Now that I am deep into tiling my kitchen floor (12x12 brazillian slate) I start reading about expansion joints and feel a chill. I've tried to keep about 1/4" around the walls free, and my cement board is spaced about 3/16" apart, then mudded/taped. Longest distance in kitchen is about 16 feet. I wouldn't know what an expansion joint was if it bit me. Do I need one? At thresh holds? What do they look like (in terms of construction)? My CB is screwed onto linoleum, without any thinset hodling it down. We have had take-out for dinner for a week, with weeks more to go, seems like: my husband is about to divorce me.

Forgive me if this is so basic. I looked through old threads but couldn't quite figure out what I needed. The tile books don't seem to address this topic, or mention it in such breezy terms it's useless.

Thanks in advance. You guys are very patient with us DIYers!

First off your CBU should have been set in thinset as per the manufactures installation guideline.

General guide for movement joints is to place one at 16' to 20' in each direction.
For a floor that is exposed to a lot of direct sunlight or heated 12' to 16'

The joint can be as simple as filling the grout joint with a colour matched caulk or use a mechanical expansion joint from Schluter

Yes, I am starting to see from this site that I should have used thinset under the cement board. Unfortunately, the helpful people at the tile store neglected to mention that when I asked, and the cement board didn't come with readable instructions... By the time I'm done with my project I might know what I'm doing.

Should the expansion joint line up with cement board gap? Or line up with anything else? My tiles are set on the diagonal. Can the joint just run along with the diagnoal? Thanks so much.

Because your room is fairly small you don't need expansion joints in the tilework. Make sure to maintain a gap from any solid object around the perimeter tho.

As for no thinset under the backerboard....this is not good! And it's on top of linoleum you say? Are you sure you're not a man? We are the ones that often do the work...THEN read the instructions!

I agree with you that those nice people that took your $$$ should have had instruction sheets so you could get satisfactory results. After all, they are selling at retail prices to DIYers that may not know how to do the install properlly? When I used to work retail, I would go into detail from the prep to the cleanup. Maybe the place you bought the materials don't know either? (Was it a big-box store)? In the end tho..it's your resposibility to know how to do it the right way. FYI every manufacturer has instructions on paper and on their website.

This is what might happen because of the way your floor is being installed. You may have a few grout cracks either right away or prob. within a few seasons? (They may not be very noticable at first)? Later grout is likely to show cracks esp. in high traffic areas. The situation may be worse if you didn't use enough fasteners and if that sheet vinyl has any cushion to it. No point in talking about the subfloor requirement of L720 deflection for slate vs. L360 for ceramic tile at this point?

Because slate is soft and porous, be sure to apply multiple coats of a good quality sealer after the final cleanup and cure.

Jaz

Thanks for the info. It feels awful to work on this job now, knwoing that I'm not doing it right, despite my best efforts. There's no way I can change horses now, because half the floor would be 1/4" higher.

Well, as I say, by the time I'm done, maybe I'll know wht I'm doing. And yes, I'll seal the heck out of it with the astoundingly expensive sealer.

The more tiling I do, the more I respect what you pros do. And I sure appreciate how you guys dispense thoughtful advice, and don't rub my nose in my mistakes TOO much!

1/4" higher ? Does this mean you have already started to lay the slate?

Jaz's point about the slate install and deflection issue should not be taken lightly.

I dare say you will be looking at a very expensive repair down the road if the problems are not fixed now.

No one here would do that .... but we have to speak up now so that if you continue on with what you're doing, at least you'll know what to expect in the very near future.
We can't emphasize enough the need to understand how products should be installed and how they relate to the required needs of the tile installation.
I hope you have good luck with the floor.

fair enough.

I have two layers of 5/8" plywood on 9.5 x 1.5 joists spaced 16 on center, with a span of 15 feet. They are braced with criss-cross braces ever 6 feet.

I can't seem to find the actual deflectometer tool on John Bridge's site, though I do find many referencs to it.

I might go and shoot myself. Or have a stiff drink.

The stiff drink sounds like a much better resolve.


Two layers of 5/8" plywood is an asset and the
cross bridge braces are good, but solid blocking is even better ... especially with a 15' span.
Unfortunately none of this is enough for a natural stone installation.

The biggest problem is with the installation of the cement board. If there are even the slightest voids under the cement boards (which the mortar is meant to fill) your tile will suffer deflection because of the cement board's movement.

I don't know why some salespeople can't step up and offer essential information when they should know it damn well matters.

Thanks guys! It's a very fine line between telling people the RIGHT way to do things and rubbing their noses in their work a little. You may know how many times I've been tempted.......? But that is not the purpose of this fine forum. If it were, we'd be better off not responding at all. I could find other things to do, I think?

For others peeking in now, I recommend doing a little research and asking questions before you give some store your $$$. Also don't buy from any store that is not willing to hire anyone that can offer good advice. Even if their price is a little less than the tile pros down the street. Otherwise you're asking for trouble. You are not buying screws or light bulbs, successfully completing a tile project can be a difficult process for many DIYers, AND it's important to do it so it'll last.

Snapdragon, I don't understand what you mean by 1/4" higher? Since you've started the install, just continue of course, and hope for the best. (Unless you can easily start over). When the grout does crack it WON'T be the end of the world.

Are the joists expossed from underneath? Maybe you can sister the joists? Forget the deflecto-meter, your subfloor is fine for tile but not stone, the problem is also the vinyl and no thinset under the cement board.

I vote for the drink! Have a Black Russian for me!

Jaz