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Unread 09-20-2021, 03:09 PM   #1
Rp
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please help a first timer!

Hi everyone -

I recently became a first time homeowner. The house was built in 1928, was not always well maintained, and was flipped by a contractor who (as I've come to realize) did a lot of rather sloppy work, which has made every one of my improvement projects a new adventure... The silver lining, I suppose, is that I sure am learning a lot!

We (lady and I) are now re-tiling the guest bathroom. I'm specifically looking for advice on the subflooring, but will be happy for any additional thoughts.

We're using 8 x 9 x 5/16 hexagonal ceramic tiles. I measured the room at 33 sq ft and have 37.6 sq ft of tile. (I'd prefer more cushion, but the manufacturer only had four boxes available.) I'm planning to use Schluter Ditra membrane with Schluter All Set mortar and Kerdi tape for the walls and seams.

I was hoping to pull up the cheap square tile the flipper installed and find a decent subfloor. What I discovered is that they had apparently laid the tile directly on leveling compound, which they had poured on top of old linoleum, which was glued to old mini hexagonal tile, which sits on top of a cement bed. There is a significant crack running through the old hex tile and (I assume) cement bed (photo 1) and there is a good sized gap under the bathtub on one side of the crack (photo 2). It looks like there might also be active mold on/in the old tile layer.

I went into the crawl space to have a look at the underside of the subfloor. There is definitely significant water damage and what looks like active mold. (I'm planning to get this tested.) It looks like the flipper sistered the joists that run right under the crack and show significant water damage. It looks like they also removed some of the subfloor planks and replaced them with pressed plywood. Apparently they just removed the wood beneath the old cement layer and slid the new plywood into that space, leaving gaps between the old and new wood, as well (I assume) as gaps between the cement and the new wood. (See photos 3 - 5.)

How should I proceed?

If by some miracle testing indicates that there is no active mold, or if mold remediation doesn't require ripping out the cement and old hex tile, should I just leave it in place? If so, what should I put on top of the tile? Leveling compound, then modified mortar, then the Ditra?

If, on the other hand, mold remediation requires that I rip out the cement layer in order to clean / replace the wood -- or if that's otherwise what I should do -- what's the best way to rebuild the subfloor?

Do I need to be worried about the bathtub and tile around the shower? Is there anything else I should be thinking about?

I'm happy to post more photos if that would be helpful. Thanks in advance for any advice!

Rich
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Unread 09-20-2021, 03:40 PM   #2
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Let me see if I have this straight…you’ve got cement over the plank wood floor, over that there’s mini hex tiles, glued to that is linoleum, with leveling compound (cement based?) over that, that they tiled to? How much above the floor of the adjacent rooms is this bathroom floor??
From the crawl space picture, it looks like there’s 2x4’s as joists. Is that a correct perception? I’d think that that would cause a lot of flexing in the flooring.
Figure out what the base structure is before going too much further.
On the mold, that can usually be dealt with by steam and/or chemical treatments.
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Unread 09-20-2021, 04:10 PM   #3
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Thanks, Jeff. And yes, you've got the layering right. The house is a palimpsest. The tile we pulled was about a 1/4 above the hall floor at the bathroom door. Now that we've got it stripped down to the mini-hex, it's 1/8 to 1/4 below.

I may have misled you somewhat on the joists, due to my less than expert vocabulary. The main joists run north / south and are perhaps 4x4 pieces of redwood from the original construction. The 2x4's you're seeing in the pictures run east / west, across the main joists.

That said, there does seem to be significant flexing / shifting. I am in the middle of looking into foundation repairs that may include straightening the main joists and reinforcing or even changing out the foundation, but even then it's likely that this house will experience some flexing.

UPDATE: I just spoke with the field inspector of the mold inspection company that had already been out to my place for unrelated testing and agreed to look at photos I sent. He thinks what I'm seeing in the wood is mostly if not entirely discoloration due to water, but not active mold. He also mentioned that the pressed plywood is not a great choice as it absorbs lots of water. He said the absolutely safe option is to rip it all out, but given the difficulty / expense, he thought it would probably be enough to treat the wood chemically and then add a waterproofed layer above the mini-hex tile.

So my main question seems to be: What would be the best layer(s) to put on top of that mini-hex? Self leveling compound, then mortar, then ditra?
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Unread 09-21-2021, 10:25 AM   #4
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I am a total newbie to these sorts of things as well, just an FYI.

My question to you is, do you plan on living in this house for along time? Is it your forever home?

If yes, then you may want to just spend the money and rip it all out and get it done right! Anything you do could be considered a "patch" and will always be on your mind.

Maybe get a few estimates from the pros to see what they would recommend and the cost. You could demo a lot yourself to save money.

Just a thought...
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Unread 09-21-2021, 01:19 PM   #5
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Welcome, Rich.

A geographic location in your User Profile is often helpful in answering some types of questions.

Quote:
Originally Posted by Rich
The main joists run north / south and are perhaps 4x4 pieces of redwood from the original construction. The 2x4's you're seeing in the pictures run east / west, across the main joists.
For clarification, the 2x4s are in fact your floor joists. The 4x4 pieces supporting those joists would be support beams, and it would be helpful to know the actual size, spacing, and support spacing of those beams.

The patching material I see in your photos is not plywood, it's OSB. Nothing wrong with that material at all in that application if it's properly installed, which may not be the case in all your patches.

O really think you shouldn't be considering anything short of complete removal of most, if not all the subflooring, and starting over. That would also be dependent upon your finding the the underlying structure is adequate for your tile installation. That original mortar bed did not break to that extent for no reason at all.

My opinion; worth price charged.
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Unread 09-22-2021, 05:01 PM   #6
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Thanks, Colin and CX, for the welcome and info.

It's not meant to be the forever home, Colin, but we may be here 5 years or longer. If the costs aren't too high, I'd like to get the job done right. If I can figure out what the "right" way to go is, then I'll make the cost/benefit call.

As my profile now reflects, CX, I'm in LA. The earth does sometimes quake, humidity is generally low, and the difference between daytime highs and nighttime lows can be relatively drastic.

Thanks for specifying the terminology. The original redwood support beams measure a true 2 5/8 x 3 1/2 inches. There are four beams irregularly spaced at 6' (from wall), 7', 5.5', 5', and 5' (from wall); they are on foundation posts spaced at roughly 4'. (Permits weren't required in LA until 1933...) An additional and partial (2 foundation posts) beam has been added in the 7' gap to provide additional support. Also, the original redwood joists measure a true 2 x 6 inches; the sistered beams in the picture I posted are 2x4 fir.

The house does have foundation issues that I am planning to address; that may include straightening the support beams where they currently sag and reinforcing the foundation walls where they currently appear to have settled / shifted. Until / unless that's done, it's likely the house will continue to flex. I'm not yet sure how much of that I'll be able to afford in the near term.

CX, does that info change your opinion?

Perhaps it makes sense to tile on top of the current subfloor for now and then revisit the issue once I've done foundation repairs?

thanks
Rich
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Unread 09-22-2021, 05:13 PM   #7
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I think you'll end up finding removing everything to the joists will end up your easiest, longest lasting end result.

Old houses often don't end up with a flat or level floor, and trying to match up heights of the floors through the transition between rooms would be more easily handled by removing the subflooring, too.

If the joists/beams are adequate for tile in the first place, depending on the finished height you want on your floor, you might find sistering new joists on, or removing the existing ones and putting either them back or new ones such that they all align so the floor is flat and level, and the ultimate height after tiling would end up even with the hallway or other entrance(s) to the room.

Normally, you want at least an extra 10% tile, but when the tile isn't rectangular, it can be a little tougher to get everything to fit. You might be able to save a few sqft if you don't tile under the vanity, and just tile up to it. harder to get it to look good, so may need some quarter round or other trim there, or just go past the rim so it rests on the tile, but there isn't any under the whole thing. That would work if there's a floor to the vanity, but not if it's open, or you are just using a wall-hung sink.

The original tiled floor appears to have been done on a reinforced mud bed...that can work on less than ideal joists, but the cracks imply there was too much movement for even that, or it wasn't done right in the first place.
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Unread 09-22-2021, 05:22 PM   #8
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Thanks, Jim. If I were to remove the existing subfloor, can you (or someone) give me a sense of how difficult it would be to knock out the mortar bed under the mini-hex?

And if I were to do that, I'd then have to build back several inches of subfloor. Would I be pouring a new thick mortar bed? Or something else?
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Last edited by Rp; 09-22-2021 at 05:27 PM. Reason: additional questions
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Unread 09-22-2021, 07:57 PM   #9
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You could make a new mud bed, which would allow you to get the floor height exactly where you want it IF they allowed enough room to meet at least the minimum thickness. One reason it might have cracked is that it wasn't as thick as it should have been, among other possibilities.

But, sisters do not have to be installed with their tops even with the existing joists! You could set them at whatever height you want to end up with a suitable subflooring for the tile you want to install. Since you mentioned a ceramic versus a natural stone product, you could get by with a single layer of ply, but given the opportunity, it would make things stronger to put in two layers. The joists/beams provide strength along them, but the subflooring provides the strength in between them.

It may not be hard to crack the existing mud bed, but if it was done right, there is metal screen reinforcement in there, and that makes it harder to tear apart, and maybe someone who does that on a regular basis would give a better estimate of how hard it would be. It's heavy, and the metal bits can be nasty, so wear good gloves and strong clothes to protect yourself!
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Unread 09-23-2021, 02:25 PM   #10
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Thanks again, Jim. Sistering new joists that rise above the existing joists is a good tip.

You've also helped me realize that I made an error in my original post (which I can apparently no longer edit?):

I am using porcelain, not ceramic tiles.

My research on subflooring suggests that a major factor is keeping the amount of deflection within the working range of the tile. Is that the primary factor in determining an appropriate subfloor for a specific tile? And is the allowable range of defelction different for ceramic and porcelain?

If weight is a factor, I will be installing no more than 135 lbs of tile and probably closer to 120 - 125.

From what I've seen (including the library on this site), a 2" mortar bed is the preferred option, but a 2 x 3/4" plywood or 1" backerboard would also suffice for a subfloor. I'd be installing the Schluter Ditra on top of any of these. Is that correct for the porcelain tile I'm using?

I really appreciate everyone helping me understand!
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Unread 09-23-2021, 03:33 PM   #11
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Rich, your comment about your "sagging beams" requires me to suggest you correct all your foundation/floor framing issues before you continue with your remodel. Even were you to create the perfect subfloor over what you currently have, when you later decide to correct the deficiencies in your structure, you're quite likely to end up cracking your nice new tile installation.

I can't quite visualize your structure from your description, but It's possible all your unsupported spans are adequate to meet the required L/360 deflection requirements. Operative word there is possible. Redwood is very good in some applications, but it's not as rigid as some of the more common structural species. And if you've got some visual sagging, chances are you've got some spans that are longer than they should be.

To clarify, all porcelain tile is ceramic tile. Not all ceramic tile is porcelain. And no, there is no difference in the structural requirements for the backing material for the two categories.

A mortar bed is by far the best substrate for your tile installation if you can manage it. It's inexpensive, can be made dead flat and exactly the right height for your tile installation. It's also a very compatible substrate for thinset mortar application and, especially if a reinforced mortar bed is used, can help isolate the tile installation from movement in the framing structure. Can you build up the subfloor with more layers of engineered wood? Sure. But then you still need to top it with a suitable tile substrate and hope to get the height close to the desired height to match adjacent flooring. Lots of ways to skin that cat, but when you have room for the reinforced mortar bed, it's by far the best choice. The thickness, by the way, is a minimum of 1 1/4" and the maximum is 2" unless thicker is specified by competent authority. You can be that authority in your own project if you choose.

I'd give serious though to the mortar bed, but if you elect to do it otherwise, I'd suggest Jim's method of using taller joists to get the subfloor up where you need it to be while also stiffening your structure.

My opinion; worth price charged.
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Unread 09-23-2021, 05:20 PM   #12
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FWIW, most residential floors are designed for a 50#/sqft load, divided between dead and live loads.
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Unread 09-28-2021, 12:36 PM   #13
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Thanks again for the information and opinions, sirs.

CX, I'm posting a couple of pictures of the foundation directly under the bathroom we've been discussing; perhaps it will help you judge the deflection issue? The joist on the left side of the pics runs directly under the north wall of the bathroom. You can see the toilet drainpipe on the right edge of the pics; that's maybe 16 inches from the south wall. The west wall (with door) is between that pipe and the new support beam you can see in the first picture, and the east wall is on the perimeter of the foundation.

Unfortunately, I don't expect to be able to deal with the relevant foundation issues in the very near term. So I'm leaning toward installing on top of the mini-hex tile / cracked mortar bed. If/when I get the foundation work done and the new tile cracks, I would then go back and rip out all of the old subfloor, lay down a reinforced mortar bed, and put down new tile. I much prefer to do a job right the first time and not have to do it again, but my current situation appears to preclude that.

That said... If I were to put in a reinforced mortar bed, is it possible that it will "isolate the tile installation from movement in the framing structure" sufficiently that later foundation work will not crack the tile? That foundation work may involve jacking up joists and straightening beams, and perhaps replacing or reinforcing the foundation where it's cracked under the east side of the bathroom.

Also, do I understand correctly that the 50#/sqft load applies to everything above the joists (i.e., including the weight of the tile and subfloor)?

With continued thanks!
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