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Unread 11-15-2004, 08:31 PM   #1
D Tom
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Exposed aggregate concrete, Ditra, porcelain tile

I'm new to this board and have spent the last few days lurking and learning ALOT!!! Getting ready to tile a outside covered area with 16" x 16" porcelain tiles. (See attached pixs) I'm in Southern Indiana and temps are in the 50's during days and 35-40 at night. (1.) Any considerations I need to take into account for temperature?

Part of the area is exposed aggregrete concrete. We extended it a few months ago with regular concrete. The aggregate part was sealed a few years ago, but I think for the most part worn away by the sun (before I added the roof.) I just completed a weak (1 pint/gal) Muratic Acid wash on the whole area to prep. (2.) Is there any other prep I should be doing?

Planning on using Ditra. The discussions on non-modified versus modified is making my head spin. I have printed out the latest handbook from Schulter and noted the recommendation of non-modified below and above the Ditra. I concerned about bonding issues though with porcelain and non-modified. (3.) Sounds like I want to use a "loose" or "wet" mix of non-modified to aid in that? Any other thoughts on thin-set type for this specific job?

(4.) Do I need to apply much pressure when laying down the Ditra and what's the best way?

(5.) Are there any other specific "you better what out for's" from anyone before I start this?

Thank you in advance for any help you can give to above. My biggest fear is a bunch of loose tiles a few (or more) years from now!


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Unread 11-15-2004, 09:02 PM   #2
Bill Vincent
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Tom, I would give serious consideration to holding this project off till after the spring thaw. It's too cold at night now, and that'll come back to haunt you if you try it now.
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Unread 11-15-2004, 09:29 PM   #3
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What Bill said.

For purposes of curing concrete in thicker sections (foundation slabs, etc), which benefit from the heat of hydration, the weather is considerd "cold" if it's averaging below 40F degrees for several days and the daily temprature is below 50F for more than half of a 24 hour period - or something like that.

With the very thin sections used in setting tile, the whole of it will be cold within an hour or so and the necessary hydration will be very, very slow. If you're using thinset with latex or other additives, there are probably other problems as well, but I'm not familiar with them.

That's not to say you can't do the job now, but If you can't stay off the set tiles for at least two weeks using an unmodified thinset (not sure that's recommended outside), I would wait for warmer weather. The thinset may well cure out as strong as in 72F degree weather (28 day cure), but it will have very little strength for the first week or probably two.

All that, again, is from experience with thicker Portland cement pours, but I'd expect the problems to be even more pronounced in something as thin as a tile thinset layer.

My opinion; worth price charged.
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Unread 11-16-2004, 06:02 AM   #4
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Thanks for the responses on the temperature question. That got me thinking. This area is such that I can seal it in with plastic sheeting. Could run a propane heater in there for a couple weeks afterward. I do have the luxury of being able to keep off of it while it cures. What do you think?

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Unread 11-16-2004, 08:53 AM   #5
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That'd be fine, Tom. Then you wouldn't be doing an outside job at all. I'd want a small heater out there for a couple days before you start working to warm up the slab a bit. Then you just wanna try to keep everything above 55F if you can for a while. Two weeks should be plenty after you grout. One week would probably do it (the thinset's gonna dry before it really cures anyway), but two would be better. Hell, leave the sheeting up until Spring so's you can use the new patio.

My opinion; worth price charged.
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Unread 11-17-2004, 09:52 PM   #6
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I've got my plastic tent erected around my complete patio and enclosed. Set up to heat with a propane heater.

I've set a few 12" x 12" test pieces of Ditra yesterday using un-modifed thinset and I'm suprised at how long it is taking it to set. After 24 hrs, I could easily pull the mat up and the thinset seemed the same consistency that I put down the night before!! (I did use way to much...used a 1/4 x 3/8 trowel...bought a 1/4" x 3/16" V-notch tonight.) Slab temp was around 55F. Around the edges of the Ditra it was setting up, but slow.

Have any of you ever laid over exposed aggragate? How have you prepped it? The sealer on this is old and seems to be about gone, but I'm wondering if there is enough left that it is not letting the moisture get out.

Something just doesn't seem right.
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Unread 11-17-2004, 10:45 PM   #7
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Thinset, being a cemetaceous (sp?) product chemically changes by bonding water into the structure. Cement will actually set under water (if it doesn't get dispursed) into a solid mass (or hard grains if it does). Some of the modified stuff needs not only to chemically change but also to dry. The Ditra does not allow moisture to escape through it. That is why the selection of thinset is important. If your slab beads water, any moisture from the thinset can only escape through the edges, and will be significantly slowed by cooler temperatures as well as the impervious layers. In addition, to get the Ditra to bond well with the thinset, it really needs to be on the wetter side and this could slow the setting as well, so, not sure what to tell you. One of the pros will probably pass on their thoughts...
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Unread 11-17-2004, 11:21 PM   #8
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Ditra What?

My interpretation of the literature that precedes Ditra is-
A dry set morar that is not modified by latex(Dry or Emulsion) is better suited for exterior installations that are subject to possible rain periods durring the time directly following installation. I believe this is mainly because cement, on it's own, (when mixed with water) cures with a chemical reaction regardless of the ammount of water introduced durring the curing proccess. On the other hand, the latex that is added to modified mortars can be re-activated durring the curing proccess when excess water is introduced, resulting in a weaker or softer final set.

I'm sure one of the pros will fine tune this statement, or correct any misconceptions that I may have.
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Unread 11-18-2004, 05:51 AM   #9
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What your doing is still pretty risky with the Tent.Let me explain.
Bricklayers can get away with this because they are not dealing with transferring ground temperatures.Being an Outside slab its not likely it had insulation installed below it.Heating the area and getting that slab up there to a consistant 60-65 degrees is going to help.it will take awhile.
As a pro, i wouldnt take a job like this on because it just wouldnt be cost effective for the homeowner.You can do this if you pay attention and get that slab so that its maintaining heat above 60 degrees.If it falls down to 55 you may lose enough heat through ground transfer to affect your bond.it will definitly affect your cure time especially with Ditra.
I'm of course up north where temperature swings can be extreme.watch your weather crank up the heat and keep your eye on that slab temp!!!
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Unread 11-18-2004, 11:18 AM   #10
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Thanks Guys. I'm thinking what is going on is a combination of temperature and left over sealer on the concrete.

I think I can deal with the temperature.

I think I'm going to rent a concrete floor surface grinder this evening and try get the concrete more 'receptive' to absorbing water.
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Unread 11-18-2004, 05:34 PM   #11
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Hoosiers.

Can't wait till summer, huh?

A good quality dry set mortar such as Customs Master Blend will do the trick. And you are correct in that it should be kept "loose" and not too stiff.

You do need to push the Ditra into the thin set immediately. I use a block of 2x4 usually -- about a foot long. You can get both hands on it and lean on it as you push it around over the surface of the Ditra. I can't apply quite a bit of pressure this way with my 220 lbs of body weight.

In you neck of the woods I think I would go ahead and waterproof the installation by taping the Ditra with Kerdi-band or with cut strips of Kerdi. Might even flash it up the walls a little. If you can keep water from getting under the installation in winter, you'll be fine.

Had to come back to explain why they don't want you using modified thin sets in areas where they can get wet not long after installation. There are apparently certain modified products that can loosen up if wetted before they have a chance to completely cure. Dry set, on the other hand, cures entirely by hydration, just like concrete. Wetting it actually contributes to its strength.
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Unread 11-18-2004, 05:40 PM   #12
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i would call the mfg. involved and get their blessings ! dont want to find out next spring you are on your own..get it in writing.
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Unread 11-18-2004, 06:21 PM   #13
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What did I miss, Eric? Clue me, will ya?
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Unread 11-18-2004, 07:43 PM   #14
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I talked to Eric offline. He's concerned about the temperatures and the need to use heaters, etc. I agree with him (and with Todd). You should wait until late spring/early summer.

He has also reminded me that Custom Building Products had never agreed with Schluter as to the use of un-modified thin set. For this reason I agree with Eric that you should call Schluter and get them to sign off on your installation if they will. Otherwise, you'll have no warranty from anyone on this job.
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Unread 11-18-2004, 08:03 PM   #15
D Tom
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Thank you for all the input guys.

I am seriously considering delaying this project until spring. This is alot of cost in materials if something goes wrong.

I do think I need to deal with the sealer on the exposed agg though, no matter when I do it. I stopped by a rental place today and looked at some tools. A couple of options....

One is a walkbehind surface grinder that has a 11" diamond disc. Designed to run wet.

Another is a walkbehind scarifier with a variable depth setting.

Both look like they would do the job. The surface grinder would leave probably a smooth (maybe too smooth) surface when done. The scarifier would leave a rough surface. Maybe a little rougher than the current exposed agg

I also got to looking and thinking...why shouldn't I use something like Redguard instead of Ditra?
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