The thinset didnt adhere to the back of the tile but was solidly embedded in the Ditra. I removed all of it including the 50ft of well secured tile over white thinset as opposed to the grey thinset that failed. I concluded my that back in 2013 my employee ran out of the unmodified thinset I purchased for the job and switched to a modified thinset that Ditra does not recommend. I ended up pulling off all the Ditra and used Mapei aquadefense instead. I then used a modified thinset as recommended by Mapei and reinstalled the tile. Now for my question. Ditra says no modified thinset, I assume do to cure times. Mapei and Hydroban reccommend modified thiset over their impervious membranes which I used but which contradicts Ditra's thinking. Now how long should I let the new modified thinset cure before I install my epoxy grout. I'm worried I will seal in any remaining moisture and the sytem will fail again. Thanks
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Unread 06-08-2016, 02:35 PM   #2
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Welcome Seth.

What were the installation conditions? Temp, humidity, exposed to weather, etc...

What modified mortar?

Same 8x8 quarry tile?
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Unread 06-08-2016, 04:02 PM   #3
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The current installation over the Aquadefense is with Mapei Ultraflex 2 installed in 75 degree weather at about 30% humidity. Mapei tech support told me I only need to wait 24 hours before using the epoxy grout but I have serious doubts about that. Schulter must have had numerous issues of modified thinset failure over Ditra before they starting specifying unmodified thinset. I still haven't figured out why Schulter still calls for unmodified thinset when other manufacturers like Laticrete and Mapei specify modified thinset over their liquid membranes which I assume have the same exact "breathability" issues as the Ditra. I'm using the same 8x8 quarry tiles
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Unread 06-08-2016, 05:17 PM   #4
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Mapei would know what their materials take to cure, but give it longer if you're uncomfortable. At your install conditions, a couple days should be plenty with maybe some added time for lower night time temps depending on how low they got. Their cure times are based on 73F & 50% RH.

Regarding why Schluter requires unmodified and every other membrane manufacturer requires modified, there's been some discussion on that around here. I'll see if i can find a thread or 2...
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Unread 06-08-2016, 05:28 PM   #5
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Thanks for the advice.
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Unread 06-08-2016, 08:08 PM   #6
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Hi Seth. I would be very comfortable with only the recommended 24 hours with any quality modified mortar intended for outdoor use, for that tile. Schluter's concerns/failures center more around large-format porcelain tile, not relatively smaller quarry tile.
I think it is very unlikely (near impossible) that merely switching to an unmodified caused your failure for 8x8 quarry tile that was otherwise installed the same as the area that didn't fail. More likely is a change in installation method, especially in regards to the amount of water in the mix and letting it skim over or be exposed to the sun for too long.
Modified generally has a higher bond strength, and so is much more forgiving of those types of errors that hired help make, whereas non-modified often must be installed almost perfectly. So it's more likely I think that the the non-modified, for that tile, actually could have slightly contributed more to the error because of it's low bond strength.
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Unread 06-09-2016, 04:34 AM   #7
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Actually the areas where we used white unmodified thinset were very secure. We had to chisel the tiles off. It was the area on the same terrace, installed the same day with the grey modified thinset that failed. Not really sure exactly what happened but my installer reminded me that we grouted the job within 1-2 days of completing the install. Out of a total of 600 sq ft only that small 100 sq ft area failed where he changed thinset. The weather conditions and sun exposure were the same for both the main areas that held and the small area that failed.
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Unread 06-09-2016, 08:49 AM   #8
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Which thinsets did you use?
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Unread 06-09-2016, 11:54 AM   #9
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Can't remember the exact Mapei products for that job, probably Kerabond for the unmodified and Ultraflex 2 or 3 for the modified
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Unread 06-09-2016, 04:47 PM   #10
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FWIW, between liquid and sheet waterproof membranes, you need to look at both their water proof (should be if installed properly) AND their vapor transmission. In many situations, a sheet membrane has a significantly lower perm rating. Ditra's perm rating is essentially zero at 0.006perm at least from below, probably 100x or more better than the best liquid membrane. IOW, moisture will not dry out through Ditra, requiring it to get out via the tile or grout.
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Unread 06-09-2016, 08:30 PM   #11
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Thanks Jim, definitely didnt know that. So all waterproofing membranes are not created equal. Aquadefense, Hydroban, Red guard etc allow for greater vapor transmission than the Ditra, correct? Do you think itrs safe to close up that quarry tile with the epoxy grout after 72 hours?
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Unread 06-09-2016, 10:05 PM   #12
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But vapor permeability would allow typical macro moisture to dry so slowly that any difference between the two types would not make a relevant difference in curing until far, far after both are good & plenty cured. It's irrelevant, which is a small part of why unmodified is not requirement of the other low-vapor-permeable membranes (Even Schluter Europe disagrees with the unmodified requirement for the very same Ditra membrane!).
It is fully safe to grout with epoxy after only 24 hours with 8x8 quarry tile and the mortars you mentioned.
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Unread 06-10-2016, 07:24 AM   #13
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Thanks Tom. Any idea then as to why that area failed? As I mentioned the thinset was well established into the Ditra but did not adhere to the tiles. The first fifty sq ft was stable as a rock with the unmodified thinset.
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Unread 06-10-2016, 09:37 AM   #14
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Schluter Europe requires one of the modifieds that will cure in the presence of excess moisture. I was told by Schluter in a class that the issue there is based on trying to get all EU countries to agree. That effort was just too onerous, even though they know the unmodified works just fine. Since the EU has area requirements for multiple countries, they did not want different instructions in one verses another. In the USA, they only had to deal with one approval agency for a very large market. This is why there are differences in installation requirements, not because what they specify here doesn't work, and work well IF you follow the instructions. FWIW, Schluter will warrant an install with a modified over Ditra IF you call them AND use a suitable one that will gain strength in the presence of excess moisture (typically, a rapid setting mortar, but not all of them). The problem comes when you use a latex-modified mortar...those typically need to dry to attain their strength in addition to the curing which happens regardless. One reason why Laticrete's StrataMat uses a modified is that it is not waterproof...it has holes in it intentionally, to allow moisture to escape.
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Unread 06-11-2016, 03:36 PM   #15
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Quote:
The current installation over the Aquadefense is with Mapei Ultraflex 2 installed in 75 degree weather at about 30% humidity. Mapei tech support told me I only need to wait 24 hours before using the epoxy grout but I have serious doubts about that.
Hard to believe Mapei's tech would recommend the Ultraflex 2 over Aquadefense for an exterior installation , in New York .

Quote:
I installed 600 sq feet on three terraqes in 2013 but the nonsanded grout was starting to wear away
Why did you install an unsanded grout for a floor application -- quarry tiles -- ?
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