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the carpenter 05-01-2010 10:48 PM

1/4" subfloor for tile?
I'm installing slate tile in my kitchen and was under the assumtion that 3/8" plywood was a MINIMUM standard for tile.
A tile installer recommended using a 1/4" underlay so it would line up better with my 3/4" hardwood and avoid the toe stubbing.
The house is new construction, 19.2" floor trusses, 3/4" OSB subfloor.

Has anyone ever used 1/4" plywood or is there another 1/4" product out there that would work?
Maybe the tile guy wanted me to put the 1/4" under my hardwood.

racebum 05-01-2010 11:25 PM

i'm lost somewhere. your subfloor should be at least 3/4" fir plywood, on top of that you can use 1/4 or 1/2 cement board to get the desired height.

where i'm lost is with the 3/8 plywood. i can't imagine any house having a subfloor that thin sooo..what were you referring to? are you talking about installing plywood over the osb?

Bud Cline 05-01-2010 11:45 PM

Not sure where you guys are getting your information and if you continue down this path it's going to be very costly for someone.

Stone floor tile installations REQUIRE TWO LAYERS of plywood with a minimum combined thickness of 1-1/4".

Plywood 1/4" thick is NEVER used in a tile installation, the absolute minimum is 3/8". By the way just for the sake of conversation...luaun plywood is FORBIDDEN, period. Has nothing to do with the above proposal just trying to set the record straight.

Minimum subfloor thickness is generally a minimum of 5/8" [by code] with some areas of the country requiring a 3/4" minimum. Has nothing to do with tile installations tho. Stretch the joists out to 19.2" or 24" on center and someone better be following some industry recommendations if they only want to do the job once and do it right the first time.:)

JazMan 05-01-2010 11:51 PM

There's a bit of confusion in your plans. If you continue you'll end up with cracked grout and broken slate tiles. BTW, I wouldn't let that tile installer near my floors.:no:

You can not successfully install natural stone tiles the way you're planning. It'll be a mess within a few years.:yes:


the carpenter 05-02-2010 09:42 PM

so yes, sorry about the confusion. Perhaps my lingo is incorrect.
from the bottom up here goes.
-floor trusses at 19.2" o/c
- 3/4" tongue and groove OSB subfloor
- now I need some underlay for the tile which I thought had to be a minimum of 3/8 plywood. My question is ,"Has anyone heard of a 1/4 inch product that will provide the support necessary for tile installation?"

Once again, sorry for the confusion...

the carpenter 05-02-2010 10:33 PM

Racebum said something about 1/4" cement board so I quickly visited the Hardie site......

Is their 1/4" cement board fairly rigid and can it be used instead of 3/8" plywood underlay? I've heard of lots of guys using the 1/2" cement board for underlay but I've never seen the 1/4" around here before.

Russman 05-03-2010 07:04 AM

tile install
I only heard of cement board at 1/4" used on floor. You need to put a 1/4" bed of mortar down prior to install. Then install the cement board down with waterproof screws while the mortar is still wet. Remember, your tile is only as good as the strength of the floor below. How many times have you heard from someone that they have a couple crack tiles etc. It is worth the money to pay for a quality tile installer to do job.

Good luck

Bud Cline 05-03-2010 04:40 PM

Cement board that is 1/4" thick is for floors only. No cement board offers any structural benefit what-so-ever. Half inch is not better than quarter inch.

Cement board is installed in a fresh bed of thinset using a 1/4" notched trowel NOT a 1/4" of thinset. The screws to be used are NOT waterproof screws, they are alkali resistant screws.

The subfloor structure must meet a minimum deflection of 1/360.:wink:

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