Hello

We are in the process of bathroom remodel. We are putting a tub (no shower) against an exterior wall. Shower will be elsewhere.

We plan to tile about a foot or so along the top edge of the tub. Above that will just be dry wall. Will probably also put drywall below the tub just for insulation (there is fiberglass insulation between studs).

We were contemplating using some sort of backerboard here for the tile, but is that necessary? We will use that for the shower, but was thinking that just painting on some sort of liquid waterproofing stuff as a base for the tile would be adequate.

We live in Maryland, where it doesn't get real cold, but does get somewhat humid in summer.

I wouldn't bother with a CBU if there was no shower. You can buy a gallon of liquid waterproofing if you think you'll use the rest of it somewhere. For a job that small, I'd probably buy enough Kerdi to go up near the top of the tile. It would be cheaper than a gallon of Redgard.

At this point we know what we want to do, but are not sure what materials we should use from a standpoint of what is easy to work with, cost and availability.

The tub is acrylic, but is a drop in, so there will be frame covered with tile. What we put between the 2x4 frame and the tile is so far unknown.

The entire floor will be tiled. We currently have 2x10 floor joists. So what we put between the joists and the tile is also not decided.

The separate shower will be tiled on two walls with single glass screen on one side. Base will be tiled, probably the "old fashioned way" as the location of drain in constrained by vent ducting. As above, just what we put on the wall is undecided.

We are doing all the work to save money and while it can be a pain, we enjoy it.

As it is, it has taken several months to demolish the old bathroom and run new supply and drain piping. (Everything is being moved.)

Happily we live only two miles from one of those big box stores with an orange sign.

For above the tub I would just use regular drywall and coat the tiled area with RedGard just to be safe. You really shouldn't see any significant water or moisture on the small area above the tub.

The other option would be to use DensShield tile backer for above the tub and in front of the tub. It's already waterproof(except for the joints and seams)and is like working with normal drywall. You still need to waterproof any seams or joints on the DensShield.

For the shower you could use the Kerdi and regular drywall as Kman mentioned but you need to know that before you build the shower pan as you will also need the Kerdi drain for the pan which will also be covered with the Kerdi membrane.

Hybrid methods can also be used depending on your choice of construction materials.
We can help with any questions relating to that type of construction.

Have you looked at any the tutorials on the home page to familiarize yourself with the different shower construction techniques?

Once you come up with a plan, then ask about specific material choices and construction methods.

Oh, and BTW don't rely on any advice from any box store. In most cases there's not enough knowledge from them to do it right.

I have looked thru the picts in the "Shower gallery" http://www.ontariotile.com/showergallery.html and am somewhat bewildered at the variety of methods and materials available.

But I will study those tutorials and try to avoid asking too many Noob questions.

We are in process of a complete gutting/remodel of bathroom. It used to be two separate rooms with double sink and closet then single sink, toilet and shower. Closet is gone as is the wall separating the rooms.

Because of where we are locating the tub, toilet, etc... we are forced to place the shower in a particular corner that has a vent duct running thru it so the drain will NOT be in the center of the base, but kinda near a corner.

The dimensions will be about 36" deep by 60" long.



On this picture the 60" is left to right and the 36 the other dimension.

I was going to do the mud base thing, but having never tried that was thinking that Kerdi base and drain stuff looks pretty sweet. Especially as I'm leaning towards Ditra and Kerdi board.

Is there any chance it can be configured to work?

Or should I try to move the shower? Due how that vent runs up into the wall, moving the door isn't really an option and we can't put the tub over there.

ajrobson, It is better if you keep all posts related to the one project your working on in one thread only. There's less confusion that way on whats already been asked or answered.

I will merge the two together if you like.

With the drain in that location your only option is to do a mud bed. Shcluter trays do not allow for placing the drain anywhere else but the centre for showers or at the end for bathtub retro fits.

You may want to hire a pro for the mud bed or I'm sure with your skills we can guide you thru the process. It's not as difficult as it seems.

Sorry about the multiple threads. I guess a good subject line would be: "The bathroom from Hades" (not sure if that other word is allowed!)

Yes... please merge them.

And I was ready to try the mud bed thing. Doesn't look too hard (not to diminish the skills of the pro's) but since we have a LOT of work to do in this house, we are trying to do as much as possible ourselves.

And heck.. even if I mess up the mud bed and have to do it over, it's not the parts are a huge expense.

It actually looks fun. I think I might try practicing with the mud first, just to get the feel of working with it. What could be more relaxing than making mud pies!

Alan

Can I use this technique, using a Kerdi drain with a mud bed?

http://www.ontariotile.com/kerdi-showerpan.html

What are the advantages of using a Kerdi drain versus something else?

What you had seen was a mud bed with a Kerdi drain. And yes you can use this method.

The Kerdi drain has many advantages when used with a topical waterproofing system.

This system places all the waterproofing on the surface of the tile underlayment(walls) and the surface of the mud bed and curb.
When done right this is the best protection for your shower.
It also allows for quicker drying of the grout and drainage for any water penetration into the thinset layer.

Okay... in the interest of keeping the entire bathroom project in one thread...

I am getting ready to install my 2 layers of 19/32 plywood subfloor. One part of the room before was not tiled and consequently there might be a bit of a height problem from the room outside of the bathroom. That's if I put some sort of concrete board on top of the plywood for tiling.

Can I put Ditra right onto plywood? I'm afraid I'm still a bit confused by the plethora of products out there.

oh... scratch that ...

I've got the freaking Ditra Handbook I printed out last week for that info...

never mind..

Why are you doing two layers of 5/8" plywood? Are you installing stone?

If your not installing stone and you want to keep the transition height to a minimum,then I would use one layer of 5/8" or 3/4" ply plus Schluter Ditra.

Unless your joist spacing is more than 16", it's not absolutely necessary to add a second layer of ply. However, 5/8" ply is the bare minimum, so if you want a little extra insurance with minimum height, add a layer of 3/8" ply then Ditra.

I think someone recommended two layers of 5/8" but as we are not putting down stone and are going to use Ditra, I guess one will be enough.

The joists are on 16" centers with the maximum span about 10 feet.

Right now I'm in the process of preparing the perimeter of the room to attach the new subfloor.

I made the mistake today of getting a nice laser level and now know just out much parts have sagged.

I'm going to assume that the ideal subfloor is level, especially if there will not be a floor drain, which there won't.

I can't think of any reason to have any slope at all, at least not toward a wall.

Am I correct in assuming I should try to make the subfloor as level as possible?

Just a note: if I were going to put down only one layer of plywood, it would be 3/4" tongue and groove, glued and screwed to the joists.

How much out of level are we talking about? Slight variations are usually not a problem, but larger variations may require either sistering of joists to raise low spots or shaving off high spots.

There's also the option of support from underneath, but once the joists have sagged it can be a lot of trouble to get them back in shape. Sistering not only makes them level again, it strengthens them so they're not as likely to sag any further, provided it's done correctly.

Here is older picture prior to the plumbing being finished:



The room measures 8 ft wide (left to right in pict) by 12' long.

There is an overhang of about 3 feet under that wall with the window. There are 4 ft long sistered joist sections making up the overhang. It is the sistered joists that have sagged the most, between 1/2 and 3/4 inches.

I did just attach 3 additional sistered pieces. I'm afraid I didn't have the time to try to jack up the existing ones and am just going to assume that probably most of the sagging and settling is done. House is 42 years old. I did adjust the position of the new sistered joists to be at the correct height. I added these because there will be a 6ft deep soak tub at that end, though it will be centered over the supporting wall below.

But I did that before I obtained the laser level and fear at the corner on the right (where a section of joist was removed for the toilet closet bend) has an extra 1/2 inch of sag.

I guess I'll just do the best I can to get it as level as possible knowing that it will probably sag a bit more.

So the tongue and groove is needed even if the joints are on a joist?

Just to confirm, the "unsupported span" of these joists is 12', correct?

While you're well within tolerance for a ceramic tile installation, you do have several holes through the joists, the most troubling of which is the one on the far right that you mentioned.

It's difficult to tell from the picture how much of it was cut away, but if it has sagged considerably, it may have been cut too much.

To effectively sister a joist, 2/3 of it must be covered. In your case, with a 12' span, you would need an 8' sister, centered on the 12' run, glued and screwed to the joist. Adding a sister to one far end does little or nothing for the strength, since the weakest part of the joist is in the middle.

As for any potential problems caused by the holes drilled through, we're getting into an area that is beyond my knowledge. Maybe RC or one of the other guys will stop in and offer an opinion.

Okay... the light just came on as to what "supported span" means with regards to this bathroom. In the room below, there is just under 13' between the two walls that support the joists... duh!

However, the bulk of the sag is at that overhang, not in the center of that 13' span as far as I know.. at least it isn't obvious. But maybe not much is obvious to me.

That hole on the far right is part of the original plumbing.

I'm kinda leaning towards the 2 layers of 5/8 ply after all.

Thanks.

A picture is worth a thousand words! The last picture you just posted puts everything in perspective. Here's my observation from that photo.

1 What is the 3' overhang supporting? (load bearing roof or balcony?)I question the actual length of the cantilever because it's excessive. Can you post a photo of the exterior of your home where the cantilever is?

2 As your floor structure sits now (last photo) there is no way to strengthen that floor system due to the cantilever joists. Sistering a joist to the three joists in the centre area of the floor will do nothing. Because they are butting up to the ends of the cantilevered joists you now have a weak point with a seam between the old joist and the new joist. You will also be too far away from centering the sistered joist on the middle of the joist span. The ends of the sistered joists need to be ideally sitting on load bearing walls or beams. Short of that you won't get much suport unless you can get to within 16" of the bearing points. In your case that's not going to happen.

3 Any holes drilled thru the joists should not be more than 1/4 the joist depth and not less than 2" from the edges. You need to increase the joist depth for larger holes. Beams, header and trimmer joists or lintels are not to be drilled.

I would not worry about sistering joists as this will be of little benefit due to your existing structure.
Any holes that do not meet the above requirements need to be corrected.
Add your 2 layers of 5/8" plywood perpendicular to the existing joists. First layer is screwed and glued to the joists. Second layer is only screwed to the first plywood layer with 1-1/4 screws 8"OC Overlap the second layer butt ends 1/4 the joist span (for 16" span min 4")from the floor joists edges. The T&G edges need to overlap the first layer by 24" or half the width of the sheet below.

The overhang supports the wall and that side of the roof.

The overhang is actually only about 2' when viewed from out side with the lever being 28" to the supporting wall it sits on.

Just to make sure I understand what you mean by joist depth, these are 2x10's so the maximum hole size is 2.5 inches. There is only one which is that size (oval) which is where the old shower drain used to enter the closet bend.

All of the drain and supply plumbing are installed. Just how do I "fix" such a hole without replacing the joist?

I do also intend to add some additional support in that supporting wall as the tub will be on top of it. It's acrylic but holds up to 100 gal. Was thinking about either some 4x4's or a couple of jack posts. With vent duct and water supply lines coming up in there and drain stack also, there isn't much room.

I do hate this bathroom.

So to be clear, there is a bearing wall below your bathroom, 2' in from the exterior wall of the bathroom your working on.

Current building code for my area would never allow the structure that you have. The floor joists to support a cantilever must be continuous and the maximum allowable overhang for a floor structure supporting a roof load is 23" past bearing for 2x10 joists.
This may explain the sag or lower floor area around this location.
Since things have changed in 42 years and the house hasn't fallen down, maybe we'll just leave things as they are.

The joist depth for a 2x10 is actually 9-1/4" Calculations are based on that measurement, therefore the max. hole can only be 2-5/16". The more critical measurement is the distance from the top or bottom edge of the joist to the edge of a hole. Anything less than 2" should be structurally repaired. If the joist can't be replaced then a common fix would be to scab joist material about 2 or 3 feet long fastened over the damaged area.

You could place jack posts or more studs in the wall below, but since all shrinkage in the wall framing has already been done there's not much point unless you intend on trying to raise the wall. That would create more problems then you can imagine.

RC

Thank you very much for the explanation.
I will see what I can do about repairing that one hole.

And I'll make darn sure that we don't install a LCD TV in the family room below before we fill and test the tub!

As I don't have 5/8 T&G to use and all HomeDepot has is 23/32, that is what I will get. But two layers of that will be too thick so might just go with the one layer.

http://www.homedepot.com/Lumber-Composit...catalogId=10053

Should I put some 3/8 on top of that? They don't have T&G in that thickness.

Whatever you put on top doesn't have to be T&G. If you can stand the height, an extra layer is always better. However, 3/4" ply is certainly enough. Just make sure you run the long side perpendicular to the joists, and leave a 1/8" gap between the sheets. This goes for the second layer as well, if you choose to have one.

The 3/4" should be glued and screwed to the joists, and the second layer should be screwed only (no glue). Use the instructions from this article to install the second layer: http://www.schluter.com/5138.aspx

Excellent. I was thinking that if, in the future, the tile was to be redone, having that second thinner layer of sheathing would be easier to remove. Just rip up that sheathing.

Then again, why should I worry about a future homeowner... the previous ones certainly didn't.

Thanks for all the great responses. I do appreciate them.

Earlier in this thread I asked about using a Kerdi drain that will be offset from the center of the shower. I have seen some of those cool Schluter channel drains but the price is way too high. But there are other channel drains that aren't as expensive.

Because the drain has to be offset (due to HVAC duct) would not a channel drain be an ideal solution? Especially as this will be my first mud shower base and getting the correct slope around an off center draining is probably going to be difficult.

Of course I have to find a drain that will work and doesn't cost a fortune. But at this stage (still haven't gotten sub floor down...) I can still modify the PVC drain.

Any comments would be appreciated. Thanks

Alan

If you want difficult, then try and install one of the channel drains. The only one that's the least complicated to install in my opinion is Noble's Freestyle Linear Drain. http://www.noblecompany.com/Products/SheetMembranes/tabid/59/Default.aspx#products

It makes no difference where you place the Kerdi drain, unless it's too close to a wall.
Whatever the longest distance from a wall to the drain is the measurement you will use to calculate the rise per foot of run.
Once the Kerdi drain is installed you will transfer the rise per foot from the top of the Kerdi flange to the perimeter walls. This height will be the same level all around the perimeter.

The wall areas that are closer to the drain will obviously be at a slightly steeper grade (more than 1/4" per foot)but that should not affect the installation of your mosaics.

After looking where I would have to install a linear drain I don't think it would work well. If access was needed at some point, not only would the ceiling below have to be cut into but some bricks from wall around fireplace would have to be removed.

And I don't think really any of linear drains are cheap.

So ya'll gonna have to suffer with me using a Kerdi drain and mud bed.

Remember to take into account that the Kerdi drain flange is already pitched at 1/4" per foot. That's why RC recommended that you calculate the perimeter height from the outside (or top) of the drain flange.

Right now I am trying to finish up the process of leveling with shims, etc.. before laying down the sub-floor. I don't expect the entire room to be perfectly level due to the settling of the house.

I'm assuming that I should try to make the area where the shower will be level otherwise even if I follow the quarter inch per foot guidelines the water won't necessarily drain correctly.

Right now the "front" of the shower (where the curb will be) slopes down a bit from the back.

That corner of the room is next to the chimney and over the fireplace wall and hasn't sagged at all.

Immediately in front of the shower is the entrance to the room. So if I add shims to raise the front enough to level it, we will end up with a different slope across the threshhold compared to the room on the other side (hardwood floor).

It makes no difference how far off level the original shower subfloor is. When you transfer the 1/4" per foot slope measurement to the perimeter of the wall at the furthest point from the top of the Kerdi flange, this now becomes the mark you will use to level the perimeter of the mud bed all the way around the walls and curb.
This will create a continuous 1/4" per foot run down to the drain at any point on the shower floor. (If done properly)

Got more questions..

I am progressing far enough in the bathroom that I'm thinking of what actual Kerdi products I am going to use.

This is what I am planning:

1. Kerdi drain- no Kerdi base

2. Kerdi membrane for shower walls and I guess also on shower base

3. Kerdi membrane for wall above the tub and the sides of the tub .

3. Ditra membrane for the floor

Questions:

1. What do I do for the transition between, for example, the outside of the shower curb and the Ditra on the floor? Something has to get overlapped. I am guessing the Ditra should go over the Kerdi membrane.

2. I understand when putting the Kerdi membrane over something like drywall, that it is very important for the wall to be flat, or plumb to ensure a nice flat substrate for the tile. If, for some reason, the studs are such that it precludes the drywall being nice and flat, should I just use backer board instead? I was even contemplating putting backer board over the drywall (as the room on other side is an attic space and not well insulated).

Thanks.

1. I usually overlap Kerdi onto the Ditra on the floor a few inches to cover the gap. Unless you have seams in the Ditra within close proximity to the curb, the area will be waterproof.

2. If you want to get the wall flat, the framing needs to be fixed. You can take a bow out of stud (if it's bowed in toward the shower) by cutting a notch into it about half the depth of the stud, then push in on the stud to take out the bow. Then use a 2' or longer scab to hold the stud in place. You can sister a stud that is bowed out with a straight piece of lumber and some 3" screws. Backer board will not do anything to make the wall flat.

Can't help you on this, we always float out out shower walls which makes the issue of a non flat wall moot. As already stated the addition of 1/2" hardie will not solve the problem and yes the kerdie should go on top of the ditra on the outward side of the curb. Can't think of any other way to level out your walls. I know its easy for me to say because we use the old way, float everything out and with the introduction of all these new products it does create an issue. Sorry

I've finally gotten some time to get back to this project and am in process of setting the tub and finishing up plumbing for the tub.

Current plan is to use a bit of Kerdi Membrane along the top of the tub. The green board on the wall has been well primed. The tub is acrylic on fiberglass.



The greenboard goes all the way to the floor as it's an exterior wall. I am going to order the "tile bead kit" to use as shown. Even though this is a tub and should not get as wet as a tub, would it be worth it to run the Kerdi membrane between the edge of the tub and the stringer like this:



OR I could use some Redguard or some such waterproofing as mentioned earlier.

I want to do what will work the best and is easiest and most economical.

We've just started in this house so there will be more use for the Redguard eventually.

I am still planning on using Kerdi membrane on shower. What is the best substrate for it. I'm leaning towards using backer board of some sort.

Sorry for all the questions.

I'm going to back track a bit here. Without re-reading all the posts, is the tub in question being used as a shower? If is not then there's no need to go to all the work your describing.

You really do not need greenboard for a Kerdi membrane application. Regular drywall works just fine. However,my personal opinion is to never use drywall for the plumbing fixture wall. I use cement board for that wall. Eventually water ends up getting around the shower valve and running down the backside of the tile backer or soaking the core. Regular or greenboard drywall with Kerdi on the surface wont protect the drywall core or backside. At least with a CBU it wont disintegrate or get mould growth.

For the shower, Schluter still recommends regular drywall. You can use what ever you feel is going to work best. As I suggested above, a CBU works best for the fixture wall.

Thanks for the response Randall. I really do appreciate you taking time to answer.

Yes, the tub will NOT be used as a shower.. and at the rate I'm going maybe not even as a tub!

I know that greenboard really isn't any better for being water proof. But I do prefer wet sanding drywall when I can to avoid the dust and it does appear to stand up better to that than the regular stuff. Of course for this use that won't matter.

That certainly makes sense to use concrete board where the fixtures are.

I guess after looking at all the tutorials here where waterproofing is so important I just false assumed it would be for a tub.

This is what we have right now. On the left side the desk will extend all the way to the wall as a shelf.

So for the tub deck area there is no reason to waterproof anything? We can just put mortar right on top of the plywood/lumber?




At the time of my previous post it way my intention to butt the tile up against the side of the tub. But after looking at some pictures from American Standard I think it will look better to have that lip ON TOP of the tile like so:



The tub is acrylic and the rim can NOT support the tub. I guess the trick to get the height of the tub deck so the tile can be just slipped under the edge??

I would still use a CBU for the underlayment over the plywood on the tub deck. Not a good idea to bond directly to plywood. It can be done but that's your call. If you have some liquid waterproofing it wouldn't hurt to coat the top deck tile underlayment.

I think it always looks better to set the tub so that the tile just fits under the tub lip. You can get away with a very small bead of caulk if it's done right.

Make sure your tub feet or skid legs are set in a bed of thinset when you do the final tub placement.

The tricky part when doing it this way is to plan your layout to allow you to set all of the top (tub deck) tile first so that you can set the tub in place, make all the plumbing connections and then complete the vertical skirts.

I was going to use construction adhesive on the skids to glue down the few shims needed to level it. Won't that hold better than thinset? The tub isn't that heavy and while the plumbing will hold one end I'm afraid the other end might move.

Construction adhesive is just as good, but more expensive than a bit of thinset. The plumbing should not support any part of the tub, all feet should be shimmed to rest firmly on the subfloor. Ideally your tub skirt will end up 1/16 above the tiles and the gap is filled with translucent white silicone. This ensures that the tub weight never bears directly on the tiles.

i also water proof all tub decks, mostly to avoid potential moisture build up in the walls. This can happen if kids use the tub regularly and splash water around.

One idea I had was to screw a few blocks of wood to the floor so they would be positioned right next to the two skids that run under the tub and support it.

Then screw the skids to these blocks. I would also use construction adhesive.

Or would that be a bad idea?

I know the thinset or construction adhesive is supposed to secure the tub but I'm still worried the tub might move.

What are planing on doing in that tub?

Have you even looked at the manufacturer's installation instructions? There is never any recommendation of screwing tubs to the subfloor that I've ever seen.

Most manufacturer's just require the tub to be level and not bear weight on the tub rim. They also usually state that the tub should be placed in a bead of mortar to support the feet or bottom depending on the design.

Once it's siliconed there should be no movement.

As pisolpete mentioned,your plumbing should have nothing to do with supporting or holding the tub in place.

It's very important to calculate the finished height of the tub deck with tile so that the tile just barely touches the underside of the tub rim. If there's a gap at this area you can get movement or flexing of the top flange when people sit on the top flange while getting in or out of the tub,even if it's siliconed.

I've practically memorized the instructions. This particular tub does not required a mortar bed though it is listed as optional.

It's an American Standard 7236L/V and is acrylic over fiberglass. It is very strong and won't deflect when you step into it. There are two skids running along the bottom as legs.

I'm sure how I would put it on a mortar bed and still maintain the levelness. Would not the mortar have to completely contact the underside of the tub to be effective? Or would not the mortar on either side of the skids be sufficient (along with sufficient).

I know these are stupid questions. I'm just trying to learn and don't want to have to redo it.

I generally set the tub into several small piles of fairly dry topping mix. This allows the tub to be nudged around for about 15 minutes until I am completely happy with the position. it's quite possible to dislodge the tub from the mortar, so It is the silicone around the rim that actually ends up permanently securing it in place.

The mortar method is not superior to shimming the tub level, but it is generally a time consuming and tricky task to shim the back feet of the tub under a framed in tub deck. If you have easy access to all points that need to be shimmed, then that will work better for you. If you have the tub already and the floor is level, then you may be able to just place the tub directly on the floor and frame the deck to the correct height. I generally do not have that option.

Happily I spent enough time trying to perfectly level the floor so that I only need less than 3mm of shimming on the side of the tub towards the room to level it.

What if the drain is WAAAAY off center... such as in this picture:



Due to the placement of heater vent we can't place the drain in the center of the shower.. but more like a corner.

Would the height of the screed not be set by using the 1/4" foot measure as you mention

"measurement to the perimeter of the wall at the furthest point from the top of the Kerdi flange,"

That height is then marked all the way around the base of the shower. So at the point where the drain is the closest to the shower wall won't the pitch be greater than 1/4"?

Or, like everything else, am I not understanding something?

The furthest corner from the Kerdi flange @ 1/4" per foot will be the perimeter line to follow all the way around. And yes, the walls that are closer to the drain will be at more than the 1/4" per ft.
That's normal and I wouldn't worry about it.

This shower is similar to what your describing with the drain at one end. This shower is about six feet long.

Always wanted to do one of those with glass block.

What did you do, just make a 4" step all the way around and put the block on top?

The curb is KD 2x4 stacked 3 high. I use PL Premium construction adhesive to glue each layer along with deck screws. For this shower all the walls are regular drywall and the inside,outside and top of the curb is covered with 1/2" peramabase CBU. All CBU is set in a thinset bed and covered with Kerdi.

Got another question....

Currently the subfloor is 3/4 ply and I'll be putting a layer of 3/8 sheathing for tiling the floor. But I wasn't planning on putting the 3/8" under the shower base.

But now I am wondering if the 3/4 will be enough given that it will be on top of 2x10 joists on 16" centers.

This will be with a Kerdi drain.

Ok, I'm going to ask this again. Why are you putting a 3/8" layer of plywood down over the 3/4" T&G plywood.
I thought you were using Schluter Ditra on the floor?

Direct bonding to plywood is not a good idea. At the very least you should be using an approved tile underlayment type backer board installed per the manufacturers guidelines.

As for the shower floor, you only need the 3/4" plywood subfloor to install the mud pan over.

Unless your installing a natural stone type floor then the 3/4" T&G plywood is fine, but you still need a proper tile underlayment layer to bond to.