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Tile underlayment question


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My son has put 5/8 plywood down on top of solid decking in his kitchen. Finish floor will be wood like tile. We're wondering if he needs to put cement board down or Red Guard, or nothing at all? Would Red Guard just around the plumbing areas be of any benefit? I have an entry way with tile on plywood and an area upstairs in front of our shower the same way that has held up for 20+ years.

What'cha think?

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Red Gard can work fine. Or, stone board over what you've got, bedded in thinset. Depends on the grade of tile.

Personally, I've become a complete Schluter devotee. Ditra....and do it correctly.

It eliminates multiple substrates and all the hassle, cost, and uncertainty they create. Now that he's got a couple layers of subfloor, I don't know if it's necessary, but I'd use it anyway.

And, it's Big Box available.

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I've installed lots of tile floors. More than I care to remember, and I've used 1/4 Hardi on all of them with no failures. Put a screw every 6" in the grid and it works. The last couple I did I was tempted to use the Ditra, but was in a rust and didn't have time to make a mistake and be forced to back up.

Check the floor for any bad dips and humps. Be sure to float those out before installing your backer. Those wood grain tiles are long and skinny, and very unforgiving when a dip shows up. You try to span a low spot and the tiles will break.

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Those wood grain tiles are long and skinny, and very unforgiving when a dip shows up. You try to span a low spot and the tiles will break.

Yep. Float the low spots before you ever get to substrates.

Hardi works fine. It all works fine if one does what they're supposed to. I moved away from Hardi for lots of reasons, but not because it doesn't work. It's all the other stuff....it's heavy, it's dirty, I hate cutting it, I hate disposing of the waste, and it's another additional thickness to integrate into transitions. It's old technology when much better stuff is available.

Folks are scared of Ditra because of all the admonitions to "make absolutely sure you install it correctly or it's horrible". If one goes through the list of requirements, it's really very basic, simple stuff that's easy to accomplish. Folks are also dismissive because it's old guys not wanting to change.

I like Ditra because it's light, easy to transport, easy to cut, and it works incredibly well. Once one uses Ditra, or really, any of the new tech (KERDI!!), it's tough using the old stuff. The new stuff works better. It's a fact.

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Ditra or backer board. Either one. If he's already got plywood over solid decking then he probably doesn't need or want the extra thickness of the backer board. Ditra will be slightly thinner.

The one thing I wouldn't do is put the tile directly over the plywood. If the plywood gets seriously wet (from a leaking dishwasher, for instance), the tiles will pop loose. Red Gard might offer some protection against the plywood getting wet, but it's kind of a bassackwards way of dealing with the issue. You've been lucky with your floors. Whenever I find tile applied directly over plywood, I *always* find a loose tile somewhere.

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