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Unread 02-16-2020, 08:41 PM   #1
SL_gold
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Ditra, Cement Board and Grout questions for Laundry Room

A friend is helping us tile our laundry room and we had a few questions based on some things he said. The room is over a basement and the joists are 16" OC and 9" width. We had tile for years in the adjoining room with no issues so he thinks the deflection is okay. The tiles are large format 12x24.

1. He suggested that we could use Ditra rather than cement board. Is there a reason we should use cement board instead or is Ditra a good way to go?

2. Ditra requires unmodified thinset, but the thinset for large format tile recommended at Home Depot is modified. He stated we should still use the unmodified...what do you think?

3. We had purchased pre-mixed grout and he was adamantly against that and said we should use cement-based grout that we have to mix. Is pre-mix really not the way to go? He did say that there is always the risk of efflorescence on the grout with cement-based but shouldn't be an issue.

4. Any other advice that you can offer?

Thank you.
Steve and Linda
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Unread 02-16-2020, 09:23 PM   #2
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Welcome. Since we know Steve would never read the directions or ask for direction, I'll call you Linda.
Quote:
Originally Posted by Linda
The room is over a basement and the joists are 16" OC and 9" width.
I'm guessing you're telling us you have 2x10 joists, but you've not told us the species, condition, or unsupported span thereof. You can use the Deflectometer in the dark blue bar near the top of the page to get an initial go/no-go reading.

And we need to know what you have for a subfloor.

1. The choice between using a CBU or an uncoupling membrane is up to the installer. Some of the choice might be governed by the subflooring or the adjacent flooring, but either of those substrates, properly installed, is acceptable for your tile installation.

2. Thinset is a method, thinset mortar is a product used for the installation of ceramic tile in the thinset method. I'll guess that you have a plywood subfloor, or will have one, so the choice of mortar for the application of Ditra would be a modified mortar meeting the standards of ANSI A118.11. No exceptions there, for Schluter or anyone else. Bonding to plywood, use a modified mortar meeting A118.11. For bonding the tiles to the Ditra you get a choice of whose requirement you wanna honor. Schluter wants an unmodified mortar (A118.1) and that will bond to the tile if done properly. The tile manufacturer will want a modified mortar (A118.4 or better) and many of those will work just fine over the Ditra, but you'll not get a warranty from Schluter. You don't need the warranty because any failure you have will be an installer error. Up to you. The modified mortars in general are a bit easier to work with than the unmodified mortars, but there are some unmodified mortars out there that are easy to work with, too.

3. The Flexcolor CQ should be fine for your grout. It's a bit different to work with than the cementitious grout your friend is recommending, but if you've not worked with either you won't know the difference. You just read and follow the manufacturer's instructions carefully and you'll have no problems.

4. Tell us more about your floor structure.

My opinion; worth price charged.
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Unread 02-17-2020, 05:09 AM   #3
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Thank you CX. I'll measure the spans and let you know what I can find out about the type of wood. I do know there is some writing on it that is dominated by a "2".

Back to the grout...is there a benefit of using the powder over the pre-mix. What would you use in your home?

There is also a portion of the floor you can see in the pic that looks like it has a sheet of underlayment over the plywood. Not sure why only in that area. Is this an issue for the modified thinset mortar as it states no to use it over Luan. I can't tell what thickness it is but it has a lot of staples in it. Linoleum was in the room.

From the TDS: Do not bond directly to hardwood, Luan plywood, particle board, parquet, cushion or sponge-back vinyl flooring, metal, fiberglass,
plastic or OSB panels

Thank you.
Steve
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Unread 02-17-2020, 08:11 AM   #4
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Welcome, Linda and Steve,

You can do a search on "Flexcolor CQ" here and come up with many threads/posts, delivering to you many hours of reading, after which you can make an informed decision. I believe the threat of efflorescence is reserved for tiling over a concrete substrate.

Yes, the Lauan - if that's what you've got over the plywood, must be removed.

What thickness is the plywood?

As for the modified vs. unmodified over Ditra debate that, too, as been discussed in detail within these pages. IMO, it is key to understand that no thinset mortar actually bonds to the top of Ditra, it is mechanically held in place by the shape of the waffles.
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Unread 02-17-2020, 01:18 PM   #5
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Added pic of the joists. They are 2x10 (9" true) and look like #2 Hem Fir.
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Unread 02-17-2020, 01:23 PM   #6
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We're still lacking the unsupported span of your joists and the type and thickness of your subflooring, Linda. Both very important to your project.
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Unread 02-17-2020, 01:26 PM   #7
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You can use a modified over Ditra and uphold the Schluter warranty, but it must be Schluter All Set Thinset Mortar. All Set is also approved for your larger format tiles per Schluter.
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Unread 02-22-2020, 06:07 AM   #8
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Span

Hi CX,

The span of the joists is 12’ and the are 2x10s but true 9”. Plywood is just shy of 3/4”. Probably 11/16”...hard to be exact where I measured at the vent.

And I pulled up all of the Luan. Without exaggerating, there were 427 million staples that had to be pulled.

Thanks again for all your help.
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Unread 02-22-2020, 10:56 AM   #9
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While your estimate of the number of staples in the Lauan may be a little conservative, we'll accept it.

Sounds like your subfloor construction as described is adequate for a ceramic tile installation. The common depth of a nominal 2x10 joist is 9 1/4" by the way.

My opinion; worth price charged.
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Unread 02-23-2020, 07:42 PM   #10
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Okay...next set of questions. Probably not the last though...

1. For the Ditra, I know what size trowel to use. For the 12x24 porcelain tile on top of the Ditra...what size trowel is recommended. I will be using the VersaBond LFT from Home Depot.

2. For 12x24 porcelain tile, is there a recommended grout joint size?

Thank you very much.
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Unread 02-23-2020, 08:46 PM   #11
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1. You'll find a 1/2" square notched trowel recommended often for that size tile installation. If your floor is flat and your tiles are flat, you shouldn't need a notch that big, but, again, that's what you'll likely find recommended.

What you really want is a trowel that provides a minimum of 3/32nds of an inch of mortar covering a minimum of 80 percent of the back of each tile with good coverage under all edges and corners. Optimally you'd want that with a minimum squeeze-out of mortar into the grout joints. The squeeze-out is desirable, the coverage is mandatory.

Best way to determine what you need is to start with whatever trowel you choose, using your tile and your mortar and your technique and see how it goes with the first couple tiles. Lift them after they're set and see if you've got the coverage you need. If not, adjust either your trowel or your technique until you get the required coverage.

2. The ceramic tile industry recommends your joint width be at least three time the difference in size between your largest and smallest tiles in your layout. The manufacturer might have a recommendation. If so, follow that. If not, stand eight or ten tiles from different boxes together on edge and put a straight edge across the top and see what size difference you have. Multiply that by three and make your joints at least that wide.

My opinion; worth price charged.
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