Wow! This site Rocks, but I am still a bit confused. I bake cookies for good advice!! [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-22-2008, 01:44 PM
Good Day. I have spent my free time the past two weeks enjoying the site and learning much. I am a new DIYer. I have a 1906 house in Midwest Indiana. I have gutted a 2nd floor bath, to studs and joists. Once I started I couldn't stop!! My poor husband is patiently showering under a garden hose in the basement until it's all back together.

Please forgive my ignorance, but after reading about 8 threads regarding subfloor I still have a few questions.

Let me paint the picture. I have 2X8(actually 1 3/4 X 7 3/4) floor joists 16" OC. The second floor is supported by a first floor center wall which the 2nd floor bath straddles, half on each side. The only other support is the exterior walls which are 13 feet on either side. I used the deflecto calculator and entered in these amounts and of course it says is NOT ok to install tile. My husband swears I should only enter the bathroom measurements, which is 8 feet(he really wants it to say Marble is OK!).

The entire second floor was 3" pine t&g. No subfloor, just 3" t&g on the joists. It is everywhere, even under the walls(except the Center support wall). I cut out the all of 3" pine t&g to access all plumbing so I could correct the leaky problems and reroute wastelines and water supplies. So now that is all done! Regardless as to what the deflecto says, I need a floor. What kind is where I am lost.

1.) Can I plan for tile?
2.) If I am correct and we may not, is there a fix so he may have his tile?
3.) If he is correct and may have the tile, please advise on subfloor. I understand what not to buy, how to lay 1st layer perpendicular, to use lots of glue(it's my friend right?), use hot dipped galvanized not plated screws, to leave little spaces.

Then I'm lost! I want to marry into the 3/4" t&g at the threshold with as little transition as possible while maintaining integrity.

What thickness ply subfloor? What comes next, more subfloor, thinset or underlayment(cementboard)?

If the bottomline is no tile...can you please help me tell my husband he's wrong and he should continue being the great guy he is and be patient with his demo lovin' wife!?!

If anyone has time to answer, please type slow! I am just learning.

BTW, where do I send the cookies?


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02-22-2008, 02:01 PM
Sorry, unless you beef up the joists, you aren't destined for tile, let along stone on the floor in the bathroom. The size of the room has no effect on the deflection - the length of the joists underneath are what dictate things. If you were able to double (sister) up the joists, you'd get to a point where you could do ceramic. The sisters need to span at least the middle 2/3'rds of the unsupported length.

Schluter is readying a second version of Ditra. It might allow ceramic on your floor, but I haven't seen it available yet (haven't really looked, but figured I'd hear about it here when it was ready for distribution). They were still running tests last I heard. It is thicker and can absorb more flex than the original product (which will remain around). To simulate the effect of the thicker stuff prior to committing to build it (quite expensive to make the tooling), they installed two layers of Ditra. This might work on your floor, but you'd not get a lucky do you feel?

A stone tiled floor requires two layers of plywood. A good starting point for the first layer is 3/4 T&G, glued and ring-shank nailed or screwed (deck screws, not drywall) to the joists. Then, a second layer, minimum 3/8, more is better, is screwed on top of that, with the ends and edges offset from the layer beneath. You won't need to worry, as your floor isn't strong enough to handle it.

02-22-2008, 02:11 PM
Thanks for your quick answer. Gives me time to make a great dinner and break the news.

crow wing
02-22-2008, 02:14 PM
Jim is right on you need to sister the joists add 2 layers of plywood then your ready to rock. it doesnt pay to take short cuts.

02-22-2008, 02:23 PM
The only real way to do this is probally to rip out the ceilings below huh? The floors above aren't an option.

This same deflection probally explains the cracks in the ceilings at the middle point of the joists then too.

If I went to the exteme of ripping out ceilings below to beef up the joists, Would I need to both sides? Since the bath straddles the center support wall below?


02-22-2008, 02:25 PM
Another crazy lady question:

Could I install the floors as directed and then beef up when I move to the next project of tearing out the first floor? Or do I need to tear up my whole house now? hee-hee

02-22-2008, 02:35 PM
Yes, you'd need to do both sides at the same time. SOmetimes it isn't very easy, as there may be ducts, wires, and pipes in there that make adding a sister to each joist really tough, so you might be rewiring as well. A plaster ceiling, like tile, doesn't like deflection.

02-22-2008, 02:41 PM
Luckily no ducts and only one light fixture. Just a husband scared out of his mind about what he might come home to next! Thanks again.

02-22-2008, 02:55 PM
I think you might want to wait for a second opinion on the joist stiffness question. I believe you indicated that your bathroom is straddling a support wall underneath (is the first floor support itself supported by a foundation?). I think this could change things, and I'm not sure the deflecto can exactly address this situation. You might try to get bbcamp, the engineer, to comment.

02-22-2008, 03:04 PM
Thanks for the input. The 2nd floor bath straddles the 1st floor center support wall. This 1st floor center support wall is supported below grade with an approx 7 1/2 foot block wall the entire span down the center of the house with the exception of a small doorway which is only supported by a 2x6 laying flatwise. This doorway is 2 floors below bathroom entrance area.

How would one get this information in the right hands for an opinion?

02-22-2008, 03:20 PM
100_2234.jpg This is the 'hole' thing.

100_2235.jpg This is the floor.

Looking at the center support(towards the left) the joists run 64" to the left wall and 22" to the right wall. The joist support is not exactly centered in the bath.

We will be tiling about a 7X10 space minus a 48" X 35" space in the corner for a shower.

Am I concerned over nothing considering the size?

02-22-2008, 03:34 PM
Welcome, Handy. Please give us a first name to use. Go to the UserCP above, find Edit Signature and enter it there. :)

Your photos didn't appear. Maybe try again. We like pichers.

But they won't likely tell what we really need to know, which is the longest unsupported span of the joists under the area to be tiled. If there area support walls below the joist, they would shorten the unsupported span, eh? If there is a support beam in the center of the tiled area, you must know the unsupported span of the joists on each side. And in the case of the support beam in the center, you must also note how the joists are connected there if they are separate joists going in each direction.

I think I disagree with the others on the need for two layers of plywood on top of your existing sawn board subflooring. You must have two layers of subflooring, but that board floor, if it is nominal one-inch and in good condition, would serve as the first layer.

My opinion; worth price charged.

02-22-2008, 04:15 PM
Ah CX, you missed that she's removed it to do the plumbing...and that it's 13' to the outer walls. There isn't any subfloor in the bathroom now...

02-22-2008, 04:24 PM
Thanks, Jim. First thing I've ever missed on here. :D

I shall just go back to work and let you fellas handle it. :)

Dave Taylor
02-22-2008, 04:25 PM
Does that mean I kin' have Cee Exe's cookies, huh, kin' I? :yipee:

02-22-2008, 04:48 PM
I'll get the oven ready!

So, My bathroom straddles a support wall. From the support wall to the exterior wall(outside support wall) is 13' each way. But from the center support wall that the bathroom straddles to the edge of tile is about 64" one way and 22" the other way. I will be tiling less than 70 sq feet. There is no subfloor currently, just joists(sounds like a good band name-Just Joists).

If only I had a Picture Genie to help me post those photos.

I'll keep trying.


02-22-2008, 04:56 PM
No, that's not what it means, Dave. :mad:

Do tell how those joists are spliced over this center support, Kim. How far do they overlap one another and are they fastened together or just to the support beam?

Your situation is most likely actually worse than if you were tiling an area entirely over one of the 13-foot spans than over that beam. Gonna be a bad place for some upward movement when there is live load on the floors outside that bathroom.

Now I'm really goin' back to work. :)

Don't give none of my cookies to Dave Taylor. :rolleyes:

02-22-2008, 05:05 PM
Kim welcome to the forum.

Here ( is a link to help you post some pitchers. We love pitchers. :)

crow wing
02-22-2008, 05:28 PM
Kim if you dont have alot of wires or duct work I would just sister the joists from the topside (from the bathroom) and move on no need to open the whole can-o-worms. Just my two cents.

02-22-2008, 05:58 PM
Hi Marge, The link loops back to the thread that lists it. Would you have another of getting there? Thanks

As for the sistering-it's not possible from above if, as I understand it, I must support the center 2/3 of each joist. See, the entire second floor has only 3" pine t&g, even under the walls. I can not get to the joists without doing major demo(which I really do enjoy, but my family needs to live somewhere).
The bathroom sits on both sides of a support wall so I would need to tear up from one side of the house to the other.

Can I just beef up joist support in the bathroom only? That is all torn up already.

CX- I get what you are saying about about floor movement when weight is applied to the floor outside of the bathroom. Good point!

The joists cross over the center beam and overlap about 1'. The are nailed to each other at the overlap. They are sitting on the beam, not attached to it.
The area being tiled is about 7 feet wide and the center beam sits in the 22' in from one side.

Pics coming as soon as I figure this uploading out.

Thanks to all.

crow wing
02-22-2008, 06:09 PM
Kim if for example your bathroom were 8 ft long you would nail your 6 ft sister joist 4 nails every 16 inches along length of sister no need to overlap support beam at all. (if I understand you allready tore up the floor you should be looking at the joists???) :shades:

crow wing
02-22-2008, 06:23 PM
Just went back and re read this thread and I think you are saying you have a two by 8 spaning 22 ft :crazy:

02-22-2008, 06:43 PM
She's got two 13-foot spans, Loghead, with a common center support. And no way at all to do any effective sistering. Your proposed six-foot sister just isn't gonna buy her anything.

My opinion; worth price charged.

02-22-2008, 06:48 PM
Thanks Crow Wing,

I am desparately trying to post a picture but...

My old house has a front, center and back wall providing the only support. The joists run 13' overlap at the center and then run another 13'. My 2nd floor bath straddles this center support. I will be tiling a section that will span 7 feet of the joists. This lays 22" on one side of the center beam and 64" on the other side of the center beam.

I didn't understand from the earlier posts if I could 'sister' and beef up the joists just under the bathroom which is currently exposed or if I need to go below to the 1st floor, take out the ceiling and beef up the actual center of the joists. This part of the joist is currently under the rooms on either side of the bath. Not accesible from above due to flooring.

Wow that's a bit confusing I know. Darn newbies huh?

02-22-2008, 07:13 PM
No, not really confusing at all, but a bit unfortunate, for sure. Your only real way to tile that little bathroom successfully would be to sister all the joists on both sides of the beam, and that still only gets you a ceramic tile floor, not the stone you really want.

Unless you can install some walls or beams under the joists on the first floor, of course. Or are willing to install even more sisters. Or willing to install deeper sisters and drop the ceiling below a little. Or...........

They make some really nice looking vinyls these days. :shades:

My opinion; wort price charged.

02-22-2008, 07:30 PM
I know, I know...I can't have tile.

But I was so excited that I figured out how to upload a picture I couldn't resist following through with it.

Thank you CX for the great info!
The hubby will have to learn to love vinyl.
He's not very happy right now though.


02-22-2008, 07:38 PM
We frequently tell folks, "It's your house and your dinero and if you wanna toss the dice and install stone, go for it. Your customer is not likely to sue in the event of a failure."

We also frequently also tell folks that we can't guarantee a failure, we can only tell you what the industry has found to work and that's what we recommend.

But in this case I'll go pretty far out on a limb to tell you that your natural stone installation will fail over that beam. Whether the failure will be ugly enough to make you wish you'd never done it, I cannot say. But it's gonna crack there, by and by.

You wanna put down a couple layers of plywood and some Uber Ditra and prove me wrong, I'm all for it. If it were my floor and I sincerely wanted stone, I'd pewt me some stone. But I'd also pewt a mud bed first. :)

Tell the Tile Ranger I said all that and I tell him y'all lie. :D

My opinion; worth price charged.

02-22-2008, 07:52 PM
He is REFUSING to take no for an answer! His logic...

we removed all the old sheet rock and a thick layer of plaster, a cast tub. That's a lot of weight he says. Switching to a 48" shower stall and drywall, frees up weight that has worked up there for 80+ years. Now we can put in tile right? :blah:


I need an official statement that it is not OK from a man I guess to prove this is not ok.

Could one of you please sign my note...

CX where shall I send your cookies> :)

02-22-2008, 07:54 PM
Darn it your post beat mine and now he really thinks it's ok.

His tail is actually wagging!!!

02-22-2008, 07:58 PM
Oh, it's certainly OK for him to install the stone if he wants to. Doesn't make the installation anywhere close to meeting industry standards, though. :shades:

And tell him his argument fails because he is talking about removing dead load and the deciding factor here is deflection under live loads. They fit inna same basket, but it's still apples and oranges. Weight isn't the issue. :)

My opinion; worth price charged.

crow wing
02-22-2008, 08:00 PM
Life has no garntee glue it screw it down 2 layers use schluter and dont look back ! the picture helps alot.

02-22-2008, 08:02 PM
Weight isn't the issue.

Only if he isn't eating all those cookies Kim appears to like to bake. :D

02-22-2008, 08:08 PM
Marge you must have struck a cord because he finally quit looking over my shoulder and insisting I type more! (hee hee) :clap2:

Thanks to all...we'll see how this goes and check back.

02-22-2008, 09:06 PM
Two layers of plywood, and two layers of Ditra, and cross your fingers and hope...

crow wing
02-22-2008, 09:51 PM
Jim does 2 layers of ditra give more allowance for movement?? Have never tried that.

02-22-2008, 10:42 PM
Schluter did some unpublished testing of double-layer Ditra, Loghead, couple years ago. Was apparently pretty successful. Led to the production of a much taller version of the product, which one of our regulars dubbed Uber Ditra when we were at Schluter school last September. That should be on the market sometime soon and is allegedly gonna be indicated for stone installations over single-layer plywood. Haven't seen any of that in writing, of course. :shades:

But I wouldn't be above doing just what Jim is suggesting there. :)

02-23-2008, 10:09 AM

Since we have moved into the realm of non-standard advice here now (i.e. not to industry standards), there are some things you can do to your joists that will help. The advice others have given in other threads regarding having to sister the middle 2/3 of the span is really only correct when you tile lies somewhere in that same span. In your very particular case (won't work most places), sistering (or some variation of it) can provide some help here -even if it does not lie in the middle 2/3 of the span. I can't tell you how much without digging out some of the old engineering books and doin a lil relarnin, but if you are thinking about going ahead with your non-standard installation, it may help in hedging those bets. What the heck, you already have your floor open, and if you could do the work from the top, why not? If you are nervous about going ahead as-is and end up going the more conservative vinyl route, then this is definitely not worth your time/effort.


02-23-2008, 10:19 AM
I'm still of the opinion that trying to sister the exposed portions of those joists would be a complete waste of time, Casey. Sistering anything that does not include at least the center two thirds of the joist span is not gonna be effective in reducing joist deflection. Sistering five feet at the end of a thirteen foot joist is just not gonna be helpful.

And that's gonna be true no matter on what portion of the joist span the area to be tiled lies. In this case it will be exacerbated by the tile area lying over those joist ends where any deflection near center span will be converted to a lever action over the support beam with substantial mechanical advantage. Not much movement, arguably, but with sufficient force to move whatever's installed above that area.

My opinion; worth price charged.

02-23-2008, 04:53 PM
O.K. So after I turn off my computer last night my tile lovin hubby says lets go test the 'live' load CX explained to us. He had me watch the bathroom floor joists while he jump up and down on the other side of the wall! No movement, so we can tile... :lol1:

He's movin' on. Went to the hardware store and sparked a debate with the information found on this fabulous site. He's feeling confident now that Mr. Yoder told him would be OK.

Now, I talked him into 3/4 plywood. He bought AC because it was on the list of useables. What does the total ply thickness need to be? Do we need another layer? If yes, how thick?

Is Ditra the only product I can double up? We are a bit limited to supplies out here in Amishville? Could any underlayment be doubled? If we do this is it

Am I correct in estimating over 2" when complete?

He has taken over the plumbing and I hid the couplings so I have bought myself sometime!!!

02-23-2008, 05:06 PM
Go over to or search in the liberry here and read the instructions on installing Ditra. It will describe exactly how to prepare the subflooring. It will not say anything about using two layers of Ditra, but will tell you how to install it.

No, I don't think you have a reliable chance of using two layers of something else unless it is a knockoff of Ditra, and even then...not sure. Remember, this is a non-approved install over a substandard structure.

While on Schluter's site, they've got some promotional material that show how DItra protects the tile from movement. Basically, it looks like a waffle. When you fill it in, those towers of thinset hold the tile up, but the frame of the waffle encloses each of those towers. The tile and the thinset can move and the waffle frame can flex without the tile and the towers having to. By putting two layers, you've increased the isolation of the floor from the subfloor. Something like cbu is rigid, so it has no flex to it and can't do the same thing.

You need at least a 3/8" second layer of plywood, more would be better, and glue and anchor that first layer VERY carefully. The addition of glue on the joists will stiffen up the floor as much as possible when anchoring the plywood to it.

IF you go this route, there will be lots of people looking for a long-term update on how things worked out. Well, it could be a short-term disaster report, but that would be useful too. It's your house, you've been advised on the right way to do it, and if you now choose to ignore that...all bets are off - good luck!

Note, there are some industry reports discussing long-term failures. It can take years for the deflection to create a problem as the joists slowly droop more an more under the weight. One report said on that instance, it took 10-years. You could get more, or less, or never see a problem. there are just too many variables, and in your case, by not beefing up the joists, you've exaggerated the biggest one against you.

02-23-2008, 05:25 PM
THANKS A TON!!! I will pass this on to the new fore-MAN. I really apprieciate the time you all have taken to help out. I will check out all the extra info you gave me and get you posted on the 'pass or fail'.

02-23-2008, 06:43 PM
He had me watch the bathroom floor joists while he jump up and down on the other side of the wall! No movement, so we can tile...The movement that is gonna crack your tiles is not something you can see or likely even feel. It's possible you could detect it with a dial indicator if you could get one set up correctly at the end of that joist. :shades:No, I don't think you have a reliable chance of using two layers of something else unless it is a knockoff of Ditra, and even then...not sure.I certainly agree with that. Ditra is unique product among the tiling substrates avialable out there. If you can get holt of the Uber Ditra, I think I'd try it there. If not, you can do the double Ditra if you just want to experiment, but I don't think either is gonna buy you anything more in this situation than just a layer of Ditra. What's most likely to cause a failure in your case is a vertical movement and nothing is gonna save your tiles or grout from that, not even Ditra.

Do all the things Jim (jadnashua) is describing and hope for the best. More plywood is better on that second layer. And then don't worry. If it fails, I'm sure Mr. Yoder (whoever he may be) will come over and replace the whole thing for you, free labor and materials. :D

My opinion; worth price charged.

crow wing
02-23-2008, 07:03 PM
Cx :idea: If cracking along the grout line following the beam is a very high possiability for you use a Schluter expansion joint to match grout color.
My thought is this is not a high risk deal with the schluter Ditra.
OK I am the new guy Ill go lay by my dish :bow:

02-23-2008, 07:08 PM
:) Obi-Wan Kenobi...I mean CX...Thank you! When you say more ply, do you mean more than 5/8 over the 3/4?

He's doing this so we might as well try to make the most of it. I'll hunt down ditra and tell him to quit jumping up and down!!!

02-23-2008, 07:12 PM
one more thought...I think I can just turn this bathroom into a small(very small) skate park. I'll have quite a ramp heading up to the top of all this ply, ditra, thinset and tile huh?

02-23-2008, 10:37 PM
Okay, here's another thought if height is an issue. Screw and glue cleats on both sides of each joist set so if you set 3/4" plywood on them, they will end up being flush with the top of the joists. Cut the plywood so the grain runs between the joists (i.e., across the short side so you'll end up with 4' pieces). Then, put a full sheet across the joists offset as if you had a full sheet down for the subfloor. The full length cleats will help to stiffen the floor a little, and you'll be able to get your second layer of plywood 3/4" lower than if you put both sheets on top.

02-23-2008, 10:53 PM
I would normally agree with Jim's suggestion, but not in this case. The double layers of plywood are the only protection you'll have over that area where the joists ends will move vertically. I wouldn't wanna lose any of that. :shades:

My opinion; worth price charged.

05-14-2008, 08:13 AM
Wow, it took 4 months to get all the walls and fixtures in. Now on to the floor. I am putting Kerdi seams down today and starting with the Ditra tommorrow. I'll put up a picture and post an update on the state of affairs after the installation. Thanks again for all the advice.

02-23-2009, 08:23 AM
Just a quick update. It's been 9 months since finishing floor. Our old support was not rated (using the calculator) for ceramic tile yet my hubby really wanted granite. I thought it was silly to even try. We debated, he won. Over the floor joists we laid tongue & groove sturdifloor...then double layers of ditra...then the granite. As of today there are no cracks. I know they may come...I'll keep posting.

04-20-2012, 06:56 AM
Hello there,
We are approaching approaching the 4 year mark and still no cracks! Thanks again for your help and advice! The combo of sturdifloor and doing double ditra is a winning one (-; Going to try it on a kitchen install this week.
Handy Housemaid

04-20-2012, 10:08 AM
Thanks for the update, Kim. Glad it's working. :)