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Unread 11-14-2021, 10:37 AM   #1
kimmeridgian
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old house floor and bathtub install

ok, first-timer here and i’ve been combing through and eating up posts on this forum. y’all are amazing!!

i started with removing everything back to to the subfloor/joists. i had to do a couple of sub floor board replacements but (much labor later) it is super solid and flat and over that i’ve laid quality 3/4” ply. i secured the underlayment to the subfloor with liquid nails and my nail gun. no gaps in the middle of the floor but the ply has some gaps relative to the wall that are 1 1/4”. too much? should i put some ply strips along the wall as filler? fill it with silicone?

as a note, the house is 100 years old and the walls are (were) lath and plaster. except for high up and behind the baseboards, they’d been replaced with drywall in the bathroom. the gaps relative to the subfloor are where the lath blocks things out. i’ll probably put kerdi in the place of the baseboard laths rather than trying to replaster just those areas.

my next steps are to dry fit the bathtub, seat the bathtub, then will be putting a Prodeso membrane (gasp, but hey, it is a pandemic and that was the easier membrane to get hold of for me) with a heating cable down (electrically heated floor). a slate floor tile will be going over top. the walls around the tub will be done with kerdi board and tiled. i’m sure more questions will follow… but first want to make sure the floor sounds good to go.
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Unread 11-14-2021, 11:04 AM   #2
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Welcome, Kim.

Too bad about your Shift key.

The perimeter gap may not be excessive, depending upon what you plan to install over that wood lath.
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Originally Posted by Kim
i’ll probably put kerdi in the place of the baseboard laths rather than trying to replaster just those areas.
No way you can use Kerdi in that application, so perhaps there is a misunderstanding. Whatever you use to patch the wall will cover part of that gap and if you'll have a baseboard of some kind, that will cover more of it and the same if you plan to tile those walls to the floor. If your KerdiBoard will go over your drywall in those areas, you're not likely to end up with any gap to speak of.

Unless that will be a heavy traffic area (not sure how you'd do that), I'd not worry about a small gap near the wall when I set my tiles. Not per the "rules," but wouldn't concern me.

Have you evaluated your joist structure to determine if it qualifies for a natural stone tile installation without any improvement? It's rare that a floor structure is suitably rigid for stone unless that was specified in the original plans and the age of your structure would suggest that not to be the case.

A natural stone tile requires a double layer of subflooring, regardless the joists spacing, and that is generally two layers of plywood. While not in compliance with the stone tile industry requirements, we've found that they will generally accept a good sawn-board subfloor as the first layer. You say you've patched your first layer of subfloor, but we don't know anything about it beyond that. And you say you've installed a "quality" plywood, but we don't know if that's high quality or low quality and what you really need there is an exterior glue plywood with no face of grade lower than C. That what you have?

Gluing the second subfloor layer to the board subfloor was not a good idea and using an adhesive from a gun tube makes it more suspect. The fact that you installed nominal 3/4" plywood as your second layer reduces the potential problem with the gunned adhesive, but without knowing just how much adhesive you applied, in what bead thickness and spacing, it's difficult to judge.

More information on your floor structure would help and some photos might make it more helpful. Use the paper-clip icon above the Reply dialog box to attach photos from storage on your computer.

My opinion; worth price charged.
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Unread 11-18-2021, 08:40 PM   #3
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thank you so much for the reply. very much appreciated.

read and took the notes from the forum when i bought the ply and told them NOT to give me anything worse than C faces and NOT to give me OSB… but (sorry, a bit sheepish about this) don’t seem to have written down what grades the faces ended up being.

the ply (3/4”) sits on a 1” thick rough hewn wood plank floor. not sure, but the latter seems to be a dense pine or redwood. appears original to the house and previously had a different (wood) floor overtop. had to take that original overlayer out -it was really uneven and covered in nasty thick glue once i removed the three layers of foamy detonated vinyl covering stuff. the rough hewn wood plank floor is sitting (nailed) on the floor joists (16” spacing). i nailed-gunned the ply to the 1” rough wood floor underneath with some addition of liquid nail. it was a thin layer drawn in broad curves… and sounds like i made a mistake in adding it… but maybe not enough of one to have to pull it up? it lays very flat (using my level). am hoping that those two layers (the rough planks plus the ply) together are what you mean by a double layer? but no, there has been no structural evaluation (minus generally, when i bought the house).

oh - and should note the bathroom is ~8’ x 8’ in total space.

didn’t fully appreciate the lath and plaster (but am learning to appreciate it). the bathroom appears to have very little of it left - most of the walls are replaced with variations of drywall. behind the baseboards was one of the only places with original plaster left. thank you for the correction. right, will use drywall there. i meant kerdi over drywall, but it doesn’t work, sense-wise.

yes… too tired for shift keys. saving my energy for the tiling magic that will be in my near future (i hope!). so far i’ve learned a great deal about power tools, being flat and square, and have enormous respect for the energy of people who do this as a career.

uploaded are a photo (sorry, they are selfies) where you can see the floor's original second layer (the uneven one that was coated in a thick glue residue), a photo after i got that all the way off, and a photo after the ply was on top (and toilet temporarily reseated). not sure if that helps?

unless the ply needs to come up, i am ready to seat the bathtub and then put down the heating/decoupling membrane (plan is to use -as per directions - polymer modified thinset) and put up Kerdi board around the bathtub. rebuilt a sturdy 8’ high back wall to enclose the third side of the tub.

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Unread 11-20-2021, 09:10 AM   #4
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The trouble with gunned beads of adhesive can be a situation where the plywood sits on top of the beads, preventing it from fully resting on the boards underneath. And in your case, Kim, the use of nails to mechanically attach the plywood to the board subfloor may exacerbate the issue since nails are not as good at drawing the ply down hard against the boards as are proper type and length of screws.

As to the ply itself, I recon most folks will install a mixed grade (C/D for example) with the pretty side up. Note, however, that plywood has a strength axis, and that is typically along its "long" edge, and should be installed with its strength axis perpendicular to the floor joists. From way over here it appears that may not have been done.

Filling in those areas where the baseboard was with drywall might be frustrating. Ideally you'd want to finish the seams in the usual way; tape and drywall compound, but doing so is likely going to create a hump and may prevent the baseboard from laying flat on the wall, which might also impact any miter joints. If the top of the baseboard will be above the seam you might consider not finishing it. As well, the filler pieces of drywall need to be in the same plane as the wall above or the same condition will result; the BB won't be flat. Shims behind the BB can help correct a lot of things be starting off with flat walls from the start will prevent some headaches later.
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Unread 11-20-2021, 10:32 PM   #5
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thanks, Dan. checked on the seams for the ply. the underlying floor boards run north to south, and the ply, which i laid over top in two 8' long pieces (each about 4' wide) runs east to west. think that means it is correct per your recommendation (minus the liquid nail addition... lesson learned).

put 1/4" drywall against the cleaned out laths and tied it to the studs with drywall screws. the covering sits quite flush (a little shimming was required here and there) with the wall above (also drywall). do i tape between the two drywall seams (the wall joining to the baseboard covering) and use joint compound (think this is what people mean when they say 'mud'?) to smooth it out?

also, bought this vinyl 'edging' product to run over the edges of my 8' tall wall that encloses in the third side of the tub. photo of it standing along that edge is uploaded. does this look like the right thing to put along the top and edges of the wall? also have seen a metal version. the ultimate intention is to tile on the 'tub' side (currently covered in kerdi board but not yet kerdi-banded - in the photo), then smooth and paint the 'non tub' side (a stacked washer-dryer lives there).

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Unread 11-21-2021, 09:52 AM   #6
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Kim, the floor boards themselves are run perpendicular to the floor joists and so, too, should the long edge of the plywood. Since that ply is already glued and nailed down it is, of course, up to you to decide it you want to pull it up. It may work fine as is, we can only share what the safe bets are.

Yup, drywall compound is often referred to as mud. As are many products that come premixed, or must be mixed, in a bucket. I'm just in the tail end of mudding drywall in my own bathroom remodel.

That vinyl "corner bead" is going to be a challenge, as will any corner bead of any material, given the very close proximity to the front of the tub. That spot is commonly referred to as the tub leg, and it should receive tile (see photo). If it is not tiled water will destroy that area in relatively short order. Generally recommended is the tub leg should be about 3" inches in width, and you clearly don't have 3".

An additional fun challenge; that vinyl corner bead will require a lot of mud to set it and it, as well as the all metal ones, will need a lot of mud to finish it, creating a build up of mud that might be difficult to deal with when you get to the top of the tub where it rounds over from vertical to horizontal.

If you cannot extend the end of that wall by 2 or 3 inches to create more space do seek out the paper faced corner beads. They, being much thinner than the vinyl or metal ones, will need much less mud to set and finish.

The patches for the base board look good. If the baseboard will cover the seams I would not attempt to finish them. If it won't then you've no choice.
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Unread 11-23-2021, 10:07 AM   #7
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ok, decided to leave the ply in place. this being my first time with this, have resigned myself to the fact that, while i wanted it to last for the long haul, there is a good chance it will be me retackling it some years down the road after more experience in doing it more correctly. disappointing, but experience seems my the best teacher.

added kerdi board to the outside of the wall (the tub leg) based on your recommendation, which means it will be a 2.5” width for the tub leg along the 8’ tall pony wall bounding the bathtub (not the 3”, but better, at least). and decided to plan to tile down that outer facing wall. there is 4” of kerdi board width from the tub the drywall on the opposite side, so that should be good.

haven’t decided about baseboards afterwards, yet. the old ones were quite tall and would cover my seams, but didn’t manage to get many of them off in undamaged condition (my original intention). something new is in order one way or another.

question: didn’t appreciate all the mortar differences (and still confused as to if there is really a difference in how people use the term ‘thinset’ vs ‘mortar’ for tiling contexts). i used the Mapei floor tile mortar with added modifier for under my membrane. looking back through the forums, this appears to have been a very uh… economical choice of mortars, though technically correct. is it of low enough quality that i should pull it out and replace it? it looks like their ‘uncoupling membrane mortar’ would have been a better choice but if no one has had a terrible end experience, at this point, i would be inclined to stick to my mistake, there.

the membrane appears to have set well (had to cut out and patch two squares where there was some lack of bonding, but those are fixed now), and feels solid and fully bonded under foot. filled in the divots on the top of my membrane and taped over the seams (using the unmodified Mapei floor tile mortar). if i don’t pull the membrane out and redo with a higher quality mortar under and over it (would necessitate having to buy a new membrane), can/should i set the floor tile (a slate) over top of the now-filled membrane with a higher quality / different formulation mortar (probably still Mapei brand as hat is what seems most available around here) or just continue with what i have (the unmodified Mapei floor tile mortar)?

plan to make a better choice for the tiling on the walls (which will be over the kerdi board) and have not yet chosen a product for putting the kerdiband over the seams.

thanks, Kim
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Unread 11-23-2021, 10:41 AM   #8
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Quote:
Originally Posted by Kim
(and still confused as to if there is really a difference in how people use the term ‘thinset’ vs ‘mortar’ for tiling contexts)
As well you should be.

We use and mis-use the term mortar in the tile industry a great deal. Sometimes there is clarification, such as with thinset mortar (thinset is a method, not a product), but deck mud is called mortar, and wall mud or fat mud is called mortar, and both floor and wall mortar is frequently called mud and even thinset mortar is occasionally referred to as mud. I'd be surprised if you were not confused.

That which is most commonly called thinset is a bonding mortar and is most properly called thinset mortar when use to bond something using the thinset or thin-bed method. No other proper use for such mortars. They are strictly designed for purpose of bonding.

If someone is bonding tiles directly to a still-fresh mortar bed using a sprinkling of dry Portland cement, that is not the thinset method. If that mortar bed is allowed to cure for at least 20 hours before the tiles are bonded using a thinset mortar, that is the thinset method. Such method having been developed within my lifetime, but now almost exclusively used in setting ceramic tile.

More than you wanted to know. More than you usually need to know, but a grasp of the concept will better allow you to sort out the commonly, and frequently incorrectly, mixed uses of the term mortar. And to further complicate things, those various mortars are frequently also called mud. But don't be confused with the compounds used to finish drywall, which are also frequently called mud. Those are a gypsum-based product and have no meaning or use at all in the ceramic tile industry.

For your current project, if you have successfully bonded your materials using the MAPEI mortars you've specified, I'd leave those areas alone. While those mortars may not be among the better A118.1 thinset mortars on the market, they may work in your application if you can get them applied well. I would suggest you use something else for the remainder of your work, though.

My opinion; worth price charged.
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Unread 11-28-2021, 01:25 AM   #9
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*super* helpful explanation, and double thanks for pointing out i’m not alone in my confusion.

ended up sticking with the mortar i started using for the floor and let it set for two days. then put the slate tiles overtop using Mapei Decoupling Membrane thinset (unmodified). was heavy work and started out with more mortar on me than the tiles… but got better. back buttered the tiles and coverage seemed near to 100% using my strange european trowel (pic attached). tried to clean excess mortar off the tiles best i could. had applied two coats of sealer before laying the slates which maybe helped).

sanded (grey Mapei) grout with maximizer up next. might try using a grout release over top before grouting (need to look up if it is safe for sealed slate, first). there’s a bit more space around the toilet flange than desired, but my intention is to fill that space with the grout unless anyone thinks that is a terrible idea.

wiped down joints where thinset squeezed through while the mortar was still wet but there are lots of deeper and more shallow joint spaces. do i need to evenly drill/scrape out the joint spaces before grouting or are variable depth grout joins ok?

best, Kim
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Unread 11-28-2021, 09:44 AM   #10
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Variable depths are ok, but you need a minimum of about 2/3rds the thickness of the tile for the grout, Kim.

As long as the base of the toilet covers the voids that's all that matters. No need to fill those voids with grout.
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