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DENNIS R 06-17-2011 12:35 PM

Travertine floor- correct info new thread
Hello everyone,
Based on the feedback I started a new thread with all the details on the construction for my new addition on second floor master bath Travertine tiles. Can someone confirm the structure and floor strength, deflection ratio, etc.

Here it is

18 by 18 honed and filled Travertine
Joist 2 x 10, doubled every other.
Span is 15 ft
Joist 16 inches on center
Spruce Pine , #2

osb 3/4 boards, screwed.
additional 1/2 boards
1/4 inch dur-rock
1/8 thinset plus 1/8 thinset for the heated floor system.

The shower did NOT get the extra 1/2 underneath as that was built already. The joist under the knee wall in the shower has a double joist. The shower is on the back of the wall and is approx 5 ft by 7 ft.
Is the shower part ok ? It is porcelain and some stone.

1. How is the structure ?
2. Deflection ratio ok ?
3. Should this be sufficient ?

The cracked tiles I have are in the old part of the addition.

Thanks for the help.

JazMan 06-17-2011 11:18 PM


Your floor is not stiff enough for natural stone tiles. It may not be stiff enough for ceramic either.

Many building departments allow a lower standard for 2nd floor "sleeping rooms". I think they allow L240 where the basic standard is no more than L360 deflection. Natural stone should start with framing that meets L720. You're not even close.


DENNIS R 06-18-2011 06:50 AM


Thanks for the reply and right to the point. I had flat out asked the engineer if for this floor it needs to start with a stronger structure and he said no. Matter of fact he said he never heard anyone use the standard of an L720..only L600. He claims the every other double joist started the floor at L420 and with the subfloors brings it to L600.

The floor below this second floor addition was to support stone and ceramic tile, I have questioned this as well and believe this to be substandard. The room has a stone fireplace, hearth floor stone tile and the rest is hardwood.

Here is the info for this floor:

2 x 8, joist 16 on center.
span 10 ft 5 in
osb 3/4 boards
#2 , SPF

Jaz, do you or would anyone on this site be certified as an engineer or what level of authority can state this firmly.


DENNIS R 06-18-2011 11:36 AM


My next question to you is what is the fix ?

Can it be supported properly at this point ?

What needs to be done ?


Bud Cline 06-18-2011 12:15 PM

This so-called "engineer" must have been living in a tree house somewhere.

The Tile Council of North America (TCNA) is the governing authority (if there is one) for ceramic tile installations. The Marble Institute of America (MIA) sets the standards for natural stone installations. Then there is the American National Standards Institute (ANSI) that also prescribes suitable methods.

Do you mean to tell us THIS engineer has never heard of those forty and fifty year old entities? Which railroad does he work for?:)


My next question to you is what is the fix ?

The first thing you need is a different and more qualified engineer.:yes: One that graduated from an engineering school and is not at this time serving his internship.


Can it be supported properly at this point ?
Ask your new engineer.:yes:


What needs to be done ?

Ask your new engineer.:yes:

If you were to go to their respective websites, you could purchase their recommendations for a reasonable fee. THEN you would have the information in your hands and wouldn't have to depend on the information you are getting from these forums and some un-informed so-called engineer. In fact the TCNA offering can include the related information from ANSI all in one purchase.:)

JazMan 06-18-2011 10:05 PM

I agree with Bud, this engineer is not calculating deflection correctly. For ceramic and stone you also need to consider "point load" deflection, not just what the entire floor can hold. It's not good the have tiles crack above every other joist, and the subfloor adds little or no stiffness the the joists, it just adds stiffness between the joists.

If your framing joists were not doubled at every other joist, you could safely have a span of about 11' for natural stone to meet L720. There is no grade of spruce that will span 15' for natural stone. Matter of fact you can not span 15' and even meet L360 with single joists. Granted, doubling every other joist helps to get you over the basic minimum, (L360), but that does not help you with natural stone. There's the answer, ditch the stone and get ceramic/porcelain instead.

We could continue this thread with other deficiencies, but unless you're ready to rip out the ceiling below and add framing, you need to reconsider your tile choice, or do it wrong anyway.


DENNIS R 06-19-2011 07:58 AM


Thanks again for your insight. We in fact plan on having ceiling cut open and finishing it as planned. With that in mind what are the correct steps to fix.

Also, I would like to fix the other deficiencies also. Please feel free to elaborate so I can get everything corrected.

Please comment on the section of the shower 5ft by 7 ft that has only a 3/4 osb underneath before they started with mortar.

what is the calculation for point load deflection ? What do I have and what should it be ?

The goal is a fix and the correct fix and steps I need to do this correctly. Please don't hold back..


Bud Cline 06-19-2011 01:05 PM

Please don't hold back...:no:

JazMan 06-19-2011 09:02 PM

Some of your question require an engineering degree and of course being there.

The easiest fix I can recommend from here is to shorten the span by installing a supporting beam at or near midspan. This will fix the framing.

You will also need a double layer subfloor/underlayment for natural stone. You mentioned 3/4" OSB, then you said

osb 3/4 boards, screwed.
additional 1/2 boards
I guess sheets of OSB & plywood are "boards" to you. The underlayment is fastened to the subfloor only and no glue.

Follow with the 1/4" CBU set into fresh thin set mortar and fastened with the special screws or roofing nails. Tape the seams and smooth with thin set, preferably as you're setting the tiles.

Before all this, be sure that the joists are in plane with each other. The finished-ready for tile floor must be very flat.

OH.... why thin set for the warming mat?


DENNIS R 06-20-2011 08:19 PM


Had a meeting with a Stone Tile company and they confirmed the following;

The mortar used for the large stone tile was incorrect ( Mapei Tile Mortar )
The cracking in the old area could be from the lack of coverage under the tiles.
The contractor was there and agreed to replace and redo the tile.

They also confirmed my kids bathroom floor was installed with insufficient coverage and will be replaced. This one had the sanded cracking sound underneath.

I still need to correct the the sub standard L420 total load L600 that his engineer has stated as the numbers.

I am not sure of the quality of the osb boards but it was two layers of the same boards, 3/4 to the joist and 1/2 on top. Is this ok or does this need to be replaced as well ?

The original part of the remodel has a plywood from 1986 nailed in and 1/2 osb nailed over that..what should take place here if we are ripping up the floor anyway ? I wonder if the old joist need some help ?

FYI, this site has been amazing and extremely helpful. What a great group of people here..


JazMan 06-20-2011 10:49 PM

The is nothing wrong with Mapei mortars. I believe you were told that in the other thread. He just used the wrong one. Maybe he has little experience or maybe he didn't or couldn't read the instructions on the bag.


I still need to correct the the sub standard L420 total load L600 that his engineer has stated as the numbers.
Since the Stone Tile company is paying for the engineer, (actually you are indirectly), and you are leaning towards his advise, what does he suggest? I would like to see where the TCNA, MIA or any reputable organization says L600 is the number for stone tile floors. He won't be able to show you those reports, cuz the recommended number is L720.


I am not sure of the quality of the osb boards but it was two layers of the same boards, 3/4 to the joist and 1/2 on top. Is this ok or does this need to be replaced as well ?
I have no idea what you've got there. What does the engineer say?


DENNIS R 06-21-2011 05:57 AM

Thanks Jaz.
Correct regarding the mortar, I believe the Tile sub chose the $10 bag instead of the $20 to save money is my thoughts.

I did not have the engineer out yet, spoke with one. He will be charging $250 to come out and evaluate and $250 for a written proposal of the fix, does this sound correct ?

Also, please share your thoughts on the joist numbers.
In my flooring what are the answers for these three questions,

1. Doubling every joist with 2 x 10..what is the L number ?
2. If I double each joist and add the beam at the center which you suggested , what is the L number ?
3. if I leave it doubled every other and add center beam , what is the L number ?

Bud Cline 06-21-2011 05:00 PM

Jaz your PM Box has exceeded its limits. Time to clean house.:yes:

JazMan 06-21-2011 09:01 PM

Yea yea I know. I'm a sucker! :whistling2:


JazMan 06-21-2011 09:15 PM


If he's willing to do it for $500, and you're willing to pay him $500, perfect.

I charge $250 and up for up to one hour of verbal advice at the local job site. A simple letter of my conclusions is $250. I limit my opinions as it relates to tilework, not general structure.

I've recently set up a PayPal account for telephone & email consultations. Those rates are a little lower. I am sometimes asked to look at a few problems away from the home base. Why? I'm not sure since that costs much more.


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