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Old 06-17-2018, 02:39 PM   #1
ARB63
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Bathroom Floor Prep - Re-Tiling

Hey guys,

As I prepare to re-tile my bathroom floor, a few questions have come up. Let me start by telling you the current setup and what I'm working with. Currently, as shown in the pics below, there is 1/4" thick ceramic tiles, butting up against a 4" wide marble threshold, with carpeting on the other side. All of these are installed directly on plywood (1.25" thick).

From everything I've read, installing tile directly on plywood is bad, so I was thinking I'd install 1/4" Hardiebacker, and then install a new threshold and new octagon/dot mosaic tiles on top of that. (Though I must say, the old tiles/grout held up perfectly fine on the plywood! Only issue is a crack in the threshold.)

Anyway, I have two primary concerns: (1) With the backerboard installed under the threshold, the height of the threshold will be "significantly" higher than it currently is (an additional 1/4" plus the thickness of the thinset); and (2) I expect that the edge of the Hardiebacker under the threshold will be somewhat visible.

I have to imagine this is a common situation; how is this typically dealt with? I'm hoping that there will be some good options that don't involve lifting up the carpeting. A couple of other notes/thoughts:

-- I was originally thinking Ditra might be a good option (with a lower profile), but I learned that it should not be used with small tiles, so I guess that's out.

-- Another thought was to install a new threshold directly on the plywood... Less than ideal, I know, but this would address the concern on the carpet side, and I believe the threshold will have enough height for the new tile to be at the height of the bevel. (The current tile falls ~1/4" below the bevel.)

-- Finally, should I even entertain the possibility of placing the new tile right on the plywood, like the current tile? (Does the fact that there are no cracks in the current grout suggest that the plywood floor is stable enough to handle this?

Thanks very much!

Allen
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Old 06-17-2018, 05:00 PM   #2
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Welcome, Allen.

While we (TYW) discourage the installation of ceramic tile directly to a plywood substrate, that does not mean it cannot be done successfully. It requires a properly installed plywood or OSB subfloor over a joist structure that meets L/360 deflection with joist spacing no greater than 16" on center and then a properly, and differently, installed substrate of a minimum of nominal 1/2" exterior glue plywood. Your tiles must then be properly installed using a premium grade thinset mortar.

If you can meet all those requirements, you can make a successful installation, but you'l almost certainly do better using a more appropriate underlayment such as the CBU you suggest.

But first you'll need to remove the tiles you have to see in what condition that leaves your current subflooring.

My opinion; worth price charged.
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Old 06-17-2018, 07:25 PM   #3
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Thanks CX!

While I don't have detailed specs of the subfloor material, I do know the joist spacing is 16" OC, and the success of the previous (i.e. current) tile installation (which was over 20 years ago) suggests that the substrate would do the job...

In thinking about the threshold height issues I raised, would you be inclined to lay the new tiles on the plywood, provided that it's in decent shape after removing the tiles? (I've pulled up some of the tiles when I recently replaced the tub, and for the most part, they came up without much difficulty and I've been able to scrape off any remaining thinset, so I'm reasonably optimistic that the plywood won't get wrecked in the process...)

Another idea I had is to remove the 1/2" top layer of plywood and replace it with 1/2" CBU ... Would that be a viable and/or recommended option?

Thanks again,
Allen
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Old 06-17-2018, 07:36 PM   #4
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If you remove the current 1/2" what are you left with? Keep in mind that CBU no matter the thickness offers no additional strength it is merely a a surface to bond your tile to.
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Old 06-17-2018, 08:10 PM   #5
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Allen, I would pay no attention to the height of the finished floor at the door. For interior doors you simply cut the bottom of the door to fit the finished floor.

And depending upon the location of the door you want to remember to leave enough space under the door for your HVAC to function properly.

My opinion; worth price charged.
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Old 06-18-2018, 06:58 AM   #6
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Quote:
If you remove the current 1/2" what are you left with? Keep in mind that CBU no matter the thickness offers no additional strength it is merely a surface to bond your tile to.
If I remove the 1/2" top layer of plywood, I'd be left with a 3/4" bottom layer of plywood. I hear ya re: CBU not adding strength... Do you think 1/2" CBU over 3/4" plywood (w/ 16" OC joint spacing) would provide a stable substrate?

Quote:
I would pay no attention to the height of the finished floor at the door.
Sorry, I wasn't as clear as I should have been... My concern with the height is not relative to the door, but rather, relative to the adjacent carpeted floor... If I were to lay 1/4" CBU over the existing two layers of plywood, the threshold would become 1/4"+ higher than it currently is, plus I believe the edge of the CBU would become visible. (But these concerns go away if I just lay the tile on the plywood, or replace the top layer of the plywood with 1/2" CBU... Just trying to figure out the overall best path to take...)

Thanks again; look forward to your thoughts!

Allen
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Old 06-20-2018, 07:09 AM   #7
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Hey guys,

Friendly “bump” to the top, as I’m still not sure what the best approach is for prepping the floor for retiling my bathroom… Currently, I have ceramic tiles laid directly on plywood (3/4” subfloor + 1/2” top layer), adjacent to carpeting, with a marble threshold transition. As I see it, I have four options, each with pros and cons:

1. Install new tiles (octagon/dot mosaic) on the same plywood (assuming that the old tiles come up cleanly and I’m able to achieve a smooth surface. (While it’s understood that plywood is not the best substrate, the current tile installation has had no problems.)

2. Install 1/4” CBU over the 1.25” of plywood. This provides the best surface for tiling, but the edge of the CBU may become visible where it meets with the carpet.

3. Replace the 1/2” top layer of plywood with 1/2” CBU. This would address the problem above, but would decrease the strength of the floor--although the 3/4” plywood subfloor still meets the minimum spec for HardieBacker.

4. Install 1/4” CBU over the plywood, EXCEPT let the threshold remain directly on the plywood. This would also address the problem in #2; but the tile surface would come right to the bottom of the threshold bevel, and possibly slightly above. (I’m thinking this wouldn’t necessarily be a problem though, as the tile surface would certainly be below the threshold surface, and the grout would smooth the transition, even if the bevel angle is effectively made shallower.

What would you guys do? Thanks!

Allen
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Old 06-20-2018, 06:44 PM   #8
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Allen,
I would leave the plywood. Rather than cbu you can use Statamat by Laticete. It is thinner than 1/4" and unlike cbu it is an uncoupling/anti fracture mat. I Think this would work well for your project.After installation pre fill the waffles flat and tile the next day.The limitation is the tile can not be smaller than 2".

If you are using smaller tile I would add the 1/4 cbu and remove the carpet at the transition and ramp it up a little to be flush with the new tile.
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Old 06-20-2018, 08:22 PM   #9
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You can stack the tack strip at the transition and then put a single piece behind it and cover it with your pad and once the carpet is stretched it will "Float" you will only feel it if you step directly on it. And you will not see the hump. If your transition is gnarly then do a triple where the tile carpet me and a double behind it with a single behind the all get covered with pad except the triple where the tile meet the carpet
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Old 06-20-2018, 08:39 PM   #10
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If you go with the 1/4" cbu use the screws,tape, and thinset, recomended by the manuf. Then you can apply a liquid paint on anti fracture membrane for cheap insurance. Use a thinset that is rated for porcelin.
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Old 06-21-2018, 12:17 PM   #11
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Thanks very much for the additional comments…

Some of the tiles are indeed less than 2” (the dots between the octagons are about 3/4” square) so it seems options like Ditra and Strata Mat are unfortunately off the table…

I suppose I hadn’t seriously considered pulling up the carpet and ramping it up, as I was unsure that this could be readily done with carpeting that’s already been installed… Is this something that I can do myself? (I’d consider myself a highly-competent DIY-er, but I’ve never installed carpeting before…) Can you provide any guidance on pulling up the carpeting without damaging it and then re-attaching it?

Also, would you consider option #4 above (install 1/4” CBU over the plywood but leave the marble threshold where it is on the plywood) to be a reasonable path to take? Prior to the ramping suggestions, this option was starting to look attractive to me…

Quote:
apply a liquid paint on anti fracture membrane for cheap insurance. Use a thinset that is rated for porcelin.
Mark, a couple of clarifying questions: can you tell me what you mean by "liquid paint"? And re: the porcelain-rated thinset, are you referring to the thinset used between the CBU and plywood?

Thanks again!

Allen
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Old 06-21-2018, 02:30 PM   #12
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If you're looking for a product to add over your plywood and keep height to a minimum, blanke permat would work.
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Old 06-21-2018, 04:34 PM   #13
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Thanks Ryan... I'm not familiar with Permat but I'll check that out as well!
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Old 06-21-2018, 05:35 PM   #14
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Laticrete hyroban and Custom red guard are two paint on liquid membranes. You can use cheap thinset inbetween the plywood and cbu. It is only to fill voids. The screws holdd it down. As far as leaving the threshold It is just a design choice.I have left them down when the owner wanted to keep the original and removal might break it. They usually protrude into the room somewhat so you might have to notch around it.
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Old 06-21-2018, 05:49 PM   #15
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Many times we have nailed down a row of cedar shingles under the carpet padding with the thick side against the threshold. The shingles are about 18 inches so it ramps the carpet up about 1/2 inch at the threshold.
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