# subtrate for bathroom tile install



## AustinDB (Sep 11, 2006)

getting ready for a 13" stone tile install over 3/4" plywood covered w/ vinyl. I'm guessing the vinyl is installed over a layer of luaan or equivalent. Should the vinyl/luaan be pulled up before putting down a layer of 1/2" plywood, thinset and CMU? Is there any additional need for a moisture barrier on a bathroom floor install? 

next question-the 6x9 foot bath has a 2x5 sink-common sense says best job is to pull the cabinet, is it also accepatable to leave in place and install new flooring layers? I'm thinking about the extra work that may be necessary in prepping/painting the wall from removal of the cabinet as well as extending fittings.


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## firemike (Dec 11, 2005)

> Should the vinyl/luaan be pulled up before putting down a layer of 1/2" plywood, thinset and CMU?


 Most definetly!



> Is there any additional need for a moisture barrier on a bathroom floor install?


 Not usually.



> common sense says best job is to pull the cabinet, is it also accepatable to leave in place and install new flooring layers?


 How did you bid it? Many people tile around them, I prefer to pull them if at all possible, but sometimes circumstances dictate that they be left in palce. 

If the floor meets the installation requirements for Schluter Ditra, you might consider it instead of durock or other cement board, makes the installation thinner, less work, and a little more forgiving. http://www.schluter.com/media/brochures/schlueter_hb_ditra_us_2007.pdf


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## ChrWright (Jul 17, 2007)

For natural stone, Ditra requires double layered subfloor regardless of joist spacing.

I would take everything out down to the 3/4" subfloor and then install 1/2" Deshied or cementious backer (Durock/Permabase) over thinset. You might get away with 1/4" backer for a better door transition--but I'd be sure the floor was extremely solid & wasn't at all compromised by water damage.

If you don't remove the vanity, you may have a nasty looking gap at the floor to deal with when you're done--new toekick, shoemold, etc.


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## JazMan (Feb 16, 2007)

Chris,

Maybe you weren't aware of it, but he needs a double layer plywood subfloor for a CBU installation too. Installing natural stone over a single subfloor is risky. If his joists meet L720 deflection he'll then be fine. 

Chevy, did you check those joists for a rating? Do you have a span chart?

Jaz


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## AustinDB (Sep 11, 2006)

I have span charts galore...figuring out how to measure deflection, I don't know how to do. Before removing the vinyl and underlayment, how would you determine the joist spacing? How would you measure to see if you're within the limits?


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## JazMan (Feb 16, 2007)

You don't actually have to measure the amount of deflection, the joists span charts will tell you what you need to know. As for the deflection between the joists, it has been determined that a double-layered subfloor will handle natural stone. Most recommend 3/4" + 3/8" min. Your plan to add 1/2" should be fine as long as the joists meet L720. Then adding either a tile backer or Ditra of course.

There are instruments that will measure deflection if you're really interested in that. You can also make a jig that will also do it. However it is not the job of a tile setter to go thru all that.

You asked; *Before removing the vinyl and underlayment, how would you determine the joist spacing? *I'm not sure I understand the question. You determine the spacing of the joists by measuring it. 

What deflection rating do your charts give you for those joists?

Jaz


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## AustinDB (Sep 11, 2006)

the charts are in a book I have, which I have not cracked open. 

The question was, as you go in to view a job for the first time to put together a bid, how would you determine what type of joist or spacing you're dealing with? How can you tell if they're 16"OC or 24"OC as the floor is intact. It could be possible to walk down to the first floor (assuming this is a 2nd story bathroom) and look for nail pops in the ceiling. Beyond that, are the joists souther pine, spf#2, fir #2 or other type of species, which are used to determine the load level. 

Is there a product which can be laid on top of the typcial 3/4" subfloor which acts as a stiffening layer AND bonding surface for tile or stone, providing the minimum 9/8" subfloor?


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## JazMan (Feb 16, 2007)

If you can't get access to the crawl space, basement or the job is on the second floor and the ceilings are all finished, all you can do is guess. From experience you might be able to tell simply by walking and jumping of the floor. You should do that even with known subfloor members. 

All modern homes should meet minimum L360 deflection, some are built to L480. I'm sure you know that, and so that is good enough when installing ceramic or porcelain tiles. All you need to do is install a proper CBU or membrane. The only way to stiffen the subfloor between the joists is to add more plywood. 

I don't know what you mean by this: ...*"providing the minimum 9/8" subfloor"?

Jaz
*


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## Forry (Feb 12, 2007)

9/8"=1 1/8"


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## Mike Finley (Apr 28, 2004)

JazMan said:


> If you can't get access to the crawl space, basement or the job is on the second floor and the ceilings are all finished, all you can do is guess.


In regard to determining joist spacing, you can use a stud finder on the ceiling below and determine your joist spacing pretty quickly.


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## JazMan (Feb 16, 2007)

Yes of course, a stud finder from below or nail pops as mentioned.

OK 9/8, I was thinking in quarters like 5/4 not eights.arty:

You need at least 1 1/8" of plywood plus the proper CBU or membrane when installing natural stone, more would be advised if you can stand the height. 

Jaz


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