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Unread 11-18-2020, 12:26 PM   #1
DIYTina
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RedGard Over Liquid Backerboard?

Hi All,

First-time poster, long-time lurker here .

I’m getting ready to replace the floor tile in my kids’/guest bathroom. The subfloor is wood, and I can tell the floor needs to be leveled as there is a slight dip in the middle of the room.

My plan is to use Henry 542 Liquid Backerboard (after applying the 554 Liquid Primer), and then I would like to install a waterproofing membrane, since this is a kids’ bathroom and water tends to get splashed out of the tub. The tile I’m installing is 1” hexagon mosaic tile, so I understand that using Ditra and the like is out. To make things simple, I would like to use RedGuard, but my question is:

Can RedGuard be applied over the Henry Liquid Backerboard? I can’t seem to find an answer in the specs for either product.

If yes, I’m assuming the RedGuard would go on after the Liquid Backerboard (not before)?

Or, if you think I’m making things too complicated and don’t need a waterproofing membrane for this application, please let me know!

Thank you in advance for the advice!
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Unread 11-19-2020, 06:23 PM   #2
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Hi Christina and thanks for joining the forum!

You can put Redgard over LBB. Ardex (owns Henry) would probably prefer that you use their liquid waterproofing but the Henry's product and Redgard are both on the shelf at Home Depot.

My personal opinion is that Redgard isn't required but certainly it won't hurt anything. However, I typically would just tile the floor right over the self-leveler.
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Unread 11-19-2020, 06:31 PM   #3
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Welcome, Christina.

Your bathroom floor would not normally be considered a wet area in the ceramic tile industry, but the industry also says that any area you know will get wet should be treated as a wet area. Your RedGard, or similar, would be applied immediately under the tile installation and per the manufacturer's instructions.

There is no technical reason for you to level your floor. Your ceramic tiles don't care a whit about level, they care only about flat. Your one-inch mosaic will follow every rise and dip in your floor, so it you want a flat tile installation you must start with a flat substrate.

You have evaluated both your joist structure and your subflooring to determine that both are suitable for a ceramic tile installation without any improvement?

My opinion; worth price charged.
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Unread 11-20-2020, 01:51 PM   #4
DIYTina
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Thank you both for your advice - I really appreciate it!

CX, my apologies for the naïveté, but what should I be looking for to ensure that the joist structure and subfloor are acceptable for ceramic tile? The floor previously had ceramic tile installed, but so far that’s all I have to go on. Thank you again!
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Unread 11-20-2020, 03:15 PM   #5
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Naiveté is something we've all got some of, Christina, only our subject matter differs. No apologies needed.

If you'll open our Deflectometer in the dark blue bar at the top of the page you'll see the information you need to evaluate your joists. Unless, of course, your joists are engineered wood rather than dimension lumber, in which case you need to consult the manufacturer to determine their deflection characteristics.

For the subfloor you need to know the type of subflooring, the thickness and the joist spacing.

Photos are often helpful.

My opinion; worth price charged.
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Unread 01-23-2021, 12:49 PM   #6
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Water Damage on OSB Subfloor

Hi All,

I’m planning to re-tile my guest bathroom floor (on the second floor of my townhome). I’ve ripped up the old 4x4 ceramic tile, as well as the PermaBASE underneath it. The subfloor is OSB, 3/4” thickness (I believe - I’m having a hard time measuring the thickness without putting additional holes in the floor).

My plan for the install was to add another layer of OSB or plywood, patch the seams with Henry Feather Finish, prime, apply Henry’s Liquid Backerboard, and then apply a coating of Ardex S 1-K before the thinset and tiles (which are 10x12” sheets of 1” ceramic hexagon tile).

My problem is that there seems to be water damage on the area of the subfloor around the toilet flange. I tried poking some spots in the affected area with a screwdriver, and it didn’t go too deep - about 1/8” maybe. I’ve attached pictures of my subfloor that shows the damage. I’m wondering if I have to rip out and replace this part of the subfloor (which I would really like to avoid, as I feel it’s a bit beyond my capabilities), or if I can continue as planned by installing another layer of OSB or plywood? Because of the kind of townhome that I live in, I have no basement access, attic, etc. where I could examine the subfloor and joists from below.

Any advice or recommendations you have would be greatly appreciated! Thank you in advance!
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Unread 01-23-2021, 01:51 PM   #7
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Christina, I've combined your new thread with your original thread on this bathroom for continuity. A moderator can give it a more generic title any time you'd like to suggest one.

The problem with the wet OSB is that once it gets wet it expands and never recovers its original size or density. Doesn't sound like yours is substantially damaged, but it's difficult to tell from over here. While it's possible you could add a second layer of nominal half-inch exterior glue plywood, the fastener holding capability of the OSB in that area has been significantly diminished.

Judgement call. You're the judge.

My opinion; worth price charged.
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Unread 01-23-2021, 01:58 PM   #8
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Thank you very much, CX! Are there any ways I can assess the extent of the damage to the OSB other than the poke-with-a-screwdriver method (given that I can't examine the joists and subfloor from underneath)?
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Unread 01-23-2021, 02:05 PM   #9
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Not really unless you've encountered water damaged OSB in past and can compare. You might get a small piece of half-inch plywood and just try screwing it to the floor in that area and see how the screws hold. It might be OK, but that stuff (OSB) really looses its composition pretty quickly with water damage. Yours may be only surface damage, but I can't tell from over here. Even with my glasses on, eh?
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Unread 01-24-2021, 11:16 AM   #10
DIYTina
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Thank you, CX. I tried your suggestion last night and my husband was able to pull the piece of screwed-down plywood off of the damaged subfloor (womp womp). So now on to find a contractor to replace that part of the subfloor . . .
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Unread 01-24-2021, 12:02 PM   #11
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And the reason you and hubby wouldn't just do that yourownselfs?
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Unread 01-24-2021, 12:22 PM   #12
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I really would like to do this myself, but I don't have a good understanding of the floor structure (I've never replaced a subfloor before). There are no discernable screws or a pattern of nails along the edges of the boards, so I'm thinking this means the OSB was nailed and glued to the joists? I was only able to find two joists by thumping the floor - they run horizontally in the pictures I posted - and seem to be 24" apart. Finally, what has me really confused is that when I look at the seams, the OSB only seems to be 3/8" thick and then there's a layer of something else beneath it. I've attached a picture showing this to the best I can capture.

Any thoughts on what might be going on?
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Unread 01-24-2021, 12:44 PM   #13
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That appears to me to be showing the tongue of a long edge of your T&G OSB panel, Christina, which is a good thing except that the gapping appears a bit wide.

Now that we know you have 24" joist centers, I'd say you must have the second layer of subflooring, rather than it just being preferred.

As for patching your existing floor, I can't really comment much without being on site, but there's always a way to do it. Some folks might tell you not to bother and to simply install your second layer over what you've got. That decision should be made by she who is on the floor making the observations. Removing glued-down subflooring is difficult and, depending upon just how well it was done, possibly damaging to the top chord of what could well be engineered joists.

It's a judgement call. You and Mr. Christina are the judges, eh?

My opinion; worth price charged.
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