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Old 10-30-2008, 02:09 PM   #1
devo
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Making up for different thicknesses of tile in floor application

Hello! We are about to begin a tiling project in our bathroom - first the floor, then the countertop - and we've been reading your forums for advice on subflooring needed and all that jazz. One issue we have that I haven't found in others' questions is the following.

We have two kinds of tile, 8x8 pieces of slate that are relatively uniform in thickness, and then small pieces of recycled tumbled glass that we are going to use to make a river pattern through our slate bathroom floor. The glass pieces vary somewhat in their thickness, but are mostly about half as thick as the slate, so we need to do something to raise them up a bit.

Our current plan is to lay the slate with thinset, leaving a space for the glass river, but thinsetting that river area as well. After the thinset dries, we'll put down another layer of thinset in the river area to set the glass tiles. Does anyone see problems with this plan and if so, what would you do instead to make up the tile thickness difference?

Another wrinkle in what we're doing is that under the tiles, we're also putting in an electric heating system by Warmly Yours, so that's yet another layer of thinset in the floor...
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Old 10-30-2008, 02:15 PM   #2
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Welcome to the forum, Devo.

What specifically is the difference in thickness of the tiles - 1/4"? 1/8"?

Your thinset idea can work so long as you're not putting down more than 1/4" at a time. It might be tricky to get it uniform though. I suppose 1/4" cement board would be too much. What about Ditra?
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Old 10-30-2008, 02:26 PM   #3
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Hi Devo,

You can make some sort of trick stick that will ride the thicker tiles on either side but that will have a lower straight edge in the middle for keeping your floated thin set consistent.
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Old 10-30-2008, 03:29 PM   #4
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Thanks for the responses!

I just went and measured both kinds of tiles more carefully. The slate ones are pretty consistent at 1/4" thickness. The glass ranges from 1/16" up to 1/4" - which means that some of the glass pieces are actually the same thickness as the slate (but most are more like 1/8").

So now we're thinking that we should try to lay them all at the same time (because otherwise the thicker glass pieces will stick up), but just have a somewhat thicker layer of the thinset in the river area to support the variation in the glass tile thickness...
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Old 10-30-2008, 05:22 PM   #5
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Just put a little thinset on the backs of the glass tiles and set as you go.
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Old 11-10-2008, 06:19 PM   #6
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thinset to use between OSB and hardibacker?

We've been reading the forum and talking to local professionals and reading the backs of bags of thinset, and can't figure out a single plan!

We have built a new OSB subfloor (2 layers, 23/32" thick) for our bathroom and are planning to put Hardibacker on it and then lay slate tile (we're OK on the deflection). I now realize that it would have been easier to figure this out if we had used plywood, but that is now not an easy option.

SO, on the forum, everyone says you really must put unmodified thinset under the CBU. Our problem is that thinset manufacturers all seem to specify NOT to use them on OSB. Hardibacker says OSB is OK for a substrate, but doesn't give thinset specifications for our case.

I spoke to someone at Lowes who suggested Laticrete Floor Adhesive, but I'm concerned about the "adhesive" part of that name. Isn't this stuff actually NOT supposed to stick the CBU to the OSB, but rather to just fill in the little spaces?

I also spoke to local tiling folk who said that putting the thinset under the CBU was overkill.

Help?
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Old 11-10-2008, 06:27 PM   #7
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You can use modified thinset for that. Versabond would be fine.
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Old 11-10-2008, 06:58 PM   #8
Brian in San Diego
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Quote:
Originally Posted by Devo
I also spoke to local tiling folk who said that putting the thinset under the CBU was overkill.
Perhaps those local tiling folk should read the manufacturer's instructions. This is taken from the James Hardie instructions for backerboard.

Quote:
3. Attach HardieBackerô cement board to subfloor

Apply a supporting bed of mortar or modified thinset to subfloor using a 1/4" square-notched trowel.

Embed HardieBacker cement board firmly and evenly in the wet mortar.

Use the fastener pattern as a guide. Fasten HardieBacker cement board with specified nails or screws (as listed in "Materials Required") every 8" over the entire surface. Keep fasteners 3/8" from board edges and 2" in from board corners.

Set fastener heads flush with the surface without overdriving.
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Old 11-10-2008, 07:23 PM   #9
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Welcome, devo.

I've combined your two threads here so folks can see the history of what you're working on and what's been previously asked and answered. Please bookmark this thread and use it for all your project questions. We can change the title to something more generic if you like.

Brian's correct, it's always a good idea to read and follow the manufacturer's instructions for installation of their products. James Hardi usta specify a modified thinset for installing their board, but now accept either modified or un-modified. So MMike's correct, also.

Keep in mind that the thinset is not intended to bond the CBU to the subfloor, but only to fill any gaps and provide a 100% footprint for the board. The thinset holds it up, the fasteners hold it down.

You are installing the CBU prior to the heating system, yes?

My opinion; worth price charged.
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Old 11-10-2008, 08:39 PM   #10
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Thanks so much for the responses (and for combining my project questions, CX)!

Yes, we've (mostly) rebuilt the subfloor using OSB and putting in extra support for the slate floor. There had been some rotting in the old one, so we pulled it up entirely and started from just the joists. On top of that we're planning to install the CBU. Then the heating system. Then the tile.

I entirely agree on following the manufacturer's instructions. But the problem I was having is that I couldn't figure out how to follow all of the manufacturers' instructions! Hardie Backer folks say to put thinset underneath (I read that, too) and that OSB is a fine substrate, but the manufacturer of the thinset (Versabond) specifically states that it is NOT for use over OSB. I think they even use the all caps like I just did!

Anyhow, we just bought some alternative thinset - Multipurpose polymer fortified-but-not-modified version made by Laticrete. This one doesn't say using it over OSB is OK, but it doesn't use all caps saying NOT to use it... We didn't have enough of the Versabond to do all our layers, anyway, and this came in a 25 lb bag, so this seemed like a good option. Any thoughts?
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Old 11-10-2008, 08:51 PM   #11
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Quote:
Originally Posted by devo
but the manufacturer of the thinset (Versabond) specifically states that it is NOT for use over OSB. I think they even use the all caps like I just did!
Yeah, that's a problem, Devo. No good answer for ya, either. Sometimes you just gotta do what you did and use a different product.

There is no good reason not to use Versabond in your application, and if you got holt of the right guy at CBP he'd tell you that. But all you can do is follow the directions on the bag. As you did.

Just wait 'till you wanna set some glass tiles over a waterproofing membrane.
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Old 11-11-2008, 01:48 PM   #12
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Hardie timing and warming mat installation tricks?

Still at it...

Today, we're planning to finish putting in the Hardie Backer (we've cut it to fit the room, but are taking a break to do our regular jobs for part of the day, and then coming back to install later), and then *maybe* also install the Warmly Yours mat on top of that.

So here are our questions.

1. Is it OK to install the Hardie (using the unmodified thinset we got last night, plus lots of CBU screws) and then install the heating mat on top WITHOUT waiting for the thinset under the Hardie to dry?

2. When we install the heating mat, I saw a great idea on another post here to get that layer flat, but wanted to double-check that I understood correctly. The thread was here: http://www.johnbridge.com/vbulletin/...stall+CBU+tile. The idea was to put in 4" strips of Hardie around the edges of the room and also anywhere else that the warming mat isn't covering (so in those areas, there'd be 2 Hardie layers). Then put the warming mat down in the single-Hardie layer area. Then basically fill the 1/4" deep area with the wires in it with thinset (Versabond, in our case), and use something like an aluminum screed to make sure the thinset is level with the two-layer Hardie areas. To me, this sounds like about the best suggestion I've heard to get the top of that warming mat layer flat without having to deal with SLC. But I'm a novice, so I'm basically looking for confirmation on this one. Thoughts?

Thanks again for your help so far (and hopefully for future help as well!). I promise I'll post photos when it's done!
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Old 11-11-2008, 02:06 PM   #13
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1) Yes.

2) You could use something besides hardi for the screed strips, such as old fashioned yard sticks, or wood lath. Stick them to the floor with carpet tape (double stick tape), screed the thinset, then when the thinset is cured, pull up the screeds, and fill those areas with more thinset. Using Hardi screwed to the floor poses the problem that the Hardi may "pucker" at the screws, or splinter, or delaminate. Using thinner screeds also saves thinset, so long as the screeds are thicker than the heat mat.
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Old 11-11-2008, 02:07 PM   #14
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1. Use not necessarily "lots of CBU screws" but the number in the fastener schedule specified by the manufacturer, devo. I don't know if any waiting time after installation has ever been specified in their instructions and presume none is required. But I don't do CBU floors. I'd recommend a call to their tech line if in doubt.

2. If you can get James Hardi to warrant that sort of use, go for it. I think it's a poor idea. If you wanna cut strips of Hardi to use as screeds for flattening your thinset over the heating mats, that sounds reasonable so long as you remove the screeds and fill those areas as well.

You try fastening narrow sections of Hardi to a Hardi installation you're gonna get a lot of screw-jacking, cracking, and generally poor fastening is my thinking. Just not a good application for that product at all.

My opinion; worth price charged.

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Old 11-11-2008, 03:18 PM   #15
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Hmmm...

Thanks for the advice on my question #2!

OK, so we should block out the area with something that's the right thickness (Hardie or something else) to help keep it flat, but then take that stuff up once the thinset has hardened and put in more thinset to fill those gaps.

One follow-up question: There's a pretty large area in the toilet nook part of the room that isn't going to have any warming mat (not that big, but maybe 4-6 square feet). Can we double-up the Hardie there to avoid using all that extra thinset? Or is that also a bad idea? We haven't installed the Hardie yet, so I suppose we could also get 1/4" plywood (do they even make it that thin???) to add that amount of thickness to the subfloor in that area... That would make the subfloor extra thick, but avoid the doubling-up on Hardie.

What would you do?


New Plan: I just called the Warmly Yours folks, and they said to use Liquid Nails every foot or so to adhere the mat to the CBU and then just use the flat side of a trowel to put a skimcoat of the thinset on top, 1/8" thick. So this is what we'll do, and report back.

Last edited by devo; 11-11-2008 at 05:02 PM.
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