Questions about my secondfloor bath [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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10-28-2002, 10:22 AM
Hi All ... I've enjoyed reading the posts here over the past couple of months, but before I tackle my third tile job I'm looking for a little advice.

I am renovating a second floor bathroom in a 1925 beach cottage that was remodeled and converted to four season several decades ago and well before I was here. Total bathroom square feet is 56. Area to be tiled is about 36 sq ft. A close-to-scale diagram can be found at

Upon removal of the old one piece fiberglass tub/surround unit I discovered the tub was sitting directly on what is likely the original 1x4 floorboards on 2x6 joists spaced approximately 16" on center (There are holes in the floorboards from an old plumbing job that I can get a tape measure in. Actual edge to edge spacing of the ones I can get to range from 17 to 14.5"). The current finished floor is sheet vinyl on top of 12x12 vinyl tile on 3/4 particle board, which is on top of the floorboards.

Here are the thoughts running through my head:

1: Remove the old flooring from the particle board, put new 3/4 sub floor under the tub area butted to the particle board, then add mortar, durock or hardibacker, mortar and tile and enjoy. (Because the new tub is 1" smaller than the old, there would be a seam between the 3/4 subfloors, but the cement board would cover that so it's not really a concern, I think.)

2: Remove the old flooring AND the particle board, glue and screw new 3/4 plywood over the entire area, then 1/2 backer and tile.

3: Remove the old flooring and particle board, glue and screw new 1/2 plywood over the entire area, then 1/2 backer and tile.

4: Remove the old flooring and particle board, patch the holes under the tub area, lay 1/2 cement backer directly on the floorboards and tile.

With option one or two, when I put the cement board and tile on top of all that sub-flooring it's going to create quite a toe-stubber at the doors. Options three and four lessen the toestub factor, but I am of course concerned about having a sound base to prevent the tiles from cracking (and if it matters, I was planning to use something along the lines of DalTile's "Octagon and Dot" floor tile, rather than 8x8 or 12x12 floor tiles).

Any and all comments and suggestions are welcome.
Thanks in advance.

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10-28-2002, 01:20 PM
First, what is the unsupported span of the 2x6 joists? Your total floor deflection must be less than L/360, so you may need some help here.

Second, with joist spacing exceeding 16" OC, backerboard is a non-starter. Go with Ditra. (Joist spacing can be up to 24") The only limitation is that Ditra requires 2x2 or larger tiles.

Third, Just say No to particle board! Get rid of it, and replace with 5/8" plywood bedded in thinset on top of the 1x4 planks. Then the Ditra, then tile. Your new floor will be only the thickness of the tiles higher than before.

Get me the span, so I can check on the deflection!

10-28-2002, 02:37 PM
Shoving the tape measure in as far as I can, and looking at the way things are finished downstairs, I would put the distance at between 9'6 and 10'.

John Bridge
10-28-2002, 04:40 PM
Hi Jeff, Welcome. :)

I took the liberty of editing your profile to light up your url. I also changed it from your email to your home page. Your email button is at the bottom of the post.

Of course, if you don't like it you can change it back. :)

I think Bob's plan is the way to go. Particle board is bad news.

10-28-2002, 04:45 PM

The sad news is that your floor joists will not support a tile floor. You would have to double each one of them the entire length to get the deflection to the minimum, and that's fudging just a little.

Since this is a second floor bathroom, adding a support beam is probably out of the question, but that's what it will take. If you can cut the span to no more than 6 feet, it would be fine.

John Bridge
10-28-2002, 04:48 PM

You might want to tear all the flooring off and double the joists.

10-28-2002, 05:21 PM
Hi John....

No problem on taking liberties with me. I won't tell anyone.

10-28-2002, 05:52 PM
Hi Bob, and John...

Thanks for the news, bad as it is. Just out of curiosity, how bad is the deflection from being acceptable? bb said "double each one" - are you talking 2x12s?

Unfortunately, ripping up the floor and sistering the joists with something larger and stronger is just not an option at this point (I assume that's what you mean by doubling, John).

There is a wall separating the bath from the bedroom which runs on top of several of the joists. I am not inclined to tear out two walls - the top and right walls in the diagram I linked to previously - and rip up the subfloor on the entire 19' width of the back end of the house just so I can have a few square feet of tile. Maybe some other time when I'm done doing all the other upgrades I need to do, like adding a third floor to take advantage of the view I have.

Ugh. Don't like the idea of vinyl flooring, but c'est la vie.

10-28-2002, 06:44 PM
Your floor is so floppy now that I would not want to consider adding a third floor and all the dead weight on top of those skimpy 2x6 joists. Hire a structural engineer before proceeding further.

10-29-2002, 08:27 AM
The deflection was just over twice the L/360 limit. Doubling meant sistering with the same size joist. Still would be "fudging" a little bit.

Could this be a job for one of those epoxy systems? The tiled area is just about the size of a sheet of plywood. Just thinking our loud...

Oh, yeah, what Scooter said about future plans.

10-29-2002, 09:25 AM
Double? Eeek!!

Well, it's not like I haven't done some fudging before on minor things around here.

What is this epoxy thing you hinted at? While I am hesitant to start ripping up the floor, perhaps that is an option.

Also, rather than sistering with traditional cut lumber, If I'm going to rip things up anyway would I be wrong to consider replacing the joists with LVL or wood i-joists? Is that even feasible? If I'm gonna make a mess, might as well make a big one.

Oh, and that third floor option is just a dream slumbering in the back of my head, and will likely only become a reality when I hit the lottery. And definitely I would take scooter's advice and hire an engineer and architect. And then a psychologist because I'm sure the whole process would drive me nuts.

10-29-2002, 09:57 AM
There are some epoxy mastics and grouts that some of the boys have had some experience with. (I'm only an engineer, the other guys are the experts) I'd like to get their opinion. You bathroom is on the end of the joists, so the actual deflection of the joists is minimized. Also, since it looks like the entire tiled area can fit on a single sheet of plywood, this may work. I'm hoping Todd chimes in.

As far as any other engineered wood product: Your problem is lack of depth. You would need steel joists to do much better that doubling the 2x6s. My point is as you said earlier, that this will be a whole lot of work just to place a few square feet of tile.

10-29-2002, 10:54 AM
Unfortunately, the tiled area would be 4'6 by 7'6, so a little larger than one sheet.

The reason I asked about sistering or replacing with an LVL is that I saw on there is a 5 1/2" LVL. Not sure if it would be applicable for what you suggested I do. Oh, specifically I was looking at the table on page 8 of the .pdf document at

I guess I'm just at that stage of trying to decide how big of a job I feel a DIY'er like myself can reasonably handle. Sounds like a lot to do all on my own, but if it makes things more solid and sound it would be worth it, eh?!

10-29-2002, 11:13 AM

The 5-1/2" trusjoists are 1.8 times stronger than the joist I used in your calculation. You needed in excess of 2 times stronger. If you were going to gut the structure, then you could use them, but you would have to space them about 12 inches OC. Or, you could use regular 2x6s doubled. At that point, it's about saving a few dollars one way or the other.

10-29-2002, 12:18 PM
Ok. Thanks for the figures.

Now, most of the sites I have looked at this morning regarding sistering have the installation done from underneath. Of course the last thing I want to do is tear down some perfectly good ceiling drywall. Anything I should be wary of if I attempt this from the top down, so to speak.

Also, let's say I do this. What would the advice be on the new subfloor? My inclination would be a double layer of OSB or plywood (staggered seams from one layer to the next, of course). Yes?


brain.... hurts.... thinking.... too... much.....

OVERLOAD. fffzzzztttttt!!

10-29-2002, 01:08 PM
If your brain hurts now, wait til you get to the tiling part! :)

There is no reason you can't install the sisters from the top. You may mess up the first floor ceiling when you remove the flooring and install the sisters. Fix that later. Use glue and screws for strength and to reduce the pounding on the existing joists.

You currently have 1-3/4". You will need a minimum of 1-1/8" plywood and 1/4" backerboard, which leaves you with 3/8" for the tile, and you're back where you started, height-wise.

OK, what happend to the Ditra, you asked? And didn't you talk me out of backerboard a little while ago?

Well, I'm glad you were paying attention. When you doubled the joists, the spacing problem went away. Now you can use backer board in the bathroom, and 2 layers of 3/4" plywood everywhere else. Slick, huh?

John Bridge
10-29-2002, 05:21 PM
what I meant was adding a 2x6 alongside each existing joist, but I think we're beyond that now. ;)


Click the button at the bottom of the reply form thats say "show signature."

10-29-2002, 07:20 PM
YOU may be beyond it, John, but I have anxeity levels that are rising faster than a dot com stock in the late '90s. I'm just hoping that if I do end up doing this the repaired floor won't do what the stocks did a couple years later.

Oh, THAT button? I figured y'all might be tied of that little old sig.