To glue or not to glue

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Old 11-07-14, 10:12 AM
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To glue or not to glue

Installing 5/8" ply atop existing subfloor for 9sqft +/- entry way for 1/4" hardi and tile.

Glue and screw 5/8" ply with liquid nail subflooring to existing subfloor or just screw only? 6-8" oc of course.

Thanks in advance
 
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Old 11-07-14, 10:15 AM
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Screw only and intentionally miss the floor joists.
 
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Old 11-07-14, 11:44 AM
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Just curious, why intentionally miss the joists?

- Peter
 
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Old 11-07-14, 12:12 PM
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Chandler's advice - you want a slip between the layers.
 
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Old 11-07-14, 12:25 PM
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Only fasten the underlayment to the subfloor. It may have to be removed some day. Using construction adhesive will create voids where there is no glue. Use 1" screws and you won't have to worry about hitting the joists.

Don't forget the thinset under the concrete backer & tape the seams.

Jaz
 
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Old 11-07-14, 03:42 PM
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Where does the slip occur if you are screwed to the subfloor anyway, and the subfloor is attached to the joists?
 
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Old 11-07-14, 04:08 PM
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Not really slip Droo...just expansion and contraction. Since the top layer is layed differently, it will move differently. Just screws gives it that extra "edge" thats needed. I've always heard the same thing...glue and screw the first layer, let the top layer "float"...not like a floor of course.

I wish they had done the glue and screw at my last house in VA...second floor squeaked like a pig til I used the "Squeak-no-more" (or whatever it was called) system on the worst areas.
 
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Old 11-08-14, 04:40 AM
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I see how that happens without using glue, but how would avoiding the joists change anything? And why is the expansion and contraction different if you have two layers of plywood? I don't see the thickness affecting that very much.
 
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Old 11-08-14, 05:53 AM
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Droo, the way it is explained is if you tie both layers to the joists, you lose the ability of the top layer to move, even if it is just a slight amount. By placing your screws sans the glue in the field away from the joists, it gives both layers the expansion and contraction needed to keep the floor flat. Yeah, I know it doesn't make physics sense, but neither does floating basement walls in Denver, to me. How does a slab lift and drop without lifting and dropping the entire house???
 
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Old 11-09-14, 06:54 PM
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Because the slab isn't connected to the foundation and weighs less than an 80 ton house.

I understand not using the glue. I see no difference in attaching to the joists or not.
 
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