Correct Subfloor? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-24-2017, 10:38 AM
New to this site but I've been reading a lot on here. I keep stressing about my subfloor. Is this enough or do I need more? Looks like 1/2 inch with 5/8 on top. I'm installing 12x24 porcelain tiles with 1/4 inch hardibacker. Deflection calculator says I'm good for tile.

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01-24-2017, 02:09 PM
Maybe, maybe not. FWIW, there is no 1/2" panel that comes with T&G, and the first layer must have the long edges supported either with T&G, or by blocking. If they chose to use 1/2" to save money, it is unlikely that they installed blocking to support those edges. Also, no current building code allows 1/2" as the bottom layer of a subfloor, and all of the tiling specs assume that layer is correct and to code. Yes, I know builders did it (mine was built that way!), doesn't make it right, though. THen, the second layer MUST be installed properly to provide the needed strength. There's an article in the 'liberry' that describes how to do that.

01-24-2017, 02:41 PM
I guess I'm confused. So these 2 layers will not be enough? You're saying that I need to add another 3/8 to the floor before installing tiles?

01-24-2017, 05:32 PM
A first 1/2" layer, without the long edges supported, is essentially not worth much of anything. It is really hard to anchor anything to it because there's so little for a screw (or, maybe a ring-shank nail) to hold. Then, the second layer must be installed properly which means no joints line up, the ends offset, the second sheet not anchored to the joists, proper anchors at the required spacing.

One of the moderators will throw their thoughts in here eventually, but from previous discussions, I think I've got it along their general recommendations.