3/4 ply- fine thread screws for subfloor

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  #1  
Old 12-26-12, 10:29 AM
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3/4 ply- fine thread screws for subfloor

i am laying 3/4 ply on top of the original wood plank subfloor (also 3/4) to add support. I had a 25lb box of fine tread drywall screws that i used to screw each board in every 10 inches. Most people are saying to use coarse thread. will me using the fine tread cause issues in the future?
 
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Old 12-26-12, 10:44 AM
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Welcome to the forums.

The big problem, IMO, is you used drywall screws - they are too brittle. Deck screws are the proper choice.
 
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Old 12-26-12, 11:20 AM
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I would use 8d ring shank nails. Deck screws are too expensive and screws in general are too slow.

I do think that drywall screws are not the best choice for this use. While they will most likely never see shear loads large enough to snap them, why take the chance? If you get any movement and a few of the screws snap you'll end up with some serious floor squeaks.

It might be a good idea to look up the fastener schedule for a plywood subfloor/underlayment. I know your 10" spacing does not meet nailing schedule requirements but I'm in the dark about screw fastening patterns. If your project is permitted you might have a problem with the inspector.
 
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Old 12-26-12, 11:50 AM
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the problem is i have already screwed them in. 25lbs of them. Do you think they are going to pop out in the future. i also used liquid nails just as a secondary. there should be no reason to have to take the screws out???? I am thinking now maybe i should just buy a large box deck screws and put 5-6 in each board just as a precaution.
 
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Old 12-26-12, 12:28 PM
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I agree with Wayne. Laying sub-floors was the primary reason why I bought a pneumatic nailer capable of shooting 2-inch ringshank nails. In your case I would recommend either shooting ringshank nails between the existing screws (you can rent the nailer and compressor if necessary) else use the deck screws.

Drywall screws are really ONLY for drywall. Fine thread screws are primarily for steel studs although they can be used for hardwoods if a pilot hole is first used. Coarse thread screws are used with most wood projects.
 
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Old 12-26-12, 04:03 PM
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Hopefully you used Liquid Nails - Subfloor. Unless indicated on the tube for subfloor all other liquid nails are not rated for flooring use.

Just ask yourself, how many drywall screw heads snapped while you were installing the subfloor. My guess is more than a few if you were sinking them tight enough to hold the subfloor steady. The fine threads also do not leave enough wood between the threads to really give them a long term prospect of holding tight. You may have even stripped a few screw holes during the process.

Forget that you have already spent hours sinking 25 lbs of screws into the floor. Bite the bullet and follow any of the suggestions above. In the long run, you will be glad you did. Remember, only takes one squeak in a floor to drive you crazy.
 
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Old 12-26-12, 05:22 PM
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You don't need another opinion, but I can't help it. What czizzi said. Bite the bullet and do it right. You will have problems down the road if you don't. Ring shanked nails or screws (decking) makes little difference, but fine thread sheetrock screws won't hold.
 
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Old 12-27-12, 10:26 AM
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since i already have about 30-40 screws in each board and also used a (subfloor) liquid nails for underneath. i think i am going to just add 10-15 decking nails to each board to make sure we have no movement. do you think natural expansion of the wood would be enough to sheer the screws? I also have screwed these down in the home were the temp was approx 50 deg weather.
 
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Old 12-27-12, 11:39 AM
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Your question was already answered. Either take their advise, or take your chances. It's up to you now. Only one person will be responsible for the outcome.
 
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Old 12-27-12, 11:50 AM
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Personally, I can not give you a guarantee. Whenever I come across these types of screws (course or fine thread) during a remodel, I back everyone out and replace with exterior decking screws. They are a PITA as most of them are stripped out in the hole. In order to back them out I have to get a putty knife under the head of the screw and pry up until the threads catch on something and they back out. The only ones that stay are the ones with the snapped heads.

It is not just lateral movement that can cause these screws to fail, but also bounce in the whole floor system can stress the heads. You came here seeking advise, which has been provided. It is up to you to decide on how you will proceed. Sorry you were not thrilled with the direction we recommended. You seem to want to hang on to the notion that what you have already done will suffice. I would feel comfortable about leaving them if you drove a deck screw adjacent to each and every drywall screw.
 
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Old 12-28-12, 05:47 AM
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just to update you.. i went out and purchased 4 5lbs boxes of deck screws. i started putting screws approx every 12 inches which equates to around 35-40 screws per board. i feel way more comfortable laying oak flooring over the subfloor now. the screws are so much stronger and i can feel the difference.... now taking the old 1 5/8 dry wall screws out..... Started one board but its almost impossible. Having 40 decking screws and 50 drywall screws in each board i think should protect against any squeaking in the future.

Thanks for the quick advise BTW.
 
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Old 12-28-12, 07:13 AM
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Your original drywall screws were not long enough anyway. 2 layers of 3/4" subfloor is 1 1/2" thick, 1 5/8" screws did nothing. But it begs the following question. How long were the deck screw? and Did you screw the 3/4" down to the floor joists?
 
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Old 12-31-12, 10:42 AM
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i have 3/4 in planks that were screwed to the beams. the 3/4 ply was screwed to that in the opposite direction. i used 2 by 8 deck screws. two inches should do the trick.
 
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Old 12-31-12, 01:32 PM
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To clarify for those who will read this thread in the future, I see what you have done is this: Screwed your 1"x subfloor planks to the floor joists with 1 5/8" fine thread drywall screws. Then randomly layed 3/4" x 4' x 8' OSB subflooring to the 1'X subfloor planks. Then based on our recommendations you added a number of deck screws. I'm hoping I have followed this thread incorrectly.

For all the previous stated reasons, this was the completely wrong approach.

The correct procedures should have been:

-Screw or Ring Shank Nail off 1"x plank subflooring, remove any loose nails or nails that did not hit a floor joists during the initial lay down when the house was built.
-Lay 15# felt or rosen paper down as a sound deadening barrier.
-Overlay with 3/4"x4'x8' Advantech or Home Advantage T&G OSB subfloor perpendicular to the floor joist and screwed to the floor joists with 2" to 2 1/2" deck screws. Seams in the OSB should split and share a floor joist with both sides of the seam screwed to the joists. Screwed every 6" the seams and 10" to 12" in the field.
-3/4" 4' x 8' Advantech or Home Advantage sheets should be staggered by 1/2 sheet on each successive row.
-Lay 15# felt or rosen paper down as a sound deadening barrier
-Install 3/4" hardwood naildown planks set perpendicular to the floor joists.
 
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Old 01-01-13, 04:59 AM
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I'll have to disagree slightly on the attachment of the advantech. Normal installation over an existing subflooring will not call for tar paper between the layers (although since you have planks it won't matter since it can breathe) and you don't screw the second layer into the joisting. It must be a "slip" installation and the screws should intentionally miss the joists.
 
  #16  
Old 01-01-13, 09:31 AM
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Larry - you've caused me a morning of reading tech bulletins on subfloors on hardwood installations. No where did I find a definitive "miss the studs" on the 2nd layer of subfloor. Yes, I agree in tile applications you need to miss the studs on your underlayment to provide for a slip sheet and/or uncoupler. What it doesn't explain is a traditional nail down hardwood floor over a single layer subfloor install that is glued and screwed. There is no "slip" in a single layer system. The best tech manuals I found are here, one for plywood and one for OSB.

Plywood
http://www.tecotested.com/techtips/p...plicationguide

OSB
http://www.tecotested.com/techtips/p...plicationguide
 
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