marble on bath floor [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-25-2003, 06:49 PM
i have 3/4 plywood and another1/2 glued and screwed.i might go with marble on the floor. i see that alot of the guys here use cbu. i usaually put tile down on the plywood. i saw the big blow out in the pro section. i just wanted to know what type of 1/4 inch cbu i can use and will it be ok for marble. i have to meet a 3/4 hardwood floor and im already 1/4 over without a cbu. i hear marble is soft and i dont want any cracks. any info and opinions will be appreciated

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01-25-2003, 07:24 PM
Hi rancher,
First thing is to determine if your floor joists are up to snuff for marble. The floor has to be pretty stiff for it. Try the Deflectolator ( to see what kind of info you need. Cut and paste the results here to let the engineering staff have a look to see if anything else need to be looked at. :)

01-25-2003, 07:33 PM
i havea slight problem with the calculator. i have 2x10 sistered to 2x6. does that help and what about the span. is that the size of the bath or the span with out any bearing wall under the joist. i have a bearing wall 5 feet from the exterior wall and my bath is 12 feet long

01-25-2003, 08:46 PM
Ah, this is why we have an engineer on staff to handle the tricky stuff. We'll have to get Bob (bbcamp) in here for a look. He will need the length of the joists between supports, as well as the "on center" distance. :)

01-25-2003, 09:37 PM
If you are using green or white marble I would think about use epoxy adhesives. Dont want the tile to curl or delaminate on you.

01-26-2003, 07:46 AM
the total span of 2x10 is18 feet. this from the exterior wall to a micrco lam beam. my 2nd floor bath is 12 feet long starting from the exterior wall toward the micro lam. under the second floor bath is another bath5'6" wide. so my new bath has a supporting wall almost in the center of the second floor bath. then the 2x10 span to the microlamwhich is 12 feet. 6 feet of the 12 feet bath is on this span and then a walk in closet wich will get carpet. i have 2x4 blocking at 9 feet on the span, this is a second story addition, so i also have the existing 2x6 sistered to the 2x10. the 2x6 is on the bottom half of the 2x10 and the spacing is 16 inches . i have 3/4 t&g glued and srewed.and i added a 1/2 sub on top in the bath.i hope this can help the engineer.

01-26-2003, 08:05 AM
I'll shoot Bob an email and see if he can have a peek at this. :)

01-26-2003, 08:40 AM
I dont see any way a stone product is going to get by on this job. Its the 18' span that really hurts. If there were some way to put supports or a beam in underneath and cut that span down.Perhaps.
Bob of course would be able to give you more exacting detail but running the numbers several differant ways comes up the same.No Natural Stone!!!Perhaps you could take a look at a ceramic tile for backup just in case Bob tells you the same. Or perhaps find a way to cut that span down.

01-26-2003, 10:41 AM
If I understand everything right, the 2x10 plus 2x6 joists are are 18 feet overall, and are supported by a wall on the lower floor at about 6 feet from one end. Assuming that the lower wall (bathroom) is a load bearing wall, the longest unsupported span is 12 feet. If the joists are #2 or better Douglas Fir or Southern Yellow Pine, your floor is just OK. L/720 is .2, your floor is .198. Note that this is marginal at best, but does meet the minimums.

So, before you continue with your stone installation, you need to verify what your joists really are (look for a grade stamp) and that the bathroom wall is load bearing (look in the basement for a beam and piers directly under that wall. If either of these two aren't right, stone is a no-go for your new bathroom.

If the lower bathroom wall is not load bearing, the upstairs bath floor is not suitable for ceramic tile, no matter what grade lumber is used. We probably can do something about that, depending on what's in the basement.


01-26-2003, 11:23 AM
i have a 4x10 beam with lolly columns supporting the floor below the lower bath wall. it is not directly under the bath wall it is centered in the baesment for the span of the lower floor.which is about 3 feet from the bearing wall. the joist are #2 df .this was all previously designed by the architect before the second floor was put up.this marble looks like a terrazo floor it has other stone colors in it. the floor feels strong and i only started doubting it when i read things on this forum. it is very informative, iwas also wondering if the ditra would help or hinder.i am old school no movement and your good to go.i saw the movie from ditra and thay show latteral movement on the floor. how can a floor not crack with this movement.

01-26-2003, 01:16 PM
Old school, no movement is only as strong as the tile itself. This direct bond system has been proven with the use of Laticrete 317 mixed w/ Laticrete 333 and their Sp100 epoxies. The finished product will handle tremendous loads (compression and tensile stress) until it breaks through the tile not the grout joints.

The Ditra is an uncoupling system that removes the tile from the sheer plane. The tile is not directly bonded to the substrate allowing for different rates of expansion and contraction b/n dissimilar materials. The dovetails in the Ditra are basically shock absorbers and weight diffusers allowing heavy load traffic and movement b/n the grid joints. The upper side of the Ditra when filled w/ dry set mortar creates a mech. bond in a vertical fashion allowing for horizontal movements throughout the floor.

Ditra can have failures! For example, if an installer completes a job using Ditra and doesn't concern himself with the 1/8" spacing b/n the subfloor panel; problems can occur due to expansion. If a subfloor begins to heave (curl up) at the joints Ditra only has small buffer zone of protection. Pressure points perpendicular to the tile layer can cause tensile stress to appear at the grout joints. This situation is caused by an installer error not product limitation.

If you use Ditra for natural stone, min subfloor thickness before matting is 1-1/8".

01-26-2003, 02:02 PM
I wouldn't consider the bathroom wall load bearing yet. The 3 foot offset matters, as it requires the lower floor joists to carry the upstairs load down to the piers. The lower floor joists are being loaded with the live load from the first floor, and the live and dead loads from the second floor, something that they probably weren't designed to do. I would try to put a new beam below the bathroom wall if possible.

Did your architect design the addition? Was he aware you wanted stone floors?

01-26-2003, 03:40 PM
yes the architect did the addition . he knew we were doing a high end bath with drop in jacuzzi and a separate shower with toilet bidet and double sink.i have a full basement and dont want to put another set of columns in. i will do ceramic if i have to. i have put marble on 2x8 and never had a problem. it was a standard ranch 26 wide with a beam down the center with 2x8 floors.

John Bridge
01-26-2003, 09:29 PM
It's a funny thing. Sometimes installations that aren't supposed to make it do, and installations that should make it fail. No one can predict that sort of thing.

What we try to do is prevent failures. No other way we can do it, sitting this far away from your floor.

I wouldn't chance the stone installation. :)

01-27-2003, 06:49 AM
Knowing what you intend to put in your upstairs bath, I'd have another chat with the architect. If he has structural calculations, ask for a copy. I would be interested in looking at them. If he didn't do any calcs, check back with me anyway.

01-27-2003, 07:31 PM
ok you talked me out of the stone, we are goin with ceramic.i need some sleep. substrate???? i put down 1/1/4 of ply wood ..what should i use for a substrate?. i want to keep the hieght down now that im so high(i wish). ditra or stay with the ply and use the ply with a high strength thinset(oopps did i just curse in tile talk ply as a substrate) well let me have it guys lord knows i need the help thanks by the way my name is chris

01-28-2003, 06:41 AM
Do the Ditra thing.

Chill out, Chris! :D

John Bridge
01-28-2003, 06:25 PM
Hi Chris,

Chill out, dude. :D

Ditra rocks.