# wonderboard over floorboards ?



## Diamond D. (Nov 12, 2009)

hi guys, what are your fellings on thinseting cbu, wonderboard directly to 3/4 x 4" floorboards. or should i put down plywood first ,then carry on as usual. the largest tile will be 20 x 20. there is a bit of a height issue though, 2 rooms with 3/8 hardwood,the front door & threshold & a hallway with carpet, well no worries there. anyway, any thoughts on Ditra, what are its limitations, pros & cons etc. i have never used the stuff. all input would be greatly appreciated, thanks.


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## rselectric1 (Sep 20, 2009)

Screen name "Angus 242" will undoubtedly chime in on this question. Listen to him-he's really knowlegeable about questions like this.:thumbsup:


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## Splinter (Apr 5, 2005)

Are you talking about a plank Subfloor, or a T&G finished floor... Either way, you shouldnt apply cement board over dimensional lumber... However, if it's a finished floor you're referring to, remove it to gain needed height. 

Double check the span of the joists to make sure you're alright for deflection requirements and then 1/2" ply and Ditra would give you the thinnest suitable surface to tile over.


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## charimon (Nov 24, 2008)

Let me see you are saying that the subfloor is 1x4" . Laid on the diagonal?? are they t&g?
your goal is Ridgity So if it is an older home...assuming it is based on the subfloor. are the floors sound no saging or bounce.

If it is as above I would glue-n-screw 1/2" ply then thinset and dens. then lay tile. if not then fix the structure first.
Craig


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## Diamond D. (Nov 12, 2009)

it is t&g subfloor boards,but not on the diagonal. i already picked up the 3/8 hardwood flooring.this is a foyer, so the steps ars there, joist span just over 6' and a hallway next to that, span 16', 2 bays one has two sets of x bridging the other has duct work the entire length.but it feels ok deflection wise. i dont have the weights to test it like the loneframer did fri. night, but i will get someone to jump on it while i watch in the cellar, tommorow.

alex , how is that Ditra, do you like.

craig, what is dens ?

PS i'm not doing the entire hallway just 7' 8" to an opening, not that, that really matters, its still a 16' span.


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## angus242 (Oct 20, 2007)

Diamond D. said:


> directly to 3/4 x 4" floorboards


Me is confused :blink:

What are "_3/4 x 4" floorboards?_"

Subfloor = what is laid directly on the joists
Underlayment = what is install over the subfloor BEFORE you tile

You need something over the subfloor _before_ tiling. What that is will depend on a) what the joist setup is and b) what kind of tile you're installing.

Dens. = Denshield (I assume)
Ditra = THE CHITE!!!! I use it for every floor

Proper deflection is not determined by someone jumping on the floor and someone else watching from below. You need to know:
*joist size
*joist spacing
*unsupported span
*joist species
Those answers will get you a proper deflection ratio


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## Diamond D. (Nov 12, 2009)

angus, the subfloor is the 1 x 4 t & g. i guess it was confusing when i said 3/4 x 4. the underlayment is TBD, cbu, Ditra, only on subfloor or plywood first then cbu or ditra then tile ? thats what i'm trying to figure out. the tile, 20 x20 & 13 x13 cermic. i was just kidding about jumping on the floor. but the 2 x 10's are spaced 16 oc and the span detail is above. 6'+ tripled up for stair opening & 16' with bridging.the species? its not a stone so i have no idea, possibly hemfur ? house built in 1950's maybe yellow pine. hope that helps.... SO you LIKE the Ditra, A. thanks for your help. D.


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## angus242 (Oct 20, 2007)

Diamond D. said:


> angus, the subfloor is the 1 x 4 t & g. i guess it was confusing when i said 3/4 x 4. the underlayment is TBD, cbu, Ditra, only on subfloor or plywood first then cbu or ditra then tile ? thats what i'm trying to figure out. the tile, 20 x20 & 13 x13 cermic. i was just kidding about jumping on the floor. but the 2 x 10's are spaced 16 oc and the span detail is above. 6'+ tripled up for stair opening & 16' with bridging.the species? its not a stone so i have no idea, possibly hemfur ? house built in 1950's maybe yellow pine. hope that helps.... SO you LIKE the Ditra, A. thanks for your help. D.


16' span with 2x10 is pooh pooh. That needs to be addressed before any tiling happens. Can you sister on the outer sides of the bay with the mechanicals? Your deflection ratio is currently around L/270 :thumbdown

Once the joists are supported better, this is what I'd do:
Make sure the 1x4s are all screwed to the joists well.
Add a layer of 5/8" EGP screwed to the 1x4, NOT the joists.
Modified thinset
Ditra
Non modified thinset
Tile

You might get away with 1/2" EGP but I'd prefer 5/8".


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## Diamond D. (Nov 12, 2009)

angus242 said:


> 16' span with 2x10 is pooh pooh. That needs to be addressed before any tiling happens. Can you sister on the outer sides of the bay with the mechanicals? Your deflection ratio is currently around L/270 :thumbdown
> 
> Once the joists are supported better, this is what I'd do:
> Make sure the 1x4s are all screwed to the joists well.
> ...


angus, unfotunatly the vent prohibits me getting a sister in that bay and the next bay over contains the return, however that is under the hall wall if that makes a difference. the other bay is next to the steps ,that side is doubled for stairs then a third about3/4 "away from that, no blocking. the otherside i can remove bridging and probably sneak in a sister, however the joist on the other side of the beam is there leaving me no bearing . i could put a spacer, a 2 x4 top & bottom on that joist then add another 2 x 10 x 16' if that is copacetic. if not i suppose i can add a small beam & posts right on across the 2 bays & be done with it. 

got to do it right the first time, i'll use the 5/8, it will just make it under the door. is the thin Ditra ok. i'll deal with the ramps into the other rooms. i just hope they don't make me put up railings :laughing:

Thanks D.


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## angus242 (Oct 20, 2007)

Diamond D. said:


> angus, unfotunatly the vent prohibits me getting a sister in that bay and the next bay over contains the return, however that is under the hall wall if that makes a difference. the other bay is next to the steps ,that side is doubled for stairs then a third about3/4 "away from that, no blocking. the otherside i can remove bridging and probably sneak in a sister, however the joist on the other side of the beam is there leaving me no bearing . i could put a spacer, a 2 x4 top & bottom on that joist then add another 2 x 10 x 16' if that is copacetic. if not i suppose i can add a small beam & posts right on across the 2 bays & be done with it.
> 
> got to do it right the first time, i'll use the 5/8, it will just make it under the door. is the thin Ditra ok. i'll deal with the ramps into the other rooms. i just hope they don't make me put up railings :laughing:
> 
> Thanks D.



DD, I'll be honest, I'm not understanding how the joists are configured at your site. If you could post a pic you'd probably get a lot more replies about how to shore things up. That's what you really need to focus on. 

If you could get L/360 or a bit better, you could skate by with 1/2" EGP. I'd definitely use the Ditra.


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## Diamond D. (Nov 12, 2009)

angus242 said:


> DD, I'll be honest, I'm not understanding how the joists are configured at your site. If you could post a pic you'd probably get a lot more replies about how to shore things up. That's what you really need to focus on.
> 
> If you could get L/360 or a bit better, you could skate by with 1/2" EGP. I'd definitely use the Ditra.


unfortunitly i don't have the tools to do pic's or even sketches on this new fangled thing,i'm just a beginer. the wife has a picture phone but i probably need a wire to plug into this thing, if i even knew how to do it. anyway let me try to lay it out. walk in door,foyer 80" wide wall on right with opening to room.against that wall and looking straight ahead is the staircace, going up, with cellar stairs under. looking through subfloor joist run front to back, from door to stairs 6' 6" then they are boxed out for cellar stairs. stilllooking at stairs and through the floor, double joist on right under that wall,with another one next to that about 3/4" to the right, this one is just to keep the 16 oc going. the same thing occurs on the other side of stair opening, the double then one to the left, an inch away,between these doubles it is headed off for stairs with 2 joist about 6'6" long. now, next to the stairs is the 16' deep hallway into another room and the cellar door,this is where a main beam goes the width of the house, right to left, that the floor joist sit on. (note: behind this beam is the main air return ) so,next to the stairs is the open bay (save, some electric wires i can move) with the bridging, your still at the door,BTW. where this joist sits on the beam the back joist is overlaped inside this bay by quite a bit. thats where i was talking about the 2x4's for spacing, then the sister. next bay to the left holds the heat duct & can't be moved. and the next bay holds the air return. i hope this makes sence. :yawn: yeah, a picture is worth a thousand words.
. the more i think about it i think the beam is probaly the way to go. either across the 2 16' bays or if you think the doubles by the stairs is to weak. a 4x4 all the way acrossthe 80+" with a post on either side of the bottom step and one at the end under return. just watch your :cursing: head going down the steps. thanks D. gotta go watch the meators!


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## JazMan (Feb 16, 2007)

That was a good explanation, problem is I think only you understand it. :whistling

Back to that 16' span you spoke about. Are you sure the unsupported span of those joists is really 16'? I can't believe it. :no: It would also help if you could figure out the species and grade of the joists too. All wood is NOT created equally you know.

I recommend Ditra too. And. when you install the underlayment do NOT glue it, just fasten to the subfloor. 

Jaz


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## Diamond D. (Nov 12, 2009)

JazMan said:


> That was a good explanation, problem is I think only you understand it. :whistling
> 
> Back to that 16' span you spoke about. Are you sure the unsupported span of those joists is really 16'? I can't believe it. :no: It would also help if you could figure out the species and grade of the joists too. All wood is NOT created equally you know.
> 
> ...


 
hey Jaz, yeah, i thought that might be the case. i really strained my eyes looking through that floor last night for that description too. i will ask Santa, for a scanner or a digital cam. and the wire to go with it. i've been good 

all right the span is only 15' 11" from the block wall, 5" of bering to the 4.5" beam where there is full bering and more. the joist is 17' long total.
it took me a minute, but the joist's are construction grade, west coast hemlock. :detective: Thanks, D.


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## JazMan (Feb 16, 2007)

West coast Hemlock, construction is not in my span chart. Maybe you can find an association or your local building department may know. Ask them you need L360 or better at 50 lb live, and 20 lb. dead weight. L360 is the worst it should be. ie. L 300 is not good, L450 is better, etc. 

Generally SYP, Southern Yellow Pine yields the best ratings. Here's what I got. SYP - #2 - 50/20 to meet L360 - max span 13' 7". Change to #1 - 15' 1". Change to Dense Select Structural - 16' 1".

Please remember that building codes only require L360 at 40/10. That can work for tiles but it is very marginal since the dead weight of the subfloor, underlayment, tiles, mortar and grout is likely to be well over 20 lb. I would never guarantee a floor like that.

Jaz


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## Diamond D. (Nov 12, 2009)

thanks jaz, WCH, too was not specified in my book, only "western woods" and that allowed 13' i think 4" for 360L at 16"oc. so with all the mechanicales,to deaL with, and i have the room, i will just put in the beam. 80" long, a 4x4 with 3 posts. at about 6' from the front, roughly where the stairs start. that leaves 10' or less down the hall where there is only about 18" of tile.i think i have the floor beefed up enough with that. so what is the min. underlayment you would use there, with wonderboard or with Ditra. is the demontional sub floor that unstable that you can't use 1/2 " cbu. is it stabalization i'm after with the underlayment or rigidity with deflection. Thanks for your help. D.


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## JazMan (Feb 16, 2007)

Once the joists' deflection is improved as you plan, you can add min. 1/2" underlayment grade ply, C/C or better, B/C is easy to find. Thicker is better if you can. Then you're ready for Ditra and tiles.

You want the floor to be as stiff as possible, especially the in-between the joists deflection. Ditra and most CBU's can go over 5/8" ply subfloor. But that scares the heck out of me!:w00t: A well properly installed 3/4" subfloor sheet is enough though, with ceramic or porcelain anyway. 

Jaz


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