Charlie's first bath remodel...uh oh lol

[The Grateful Student]

Hey everyone. My name is Charlie and first off, I'd just like to thank all of you who contribute on this site. This is my first post but I've spent many hours here reading and learning so thanks a ton!

I'm looking for some experienced advice to help finish off my bathroom remodel, especially with regards to the floor. The house is late 1940's, single-level, raised foundation and in very sound condition structurally. I do not plan on keeping the house more than a year however I have no intention of leaving a time bomb for the next owner either. I'd rather do it right and that's why I'm here. We did a complete tear-out from ceiling drywall to the floor joists. My floor structure is 4x8 bearers on piers with 2x8 floor joists 16" OC. The bathroom has an exterior wall so the floor joists here run from the foundation to the first bearer which is only 7.5 feet away.

So here is my issue:

The finished floor in this house is the original T&G 7/8" hardwood which is the entire floor structure. So from the top of the joist to my finished floor is only 7/8". My goal is to tile the bathroom floor with stone and have the least amount of transition possible without compromising the integrity.

Here is where I am today:

Floor structure - All joists were dead level except one. I sistered a new joist to that to make it perfect. Knowing I needed to use the thinnest possible subfloor (5/8" by code) I then decided to put blocking between every joist 16"oc in an attempt to minimize deflection. So the longest stretch of dead-space anywhere is about 14". I then dropped 19/32" T&G CDX fir plywood down perpendicular to the joists. I wish I didn't choose CDX but I had a bad day when I picked it up and made a bad choice. Moving on. Put PL between that and the joists and then went insane with the screws (2" on edge and nothing more than 4" in the field).

Here is where I want to be:

Finished floor of onyx (3/8" thick) on top of a waterproof uncoupling membrane equal to the capability of ditra. I have two choices on site. Preferably I'd like to use a 5/8"x5/8" mosaic for the extra grout lines to prevent slippage coming out of the bath. I think this would hold up the best over the years also but too small for ditra. I also have solid onyx 12x12's (3/8" thick) that I could use but I'm worried about the hazard of a polished surface when it gets wet as well them cracking. We do get a few earthquakes here in LA. I do have a nice wet saw that I could use to cut them down however and I don't mind burning the time to do so. The bathroom is small so I think a 4x12 would probably be the best aesthetic option and then I'm in the ditra camp.

So my questions are:

1. If I go 5/8"x5/8" mosaics (the desired choice), what must I have as far as substrate on top of my 5/8" T&G and what is the absolute best waterproofing uncoupling membrane available for that small of a tile? Recall my finished floor is only 1/4" above the 5/8" T&G, so while a transition is inevitable I'd like to minimize it as much as possible.

2. If I go solid polished onyx, what size would you cut those down to and what grout thickness would give me a semi-slip resistant floor? Also, I would think this would be more demanding in terms of floor rigidness so what substrate am I looking at with this option?

Again, thank you so much to all who contribute to this site, both posters and experts responding. It is really an awesome resource.

[cx]

Welcome, Charlie.

'Fraid I can't make out what you might have for a joist structure at this point.

1. What is the type, size, spacing, and longest unsupported span of your joists?

2. Do we understand that you've removed the original board subflooring from the area to be tiled?

[The Grateful Student]

CX...you are a machine on these forums My opinion, worth price charged. It is an honor to have your advice.

Sorry for the confusion. Yes, my original hardwood (about 2.5" wide, 7/8" thick T&G) sits directly on top of the floor joists. There is no ply, or subfloor of any kind. When I crawl under the house, you see the bottom of the hardwood floor.

So to answer your questions:

#1 Floor joists:

Type - Unknown, but looks like fir to me. The house is 65 years old and I've only found one small crack in a single bearer under the dining room. Everything else looks unbelievably great.

Size - 2"x8"

Spacing - 16" OC

Longest unsupported span - 7.5 ft from the foundation wall on one end to the nearest bearer (however I tied all these joists together with blocking every 16" down the length of each joist)

#2 Subflooring: Yes, we pulled it due to the asbestos positive linoleum being attached to it. So, now there is new 19/32" T&G CDX glued and screwed to the floor joists and that is where I'm at. This new subfloor is only 1/4" below the finished hardwood floor in the hallway.

Thank you again!

[The Grateful Student]

I would greatly appreciate any input as to whether or not the following set-up would be likely successful or a complete and utter DIY failure

Current recap - Joist structure is 2x8" 16" OC with maximum unsupported span of ~7.5ft. Deflecto at 8ft = L/818. I also blocked between each joist every 16" in a crack-head attempt to make the floor as rigid as humanly possible. Current subfloor is T&G 19/32" CDX glued and screwed 2" on edge/2-4" in field.

I propose - Adding a 3/8" underlayment held by 1" screws as to only fully penetrate the new 5/8" subfloor. Then a layer of Noblebond EXT applied with a 3/32 x 3/32 x 3/32 v-notch trowel. Then Nobleseal CIS or TS (I won't need to overlap) and press into place with a 75-100lb roller. Then a layer of Laticrete 272 applied with a 1/4 x 1/4 x 1/4 square notch trowel. Then finally onyx stone mosaic which is 5/8" squares on 12 x 12 sheets with a very thin, almost dental floss like mesh (mosaic spacing is 3/32"). I will treat the onyx with 511 porous plus before laying it in the thin set. Grout choice would be non-sanded Polyblend from Homers. After that, a final coat of 511 Pourous Plus to seal everything.

Any red flags here?
Should I consider a 1/8 x 1/4 square notch trowel instead for the mosaic tiles as to prevent excess thin-set?
Also, does the Laticrete 272 deserve an additive?

Thank you.

[cx]

Really wish you'd used at least 3/4" plywood of a better grade for that dropped subfloor. Can't imagine the thinking behind using anything thinner in that application since there would be no height gain with any thickness.

The between-joist blocking for a span that short really doesn't gain you much of anything, but it doesn't hurt so long as it's not in the way.

The [b]absolute minimum[/b thickness you can use for the second subfloor layer in that application is nominal 1/2" exterior glue plywood with no face of grade lower than C.

If that's the recommended method of installing the NobleSeal, I've no problem with that.

Not sure why you'd chose an un-modified thinset mortar to set your tiles, but I think you'll find the Noble Company will require a modified thinset mortar meeting A118.4 for bonding tile to the NobleSeal. You could mix the 272 with Laticrete 333 additive if you like, but it might be easier and less expensive for you to chose a modified mortar from their line. They got plenty of'em.

Trowel size is something you're just gonna need to experiment with. If you use a 1/4" square notch with those tiles, I think you'll find you need to flatten the notches with the flat side of your trowel before setting the tiles. to get good coverage without excessive squeeze-out.

My opinion; worth price charged.

[The Grateful Student]

CX, Thank you for the reply! This has been an awesome remodel ride. Granted some mistakes made, all learned from.

I'm actually trying to limit a significant floor level difference between the bathroom and hallway. Maybe I wasn't clear. The polyurethane and dog hair on top of my hardwood throughout the house is literally only 7/8" above the top of the floor joist. It is simply T&G solid hardwood toe-nailed through the tongue into the joist with nothing in between. In the bathroom I had original 1940's linoleum glued on top of that so the floor was even with the hallway minus the thickness of the linoleum.

My thought process was at the time that the new subfloor/underlayment was likely to meet or exceed 1" alone, plus 3/8" tile, plus membrane and multiple layers of thin-set. I knew a transition was inevitable but I wanted to keep it as small as possible, so I went with minimum code in my locality which was 5/8. Totally a mistake, I agree 100%.

I'll put down some 1/2 ply tomorrow. I'll get the best grade I can get my hands on.

I have a bag of 272 already (we originally planned a larger format stone on ditra hence the unmodified). I can easily get some Laticrete 333 for it or just buy something else. What would you recommend?

Again, thank you CX. I'll happily buy you some ribs and a cold beer next time I'm in Texas.

[Houston Remodeler]

Charlie,


If this were my floor I'd seriously consider CX's advice and pull out that CDX. That's pretty darn important at this phase. CDX is the lowest of all grades commonly available, below what is required. Added to that the thickness chosen is bare minimum. Cracked tiles are a near certainty. I'd bet on it.

Consider this solution;

1- Add more joists if needed to meet the deflection.
2- Cover the joists with 3/4" T&G BC plywood
3- Primer the plywood
4- Install GreenSkin underlayment
5- Tile as usual.

This will put you about 1/8" to 3/16" over the hardwoods in the hall way.

[The Grateful Student]

At this point I'd probably rather put down a sheet of vinyl instead of tiling before pulling up the CDX because I already have the tub set, hardi up for the shower surround and my walls are painted. If that wasn't done yet there would be zero hesitation on pulling it out.

I'm lucky enough to have an exceptional lumber yard in the area. I'm headed out right now to see what they have so I can hopefully save the tile aspect of this job.

I'll keep you posted and thank you so much for the feedback!

[The Grateful Student]

So the retailer's website where I bought the initial ply subfloor has it listed as CDX, however I just verified that it is actually stamped Sturd-i-Floor 20oc Exposure 1 19/32" Underlayment.

Am I still tempting the fate of failure or can I continue on with stone mosaics by adding a second layer of 1/2" ply (BC or better) and the Nobleseal?

I'm reading here that for stone I need a minimum combined thickness of 1 1/8" between the two layers. I wish my head was on straight and did 3/4" of a much better product initially from the get-go, but instead I ended up with a learning experience.

Your advice in these regards are so appreciated. Thanks in advance for taking the time to do so.