Luan as an underlayment for tile

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Old 03-10-07, 09:25 PM
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Luan as an underlayment for tile

Why can't cermaic tile be laid over luan plywood?

Is it just a question of 1/4" luan over a normal 3/4" thick T&G floor deflects foot traffic poorly and causes too much bounce in the floor to support the tile? Or is it something in the luan that thinset will not bond to correctly?

The store rep, wihtout even seeing my floor is telling me I need to rip up the 1/4" thick luan and put in 3/8" plywood to install ceramic tile. How much more deflection can an extra 1/8" of floor width provide?
 
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Old 03-11-07, 06:06 AM
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You need a minimum of 3/8" in a wood product to achieve some structural strength. Luan being from mahogany presents two other problems, regardless of the thickness, it is a very soft wood to begin with. Try rolling a heavy refrig over it and watch the wheels dig a gouge into the luan. Second, it has certain oils inherent in it that react against the latex in modified thinsets and wont allow a complete bond of the thinset. If you look at any bag of modified thinset you will see it says to NOT use it over luan, it will void any and all warranties and you will be left to scrape up loose and broken tile within the year.
 
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Old 03-11-07, 09:46 AM
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Okay, great info.

As a second opinion, what would you suggest to put over this floor to lay ceramic tile. I really don't want to pull up the luan and then pay to have the tile guy put another layer put down

I have 3/4 T&G plywood as the bottom layer, on top of that I have 1/2 OSB and as a top layer I have the luan which I pulled off the vynyl. The 3/4 and 1/2 are on all the floors so adding another 3/8 ply and 3/8 tile would add 7/8 lip from the carperted area. Is this too much?

Can cork be glued down over the laun?
 
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Old 03-14-07, 03:17 PM
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As Bob said the luan has to go. Remove the luan and either put down 1/4" cement board or an isolation membrane like ditra. Luan over time will compress and cause the tile installation to fail. It should not be used in any layer underneath tile.
 

Last edited by HeresJohnny; 03-14-07 at 03:50 PM.
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