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kevreh
10-15-2002, 10:48 AM
Hi all-

First, big thanks out to the moderators and members who make this forum soooooo helpfull.

Few questions about my new tile job. The info:
- Laying 16" sq. porcelin tiles with 1/8" gap
- 13' x 22' living room
- existing 1/2" particle subfloor
- trusses are 16" oc and made from 2"x4" (see below), they run the length of the room
- adding 5/8" plywood sheets (4x8'), with liquid nails as an adhesive along with screws.

Trusses, side view:
====================
/\/\/\/\/\/\/\/\/\/\
====================

We want to do a good job, but won't be in the house for more than 5 years, so I'm not obsessed with longevity. We know about ditra, but it would be a budget killer.

Does this sound ok/fine?

Not looking for a hack approach but not the Mercedes approach either. I hope I'm on the right track since I layed down half the 5/8" sheets already

thanks!
kevin

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Bud Cline
10-15-2002, 11:16 AM
If the 5/8 sheets you've layed down already are particle board then your off to the worst start possible. I think your saying they are plywood though, right? The tile isn't likely to stay down five weeks much less five years on particle board.

If it's plywood, then this is being done but it also isn't the recommended method, at least not here. The plywood is necessary to cover the particle board but you will also need some type of tile backer, 1/4" cement board for example. The cement board is installed with a bed of thinset and screws or nails.

Are you shure about the 2" X 4"s, and the direction they are running? Can't be!!!

If you seriously want some help here then stop and let's talk about this.

bbcamp
10-15-2002, 11:26 AM
You didn't mention backer board. Good thing, 'cause the Tile Council doesn't recommend CBUs over trusses, no matter the underlayment (Tests will be conducted, but you'll probably move before they're finished!). That leaves Ditra on 5/8" plywood as the underlayment.

Your trusses run the long direction of the room (22 feet)? Do you have any information about them (how deep, how far are the cross braces spaced, is the top 2x4 mounted narrow side up)? The floor deflection must be less than L/360 for tile to survive.

Since you are not going to stay, why not install a good vinyl floor covering, instead?

kevreh
10-15-2002, 11:56 AM
Some follow up:

- Its 5/8 plywood, not chipboard
- I though cement board or Hardibacker is only necessary for wet installs. Didn't consider cement board, Byrne doesn't mention this in his book. How does this match to bbcamps message?
- My best description of the trusses (from memory): The 2x4's are flat (or wide) side facing up. The angled 2x4's are at a 45 degree and and zig zag, like my ascii illustration. Check out this picture, they're like the ones on the right: http://www.cnr.vt.edu/dendro/forsite/tb2.htm and this site (small image in upper right): http://www.ufpi.com/market/oj/specifier/info_spe/index.htm

Yes, they run the Long direction of the room, so each truss is 22' long.

-So using L/360, I get ".06". What do I do with this number?

bbcamp
10-15-2002, 04:01 PM
Here's the bad news: the trusses were not designed for a tile floor. The top chord (the 2x4 running across the top) is laid weak side up. This means that the local deflection will be higher than tile can stand, and it, or the grout, will break. The cement backer board people have tested this and it doesn't work. The Schluter people have tested their method, and they stand by it. You are doing the right thing with the additional 5/8" plywood, if you are going with the Ditra.

The L/360 thing is for the engineer (me) to compare the deflection of your trusses under the load of daily living (live load). So, I need to know how deep the trusses are. Measure from top to bottom. If the calculated deflection is less than the L/360, then buy some Ditra, and go to work. If not, buy some wood, vinyl or carpet.

John Bridge
10-15-2002, 04:44 PM
Kevreh,

You might consider contacting a Schluter rep. You ARE saying that the top 2x4 chord of the truss is laying flat and not on edge?

http://www.schluter.com

kevreh
10-15-2002, 06:01 PM
Originally posted by John Bridge
Kevreh,

You might consider contacting a Schluter rep. You ARE saying that the top 2x4 chord of the truss is laying flat and not on edge?

http://www.schluter.com

Yes, they're laying flat... not on edge. Same for the botton part of the truss. It won't hurt to call them, but aren't they pretty much going to say that I should buy their product "just to be safe"?

Don't get me wrong, I'm all for doing a good job (probably not the best job though). I'm just trying to figure out how much this is worth the extra $500 its going to cost.

kevin

kevreh
10-15-2002, 06:04 PM
Originally posted by bbcamp
Here's the bad news: the trusses were not designed for a tile floor. The top chord (the 2x4 running across the top) is laid weak side up. This means that the local deflection will be higher than tile can stand, and it, or the grout, will break. The cement backer board people have tested this and it doesn't work. The Schluter people have tested their method, and they stand by it. You are doing the right thing with the additional 5/8" plywood, if you are going with the Ditra.

The L/360 thing is for the engineer (me) to compare the deflection of your trusses under the load of daily living (live load). So, I need to know how deep the trusses are. Measure from top to bottom. If the calculated deflection is less than the L/360, then buy some Ditra, and go to work. If not, buy some wood, vinyl or carpet.

I measured the trusses.... they're actually 19" oc and are 14" high, from top of upper 2x4 to bottom of lower 2x4. So, whats the calc you would do?

thanks.....
kevin

kevreh
10-15-2002, 06:07 PM
By the way.... is there anything more affordable than the Ditra?

There's no turning back... we've already ordered the tiles and my wife and I have our heart set on them.



kevin

bbcamp
10-16-2002, 05:50 AM
I looked up the trusses on the Alpine Engineered Products website (not to say that they made your trusses) and their tables say your trusses are good for the 22 foot span, with a deflection of L/480 under 40 PSF live/55 PSF total load and a maximum span of 22.75 feet. I also checked the length/depth ratio (in your case 18.86) and compared that to the recommendation for firm (non-springy) floors, which is 18. Lower ratio is better, so you can see your floor is on the edge of being "springy." Adding the extra plywood ("double wood")will help by adding mass and stiffness.

All that means is that if you intend on going through with this installation, go ahead. But buy and install the Ditra!


There is another company coming out with a Ditra-like product, but the cost will be about the same.

tileguytodd
10-16-2002, 06:24 AM
Throw out the idea of using an 1/8" Grout Line.Once you recieve your tile ,measure each one in both directions.You will see that they vary.if you try to use a 1/8" grout line you will have huge trouble.

kevreh
10-16-2002, 10:07 AM
Thanks bbcamp (and everyone). Guess this thread is starting to sound like one started by mace.

John-

I was browsing the archives at the InfoTile website. Seems like there were a few posts a year or two ago where you recomended cement backer board over the plywood. No mention of Ditra. The concensus at the time was that cbu doesn't provide rigidity but also doesn't flex as a result of temp and humidity like plywood. As a lower cost alternative to Ditra could I do the CBU thing?

kevin

[Edited by kevreh on 10-16-2002 at 12:37 PM]

bbcamp
10-16-2002, 11:35 AM
Kevin -

No CBU manufacturer is going to recommend CBU over your trusses on 19" centers. They tried it, and it didn't work.

I did check out the Laticrete website for their recommendations. They will accept the second layer of plywood as underlayment for a direct tile application, if the room does not see "excessive moisture or humidity, such as steam rooms, showers, pools, fountains, over damp basements, or for exterior installations." (Is your living room over an unfinished basement?) The only drawback is that the subfloor plywood (the existing plywood) should be 23/32" to 3/4". Yours is 5/8". At best, you might be able to install 3/4" underlayment to meet their minimum thickness.


If you go with the Laticrete system, be absolutely sure that you follow their instructions to the letter, and use only their products. That way, when you need help, there can be no finger-pointing.

tileguytodd
10-16-2002, 01:56 PM
Keep in Mind,The laticrete system calls for epoxy grout.Its spendy,its tough to work with and it'll drive ya nuts!!

But thier Flexfloor system will work on almost any floor with movement.Ive seen a display built on 3/8" Plywood with 2x2's just on the ends.I can jump up and down on it flexing that 3' section all the way to the floor and not pop a tile or crack a grout line.thats 1 1/2" Of Flex over 3' Dont try this at home Kids :D

John Bridge
10-16-2002, 04:25 PM
Kevin,

Those old posts of mine you found at InfoTile were before the folks at Schluter Systems and Mr. Dave Gobis dragged me kicking and screaming over to South Carolina and "Schluterized" me. Now I'm a convert, and you know how converts are. :D

You won't save a lot on backer board, anyway. You'll still need to bed it in thin set. You'll have to tape it, and the tape is expensive. And all the nailing, man. Plus you'll increase the height of your floor even more.

http://johnbridge.com/schluter11.jpg

Sue20
10-16-2002, 04:52 PM
I don't know "nuthin" about what you guys are talking about on this thread, but I just HAD to comment on the great group shot, looks like you had fun, John!!! Sorry for interrupting the lesson in Ditra, Laticrete, Flexifloors, etc. Carry on......

John Bridge
10-16-2002, 04:55 PM
Sue,


Don't forget to enter the drawing for the tile saw. We'll make a mechanic out of you yet. :D

Sue20
10-16-2002, 05:11 PM
The onliest thing I can draw is "beer"....seriously, though, I appreciate your including me, even though, if I won it, I'd have to pass it on to the next lucky winner.....

kevreh
10-22-2002, 07:56 PM
Thanks everyone for your help. I ended up going with de Schluter. Got it for a good price- $355 a roll (322 sf).

Now I'm just trying to save my back and drill from mixing all the mortar.

:)

kevin

John Bridge
10-23-2002, 05:38 PM
Kevin,

That IS a good price for the product. I think I pay that much. I'm callin' Schluter soon as I get off this board. :D