I can't answer as to the deflection, but if the floor is too bouncy, the tile will come right back up. What size are the joists? I wouldn't just ignore it, tempting as that is: think how awful it will be if all the work and money you put in is wasted, plus you have the mess of taking it out and doing it over.

As to Ditra though: I LOOOOOVE it. It helps prevent cracking, and if you band the seams [or use caulk] you can essentially water-proof the floor. Gives you a chance to address a leak before the structure is damaged.

Lighter than a CBU backer, it goes down much faster and easier. Makes a thinner layer, too. Two downsides: cost, and it kills your knees to kneel on the plastic squares while tiling. I prefer a pad that I toss on the floor over the ones you wear, fwiw.

Only trick to it is that you want a nice wet thinset, just like for the kerdi. Otherwise, the fleece back doesn't get stuck down as it should. The channels in the back let enough water to evaporate that you can use a modified thinset, but you set the tile with unmod, just like the kerdi [Bill taught me that-- thanks again, Bill!]

Actually though, I think I used un-modified front and back the first time I used ditra, and those tiles are still stuck after about 6 years...

My understanding of Ditra (from John Bridge's 'Tile My World' book) is it's primarily used to uncouple the tile from the substrate allowing movement and thereby eliminating cracking and delamination. At least that's the primary reason we used it in our MB and will use it again in our 2nd bath. The waterproofing aspect is nice too.

I give Ditra six thumbs up. WAY easier underlayment to use (fast, no mess from cutting cement board) and the incremental cost is only like $.60/square foot. That's worth a few hours of labor in my mind.

Don't ignore the deflectolator. If you have too much deflection in your floor, your tiles and grout will crack.

PF-- One thing you need to understand about Ditra-- the floor needs to meet deflection requirements BEFORE the Ditra goes down. In addition, for natural stone, you need to have two layers of plywood adding up to atleast 1 1/8" under the Ditra. Anything less and you'll have problems. Next, you say your joists are 16" on center, and 14' long. I'm going to assume your joists are 2x10's, otherwise they wouldn't even meet the minimum L/360 requirement which is needed for almost ANY flooring. Actually, if you used the calculator over at John Bridge's site, it'll tell you even that's shy, that the longest they can be is 13', but with some species of wood, 14' will go. Here's the problem. With natural stone, the deflection requirement is literally TWICE as stiff-- L/720-- and to mee that, the longest 2x10 joists 16" on center can be is about 10 feet. being that you're using a smaller slate, if you were even CLOSE to that, I'd attempt it. But with what you've got, I'd seriously consider a porcelain slate lookalike. Otherwise you're going to have problems, and it won't take too long before you do.

There are a couple of things you can do to rectify the situation. One would be to use a couple of lollicolumns and a beam across the joists at midspan. Of course this would only work in an unfinished basement, and would curtail your use of the space dramatically. Another thing you can do is to sister new joists to the old ones, thereby increasing the strength of your joisting system enough to bring it up to where it needs to be. This can only be done, though, if you don't have alot of electrical, plumbing, etc. going through the joists.

One other thing you didn't say one way or the other-- any chance you have any walls bridging the joists anywhere in that span?

Please clarify about uncoupling? When I used backerboard, it was thinsetted and screwed like heck to the subfloor, how does that allow uncoupling? To me, that seems like "one" chunk of stuff not moving anywhere.

Okay. It may look and FEEL solid. But all materials will move, basically expanding and contracting with the changes of the seasons, as well as changes in humidity. Unfortunately, wood expands and contracts at a much grater rate than tile, which is why cement board is used as a bonding surface. It's moves at a rate much closer to that of the tile. What happens with an uncoupling membrane (Ditra) is that you have the waffled plastic, which the thinset doesn't actually bond to. It "keys" into the dovetailed waffles, pretty much "locking" the thinset in place, once it dries. Underneath, you have a fleece bonded to the underside of the plastic. This is what bonds to the subfloor by way of thinset. If there's ANY movement that would delaminate the tile from the underlayment, the fleece will let go of (uncouple from) the bottom of the plastic, while the plastic sheet holds the tile together.

This is a bit oversimplified, but it's the basic jist of the system.

OK, yes, when I remeasured, they are 13', 2x10's, over the livingroom, so the area to be tiled is as such.

**Bill, thanks for the detailed answer: I assume you mean 2 layers of ply in addition to the subfloor?

We may be able to accommodate that. Yes, I have been considering porcelain tile for this reason, nothing ordered yet... just can't find the same color scheme at all. *&**!! Really not able to buddy up extra joists- all the plumbing is there...

Weedyacres, I love your photos, very inspiring, have used them for tips on little things we have needed to resolve- I like your Ditra pics too.

Thanks oruboris.

Another question- the effect of the Ditra, uncoupling, that doesn't have any direct relation to the deflection, though, right?

Sigh.

Thanks Sarah

So, let me clarify, as I have mulled on this all day at work...
1: the sub floor planks (3/4") additional plyboard (3/8" or even 3/4"?), then Ditra (or CBU backer).
The Ditra acts on the horizontal plane of movement.

2: the deflection >L/360 or >L/720, to determine type of flooring, and this addresses the movement on the vertical plane.

Is that right? (eager student smile)

THANKS!!

I assume you mean 2 layers of ply in addition to the subfloor?

No, the subfloor, plus one more layer.

So, let me clarify, as I have mulled on this all day at work...
1: the sub floor planks (3/4") additional plyboard (3/8" or even 3/4"?), then Ditra (or CBU backer).
The Ditra acts on the horizontal plane of movement.

2: the deflection >L/360 or >L/720, to determine type of flooring, and this addresses the movement on the vertical plane.

Is that right? (eager student smile)

Works for me!!

Cool! Thanks Bill!

Hi,
I am totally new at home repairs. Trying to put down Dita in my small bathroom for ceramic tile.I put down yesterday then pulled back up and scaped the thinset(Tek sturdilight modified thinset) off the floor.I made it like soft butter but the ditra did not sick to the mat, then made some more thinner mixed it in on the floor and tried again, still no thinset on mat. Pulled it up again, clean floor. Then tryed same thinset when I got it so you could pour it out of the container but just held the trowel makes, thinset was on most of the mat. Left it to dry over night and checked sample it pulled of the thinset quite easily. Is this normal, should I have to have the thinset like running pancake batter and not soft butter. I would hate to lay it down and the whole floor come up. Would appreciate any advice. Everyone I know that has down ceramic tile say I should have put on wire mesh. I used ditra as I thought it would be easier and I was told I should not lay the tile just on the 1/2 plywood, 3/4 plank sub floor, 12 joist.

Thanks for you help,

Jackie

Okay-- first of all, what they're suggesting is what's known as "lath and scratch" installation. It was widely used back in the 80's (I've even done a few installations with this method), but it's been found to be the fault of so many failures, that it's now frowned on in the industry. Do a search on its slang name (Jersey mud job)-- you'll see what I mean.

As for the Ditra, yes-- you want the thinset to almost be runny, to make sure it gets into the mesh on the back. The mat should darken in color when you set it. It wouldn't hurt to take a flat trowel, or even a rolling pin, and go over the mat to try and help bed it into the thinset. Also, it's recommended to use a v-notch 3/16" trowel. It's been my experience that the v-notch doesn't put down enough thinset. When I install Ditra, I'll use a 1/4x1/4 square notch, instead. Try those couple of things, and I think you'll have better luck.

Same, I use a 1/4"x1/4" square for Ditra.

I use the recommended V for Kerdi though.

Hi,

Thanks for the suggestions. I will try the 1/4 by1/4 square notch tomorrow.

Jackie

hey jackie - maybe take a small piece of ditra & a scrap piece of wood & test things out before you commit to the floor again. that way you can see the consistency that works & the darkening color of the ditra, etc.

also, this may be a dumb question, but are you sure you are putting the right side of the ditra down? the fleece(soft fuzzy) side should go down into the thinset on the subfloor.

Hi,

Success:)The bigger trowel worked better.

Jackie

Hi,

Now for the tiles.

How thick should the thinset be when laying down the tiles on the ditra. From reading the forum it appears you can fill the ditra first and let it dry, then put another coat of thinset on top and put the tile down or do it all at once. Which is best way(the one most likely to succeed).

I am going to lay out the tiles tonight and get an idea of how they should be layed and cut. I have bought a small wet saw and some nippers to cut the tile with. Is it best to cut the tiles then lay them down or cut them as they you go in case I have to make a change. I do not imagine I am going to be the quickest at cutting the tiles.

Thanks for the help.

Jackie

Both ways will succeed, but you're better off if you fill the waffles and set the tile at the same time. Then the thinset all dries as one unit, rather than having to bond to itself. As for consistancy, I'd say about the way you described your consistancy before when you were having problems with the Ditra.

Use the flat edge of the trowel to apply the thinset to the ditra, filling all the recesses, leaving it a little thick. Work in small area at a time, maybe a 2-tile by 2-tile grid to start with.

Then come back and comb it with the notched edge of the trowel, then set your tiles.

As you get used to the workflow, you can increase your grid.

As for cutting tiles, honestly, if you're cutting them in advance, then you have to hold to those same layout lines as you set the tile. If you start wandering off your grid lines, then your cut tiles become useless.

You can cut as you go, but that does slow your workflow.

Or you can do all the field tiles, then come back the next day and fill in the cuts.

Or you can do a few courses of whole tile, them cut three or four cuts at a time and fill in. Then do the next 3 or 4 courses of whole tile.

Myriad ways to skin this cat.

Much depends on the floor layout and how you work your way across the floor.

Mongo

Hi,

Laid out my tile on the floor and notice that in one corner right by the door I did not put enough thinseton the floor and it is a bit lower and the ditra is not stuck to the floor(about 5inch by 5 inch piece). I think it is only about 1/8 inch lower than the rest of the floor. Since it is in the corner it will not be walked on and the door trim should just it sit on top of part of the tile. The tile that will go in this place will be cut to be 12 by 6 1/2 inches. I can not avoid cutting the tile since I am one inch short on 3 tile that would cover the whole width, theirfore I was cutting the tile to put 6 1/2 inch tile on each side.

At last the question. Do you think it will be OK to just lay down the tile and it will stay down. I hoping the thinset will take up the 1/8 low area. Could I use something like contact cement under the ditra to hold to the thinset already their and hardened

Thanks,

Jackie

If you want to know what you SHOULD do, I think you know that answer already. If you want to know what you can get away with, from what you're saying, it's possible you can do what you suggest and get away with it, especially being that it's not in a traffic area. But if it were me, I'd cut that corner out of the Ditra, and take another piece and reinstall it properly.

Thanks Bill,

I will take your advise and cut the piece out and try again.

Jackie

Hey Bill,

It worked. The new piece is not stuck to the floor.

I hoping the tiling goes better than the ditra.

Jackie

Hi Again,

I am ready to start putting the tiles down. My bathroom is quite small, 5 by 7ft. .I tried to leave perimeter expansion joint of 1/4 but in some place it is only 1/8 inch, this is mostly due to the fact the ditra went over the plywood a little bit.I did leave 2 expansion joints in plywood floor itself Can I get by with 1/8 since it is such a small area or must if cut back the ditra and in a few places the plywood to 1/4 inches.

Jackie

Get out the micrometer and.....

Just kidding-- you're fine. :-)

Hi,

The tiles are now down and I think it looks pretty good for my first time. I use a small wet saw and it cut very well. Have only 2 tiles left(I had a few cutting mistakes), should I buy a few more tiles just in case they break.

Now for grouting and chalking. Is it best to do the chalking around perimeter joints first so I do not get any grout in them or grout first then chalk.

My space between the tiles is 1/8 inch and I have bought sanded Tec colour grout(polymer enhanced portland cement) and the matching colour sanded siliconized acrylic latex caulk. If this is not correct I can take it back and change it for the right product.

I have read that I should keep the grout moistened but the directions do not mention to do this. Also the direction say wait 1/2 to an hour before cleaning the grout of the tile with sponge but at the store they told to me wipe it with very barely wet sponge right away.

Any grouting tips would be greatly appreciated.

Jackie

should I buy a few more tiles just in case they break.

You can if you like, but if everything was done properly, it shouldn't be necessary.

Is it best to do the chalking around perimeter joints first so I do not get any grout in them or grout first then chalk.

I'll usually grout first, making sure not to fill that joint, and then caulk. The reason is that if you grout afterward, you'll end up with spots of grout on top of the caulking. Grouting first just makes it easier to do a nice clean looking job.

My space between the tiles is 1/8 inch and I have bought sanded Tec colour grout(polymer enhanced portland cement) and the matching colour sanded siliconized acrylic latex caulk. If this is not correct I can take it back and change it for the right product.

You got the right stuff.

You wait that long, and you'll be cleaning the excess grout with a jackhammer! Don't try and grout the whole area at one time. Go only as far as you can before you see the grout starting to haze up, and then go back and begin to wash what you have. As for the barely wet sponge, they're right, but just so that you understand, that means dunking the sponge and then wringing it out as well as you can.

As for grouting tips, I have two. When you first start washing each area, wash in circular motions to loosen up the excess grout on the face of the tile, and "shape" the joints. Once you've done that, rinse the sponge out well, and take two swipes diagonally across the tiles-- one with one side, and one with the other, both in the exact same place. The first swipe will remove the heavy grout, and the second, you make with pretty much just fingertip pressure, so the sponge doesn't hit the joints any more than necessary, and that one should clean the tile pretty well. Then rinse the sponge out and move on. Once you're done with the area, you can get a clean pail of water, and go back and give it a final rinse, and when you're done the few minor streaks that are left should come up easily with a mop and water. If you see any HEAVY streaking while washing, though, don't be afraid to hit with the sponge again, but remember-- the big key is one swipe per side of the sponge before rinsing.

Hi,

Tiled and caulked the floor and it looks fine.

Now I need to deal with the bathroom floor being 1/2 higher than the hallway. I pick a a metal door trim that is suppose to equalize the floors but I would have to drill holes in the time and I am afraid they might crack. Any other suggestions and if not what is the best way to drive a hole in the ceramic tile.

Thanks again,

Jackie

How about a marble threshold with what's called a "hollywood" or "handicapped" bevel on one side? (basically looks like a ramp from one edge about 1/8" thick to the full thickness of about 5/8"- 3/4" in the center)

Check the following site, a little ways down the page-- it illustrates it alot better than I describe it!

Here is a link that might be useful: thewindowsills.com

We ended up with 5/4" (yes, 1 1/4"!!) difference in the floor height due to leveling up the bathroom floor. We got a marble sill with the "hollywood" profile just as Bill mentioned- it's like one long wide bevel. Stepping onto it is great and doesn't seem like I will ever stub or notice the height change!

Looks great too.

Hi! I want to make 1/4" ceramic wall tiles thicker to match adjoining 3/8" tiled walls. Can I use 1/8" Ditra (cut to size of 1/4" tile? Or, how else might I increase the thickness of the narrower tiles? Thank you