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Old 10-08-2018, 11:24 AM   #1
dmpiz
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Replacing ceramic tiles with encaustic cement

Hi Forum-goers,

I just bought my first home and we have been working on updating our half-bath. One of the changes was to rip out the old ceramic tile and replace it with encaustic cement tile. I have read about sealing and whatnot and am confident I can handle that. I'm less sure about the subfloor and the height difference with the new tile.

The bathroom is about 20 square feet. We ripped up everything and found that the old vanity was sitting right on the subfloor while the tile was on 1/2" cement board. I planned to rip out the old cement board and put new cement board down on the entire floor. I am not exactly sure how to proceed. With the old tile being 1/4" and the new being 5/8", this should leave a 3/8" height difference. I have tried doing some research and it seems this is pushing it for a transition strip. Is there any reasonable way to lessen the height of the floor? Or is the height difference alright? Do I need to worry about deflection? Do I need to replace the old cement board or can I cut a piece for where the vanity used to be? Any other concerns or suggestions for a newbie?

Thanks for any advice you can provide. I'm getting a bit overwhelmed trying to understand all the issues!
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Old 10-08-2018, 12:15 PM   #2
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Welcome, Matt.

We'd first want to know exactly what you have for a joist system and subflooring, but if both are suitable the easiest way to reduce the finished floor height would to change from your 1/2" CBU to a 1/4" CBU which would be the recommendation of all CBU manufacturers for floor installations.

Those concrete tiles may/may not be as strong as ceramic tiles and I'd personally be inclined to treat them more like natural stone and provide a double layer of subflooring, but if you wanna take the chance on your floor, that's entirely up to you.

My opinion; worth price charged.
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Old 10-08-2018, 02:04 PM   #3
dmpiz
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Thanks so much for your response. I especially appreciate your patience since I am a bit clueless.

The joists are 2x8s, but most of them are doubled up right next to each other and several are cross-braced with 2x4s. They are mostly 10-12" apart except one pair are about 18, which have ductwork between them. It's a little hard to use the calculator on the site based on this, but it seems like it was built up to provide strong support.

The subfloor is 1/2" plywood. The vanity was just sitting right on that. On top of that on the formerly tiled portion is CBU. In total, there is 1" of whatever it is all on there. I'm not sure what exactly I'm looking at.

Overall, it looks like I have 1 1/4" to work with on top of the current subfloor. I'd be willing to go 1/4" higher than the exterior floor and transition without too much worry of tripping, bringing it to 1 1/2". Taking away the 5/8" for the tile, that leaves me with 5/8" to 7/8" to work with for thinset, additional subfloor, and CBU.

What would you suggest to go under the tile? And again, I really appreciate the help! I tried to attach pics of the joists from the basement and of the current CBU situation. Hopefully those will show up and be helpful.
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Old 10-08-2018, 05:34 PM   #4
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Matt, without knowing the unsupported length of your joists it's not possible to evaluate the stiffness of your structure and that's important.

You say the joists are "mostly 10-12" apart." Is that between the joists or center-to-center?

Even with the closer spacing the nominal 1/2" subflooring is inadequate for any kind of tile installation. And that would be especially true of the place where you have 18" between joists.

Let's start by finding out about the joist structure. Enter as much information as you can from your actual measurements. If the spacing is not all the same, use the wider spacing except for the 18" spaced pair and see if you're even in the right ballpark here.

The subflooring is likely to be the more important problem, though. You might wanna re-measure that or find a grade stamp on one of the panels to be sure of the thickness. And you need to know if it has T&G edges between the joists.

My opinion; worth price charged.
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Old 10-08-2018, 08:11 PM   #5
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Thanks again for your reply, and for sticking with me here. I really can't express my appreciation enough and I'm learning a lot. Like to research something more extensively before I buy it...

I found a stamp on the joists; they are standard grade douglas fir. I'm attaching that picture and one of the plywood's stamp. I wasn't measuring from the center of the joists before, but I have drawn up a diagram of what I've got since the widths differ. Hopefully it's legible.

In the diagram, the thick darker line at the top is the concrete block the joists rest on (making up the basement walls).

The dashed lines are approximately where the bathroom walls are and thus where the tile would be installed.

The joists are all 2x8 and there are 2x4s perpendicular to the joists indicated by diagonal shading. The 24" gap includes plumbing as that's where the toilet is, but the bathroom ends about 6" before the next pair of joists.

I still am not sure what the current 1" cement board layer is. When I pry it up I might have a better idea. I'm not opposed to putting in cement board again, even if it adds height, if it will make for a better result. Edit to add: I will have to come back to look at the joints. I'm pretty sure it's 1/2" thick, though.
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Old 10-09-2018, 02:21 PM   #6
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Once you get around to selecting the installation products, here is a blog post I wrote on encaustic tiles:

http://www.mapei.com/US-EN/tech-talk...ate=2018-05-22
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Old 10-09-2018, 02:28 PM   #7
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Your drawing still appears not to show the unsupported span of your joists, Matt. I see the 11'6" marking, but there doesn't appear to be a support for the dangling end of the joists? But at 11.5 feet you'd still be shy of the required L/360 deflection required by the ceramic tile industry according to our rather conservative Deflectometer.

The subflooring, if you are correct about the nominal 1/2" thickness would not be suitable as a first layer at all for a ceramic tile installation. The only way I would consider trying to use it would be if the top surface is almost pristine and could be glue laminated to a second layer of similar thickness. If there had been CBU properly attached to it, it's nearly impossible that it could be in such condition once the CBU was removed.

I can't tell anything from the grade stamp, I'm afraid. We've seen TECO stamps before, but they didn't look like that one. It appears from what I'm seeing in your photo that the stamp is saying yours is a CD grade interior glue plywood, something again I've never encountered. And I can see no thickness indication in the stamp, but there's a good bit of it I can't read at all. Perhaps in person you can see more of it.

If it is a nominal 1/2" panel, though, it's almost certain that it does not have T&G edges. Do you see any blocking under the panel edges from below?

Entirely up to you how you want to proceed, but I'm thinking you lack a suitable structure for the installation of your Encaustic tiles, even if they are in fact a fired ceramic type. I can't tell from over here if they're "cement" tiles or fired ceramic, but the 5/8th" thickness you describe doesn't sound like ceramic to me.

Finished height being a consideration for you, I'm thinking removal of the existing subflooring (after properly bracing under your wall) would be a necessary first step so you could start with nominal 3/4" T&G plywood after providing proper edge blocking.

The cross bracing, by the way, adds nothing at all as far as providing the necessary strength or stiffness of your joists and I'm not at all sure why you have so many spaced so closely together.

My opinion; worth price charged.
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Old 10-09-2018, 05:56 PM   #8
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Thanks again. The joists are supported at the 11' 6" mark, I just did not include that support in the drawing. I thought having the sistered joists and some of them being a little closer together might have helped with the deflection, but it looks like we have some work ahead of us.

From below, the plywood does not appear to be T&G. I can see a hair of light coming in between one or two boards from underneath. It's tough to measure, but I'm pretty confident at this point it's only 1/2". I also can't find any other stamp other than one saying "fortified glue" and a huge one of the company's name with no other information. There isn't any blocking along the edges within the bathroom area. The tiles are definitely cement.

At this point, I think I'm past my comfort zone. I will look for a contractor for some help. Thank you again for the advice and information.
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Old 10-09-2018, 07:12 PM   #9
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One way to determine subfloor thickness is to drill a small hole in an inconspicuous area and stick a tape measure through.
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