Advice - Preparing Bathroom For Floor Tile.

[jyl]

Ok, still on the project old house conversion to cafe here.

Bathroom is 5’ x 5’ roughly. Pulled out old tub, toilet, vanity, walls, floor, so it’s studs and old 3/4” diagonal wood board subfloor over joists. Spending quality time in the crawlspace (bathroom was built as a bumpout, outside of the house foundation) blocking the joists, may add a couple piers and posts if needed. But that won’t make the floor perfectly level, just solid.

Want to tile floor with large hex terracotta (some reasons for that aesthetic choice, won’t go into it here).

Question is how to prepare the floor for tiling. City requires a floor drain. If they see a floor drain, you know people (dumb people) will treat the floor as if it is waterproof. So I want to make the floor waterproof.

I’m planning to use Ditra membrane and Kerdi tape. Yeah, like a shower. That’s kinda for my own education - I’m going to basically build a shower pan and want some experience with this “new fangled” stuff (I last tiled a floor and shower when Clinton was President, it was all cement board and poured concrete shower pan then).

Question: would you keep the old subfloor, screw down 1/2” ply or 0.4” Hardie then apply self leveling? Or would you cut out the subfloor, add blocking around the perimeter of the room, shim the tops of the joists level, then screw down 3/4” or 1” OSB? Would you cut the 3/4” or 1” into pie shaped sections and shim to slope the floor to the center floor drain?

Assume you’re me, trying to do a good job for a building we’ll keep a long time, what would you do?

P.S. Next I have to do this to the kitchen, which has lots of floor sinks and floor drains. And that is over the finished basement, so it *really* has to be waterproof. So I’m kinda using the bathroom as a learning experience for the kitchen.

[john70t]

random: For walls it looks like purple board is better than green. IDK

https://multidrywall.com/blog/f/green-board-vs-purple-board-drywall-what%E2%80%99s-the-difference

[dad911]

Hard to evaluate your subfloor w/o being there.

I like Ditra & Kerdi, have been using it at least 20 years, no callbacks. But my tile guys do it right, and I'm there to make sure.

Make sure you follow the schluter directions. Especially with regard to they type of thinset (modified or not) they recommended. Wrong thinset can cause poor adhesion, trapped moisture leading to mold, uncured mortar, and will void the warranty.(modified needs air to set)

They used to have a guide on "wet rooms". I'd follow that.

If those drains go to the sewer system, do they make yo put in trap primers?

[gregpark]

I'm not a tile guy but I've done vinyl floor coverings when a floor drain is required or desired. The drain obviously needs to be lower than the floor surface. I'd leave the existing subfloor and put down a water proof membrane then install ½" Hardiebacker. Pin point where the drain goes and cut out a 2' circle of Hardiebacker. Slope the circle to the drain with high quality portland based cement. I use Featherfinish. Once the drain is installed caulk in the drain grate. Ideally you want the drain under an open counter or similar (you don't want a tripping hazard). You'll have to get creative cutting the tiles to the slope, it never looks great but you do what you gotta do

[908/930]

Not a pro, but I would likely keep the floor flat and run the slope to one side and place floor drain there. Would likely take it down to the joist and build up from there, will there be any problems with floor height transition to next room.

[gregpark]

^ if installing tile, the elevation of the floor in that room will be raised regardless of a drain. You can't just adhere tile to the subfloor.
You'll also need to install a P-trap. You won't be allowed to run it to the storm drain

[look 171]

Rip out the sub floor (not really necessary but I always feel that a piece of 3/4" plywood sub-floor is much stronger and better way to go) Lay waterproofing on top and use whatever brand you choose and their thinset. Run the thin waterproof membrane up the wall for at least 6-8". Assuming you drywall on top of that and not plaster for historical or restoration reasons, how would the base board be finished? I suggest the same as floor tile, not always the prettiest but it will be durable for a coffee shop where the cleaning crew will not care. As far as the floor is concern, it should be sloping toward the drain depending on the location. The problem with that is the P-trap must be filled with water at all times to keep sewer smells or bugs away. A trap primer should be code.

[Zeke]

I'll second going down to bare joists. You can do your slope on the joists. After making sure you got all the nails out, a power planer makes short work of sloping the tops of the joists using a laser as your guide. Better check and see what slope they want. Standard is 1/4" in 12 inches. But with ADA in mind they might have their own spec.

What I have done in the past (I think I took this plan from Trekkor) was lay 3/4 T&G flooring on the joists, glued and fastened with your favorite fastener. Then after pre-cutting all the cement board and laying it out, I used thinset spread with a 1/4" notched trowel but not square notches, don't need that much, and laid the CB into the thinset and rolled it out. I waited on fastening the CB until the TS was hard to eliminate any waviness. Then I countersunk CB screws. This is NOT a wet floor. But the CB over the subfloor set in TS does not flex. Solid as a rock.

I went down to the joists for height reasons. I was adding 1-1/4" to the existing joists which matched up to the original hardwood flooring in the house floor is close enough (3/4" plus 3/8ths wood). Add in some for the thinset and I got a close enough transition that it isn't noticeable . I may have shaved a bit on the joists to get a match, it was 2016 when I installed that floor, so memory fails.

AFA sloping design, direction and waterproofing, that's a job in itself. You likely want to avoid the obvious path in the room to use the facilities. I believe you need a 2" line and that's 2 plumbing units added to your sewer use. It will be interesting to see where you come out when the floor sinks are installed.

I know the aesthetics are discarded for this thread, but I have done low fired tiles in commercial and it was a disaster. High traffic areas were compromised within a year. I used porcelain tiles in '16. That or quarry tile for the deep red color of terracotta, not to mention again the transition problem with thick terracotta. I've got no use for the stuff. [/rant]

[gregpark]

You guys are turning this into an awfully big project! And if you cut the joists down for drainage you'll be cutting half the joist strength out on the low side of the room. For truly non ponding water, industry standard is a ¼" drop per foot (3" in 12'). And didn't his engineer insist on doubling joists that were already 16" on center in another room?

[look 171]

Milt is correct with the "Mexican tile". Its too soft for commercial use and it seems to love dirt. Once the sealer (top coat) wears off it will be a mess now add in wetness in a bathroom. It will be a nightmare within the first three month.

[jyl]

Ha ha, this is separate from that joist tripling thing. The bathroom was an addition, probably done in the 30s, it sits over a sketchy looking crawlspace with dirt and not a lot of discernible “foundation”. The engineer didn’t mention it, the city hasn’t mentioned it, I don’t want to attract any attention to it. It’s “pre-existing”!

There is a lot of sketchy stuff. Here is my son inspecting a joist in the kitchen ceiling, that was apparently inconvenient to some plumber back in the day, who decided to make the joist see-through. Well, I don’t want some inspector to see that. But I don’t want obviously new wood up there either. My solution was to take a 14’ length of old 2x10 I found stashed under the porch, where a century of hoarders have stashed lots of lumber, and sister the joist in a way that looks, I hope, like it’s been there for a century. I need to go up and dab brown shoe polish on the shiny nail heads.








We’ll be dropping the ceiling, obviously.

[john70t]

Originally Posted by jyl

It’s “pre-existing”!

You shouldn't have to hide at all.

In your own home.

see:
Grandfather clause.
Undue expense requirements.
The city knowingly hiding grants and/or rebate programs through advertisement. aka discrimination.

[gregpark]

I think this isn't his home but a business open to the public. And this is California- ADA bathrooms, wheel chair access, fire sprinklers and at the mercy of building and health inspectors for nonsensical stuff. And oh yeah, the taxes and insurance!

[Zeke]

Well, another advantage to pulling the old subfloor is to more easily repair the joists. However, subfloors run under walls so you would be breaking any shear that continuous subflooring provides being compress between the walls and the joists.

You need Jeff to come up there and spend a day. It would be worth 2wice the price of a plane ticket, lunch and dinner plus a decent consultation fee.

I mean it. I'd go but I can't leave. Jeff is more current anyway. Of all the nail benders here, Jeff and I seem to have done more old rat infested, squirrel nested, termite digested old work than most of the others.

[jyl]

Okay, I cut the old subfloor out. So now from joist to adjacent floor I have about 2” of height to play with. I’ll shim the joist tops and screw down 3/4” OSB. Some dry rot to fix.

Zeke, I am not sure about the floor drain details. I hired a commercial plumber and it’s his job to get them right. On the first floor, we have five floor sinks draining to a grease interceptor in the basement garage, everything in the kitchen and coffee bar drains to one of those floor sinks. The mop sink and handwash sink do not (if I recall correctly). A floor drain in the kitchen. The bathroom sink and toilet which do not go to the interceptor of course. Basement has a full bathroom and a laundry sink. Second floor has a kitchenette and a bathroom with shower. The plumber has been doing DFU calculations. The building has a 6” sewer line and the waste pipes I see going in seem pretty hefty. All the original plumbing is being removed, a full repipe. It will be new Pex and black plastic throughout, with copper stubouts.

The floor sinks are a hassle. The first floor is only 2x8 and the basement ceiling is low, so the standard floor sinks we got would have had people in the basement hitting their head on P traps. I had to order shallow stainless steel floor sinks, $1,700 worth, and waiting for them to arrive is holding up the work.

In general there is a lot of figuring out how to fit all this plumbing into the building.

The venting is a challenge, since all the existing vents are too small, and there are too few of them. We will be getting a roofer out to flash the new vents. In one case the old wall studs are too skinny for a horizontal vent run and I had to frame out a second 2x4 wall just for the venting.

The latest issue is the mop sink is right above the gas water heater and it’s exhaust duct to the chimney, I guess plastic pipe cannot be that close to heat. We decided to remove the water heater, which is quite old, and install a gas on-demand hot water unit which avoids this problem. There is plenty of gas capacity.

On the shear effect of the subfloor I’m removing (have removed) . . . the bathroom is a bumpout, extending past the foundation, the bumpout sits over a dirt crawlspace with some 2x10 joists on some, um, not very engineered looking supports. I think the bumpout and its structure, such as it is, are pretty irrelevant to the earthquake resilience of the building. It will probably fall off.

[jyl]

My afternoon.

[john70t]

Helping buddy out, three hours away up north, we had a half-day argument over replacing the soft floor sheets. Time drain.
(In a 10x20 kitchen, there was a couple inches dip in the center and it bounced.)

Even me paying for the new plywood wouldn't change his mind..

He finally relented. We doubled up the joists to level. I wanted to go deeper in the basement but no. Put down new subfloor. Glue and screw. Solid.
Put new cabinetry over that.
He thanked me later. Much later.

[look 171]

Thanks milt. I am kinda dumb, so you gave me too much credit then I deserve.

John,

That's little, tiny bath, 6x8 or 9'? I thought about shear on 1x sub-floor too every time we tear them out. Thing is, how many nails are actually doing its work plus, all the ends of the 1x sub floor are more then likely split to hell in a thousand pieces. So much for shear? If you are concern, I lay another 1/2" or 5/8 plywood over that but do pre-drill and sink some screws through that 1x sub floor to keep it from squeaking and glue the additional layer of plywood sub floor and hit the joist with longer screws. I like to leave me some room for the tile (therefor 5/8 plywood), thin set and whatever else you are planning for waterproofing. I am not a big fan of OSB for sub floor especially for a tile floor but I am sure its fine. For me, two layers 3/4 sub floor and you are good to go. Plus that gurder mentioned earlier and this thing aint going nowhere.

Again, if I am doing this, the sub floor would be out by now, fixed, block whatever joist needed, level and deal with the plumbing. Also, since you feel like this was a creative add on special, I always suggest and often do this for all my clients and throw down a couple of piers and a gurder. 4x4 would be far more then enough and much stronger then shimming, muti-level plywood sub floor. it will be good for your tile work later too, no flex=no cracks. Oh forgot, use large format tile thin set. Tiles doesn't sink.

I don't care if they are commercial plumbers but the calculation of the slope and drain is normally done by the tile man or contractor. Make sure he has the info of the slope or finish floor so he can run his drain. Its actually pretty easy, cut flush before the finish floor goes in. We do this all in house by the same person, so there's no issue there, but having to have someone else come in before and after a certain task is done, there's a lot of finger pointing so beware of the dimensions is all I am saying.

[gregpark]

"Okay, I cut the old subfloor out"

Are you considering the underlayment as the subfloor? Because the subfloor is still there.

[gregpark]

Cutting or shimming joists to tilt the floor towards the drain was suggested. I've been doing this stuff for a long time and I've never seen or heard of doing this except on an outdoor balcony or solid deck. An interior floor should be level IMO. Can you imagine a counter being shimmed up 3" on one end on a 12' wall?