plywoodscrewssubfloor
I was using all-purpose screws (1 1/4") to attach my second layer of plywood to the under layer. The top layer does not get screwed into the floor joists. A lot of the screws just spin and don't sink into the floor like I want them to.
Am I using the wrong screws?
Would like to put in a suggestion for either Schluter Ditra or Laticrete Strata-mat.
As uncoupling membranes, they effectively stiffen floors by unitizing the tile layer. For stone installation, Schluter recommends double layer of underlayment. The second layer should be offset from the first layer, not following seams. The second layer should only be attached to the first, not through to the framing. The total thickness only has to be 3/4, but can be thicker as necessary for level matching. The first layer should be at right angle to the joists, along the the long direction of the ply.
Ditra stone tile install
Ditra plywood install
excerpted from Ditra installation handbook
I would reset all the nails that are holding the 1X6s,making sure the nail point has found new wood by setting the nail head below the surface by making the last few strikes with the hammer at an angle to dimple the wood with the nail head. With the nails drawn tight, that should eliminate any potential floor squeaks, but for redundancy add a screw between all the nails. Do not add no more than that, the potential of splitting the joist tops. So if you can, run the screws in at an angle to get the screw to not go the same direction as the other nails. It is a minor detail, but that is what I would do.
After your existing subfloor is secured do what you can to get your T&G joints to break near the center of the 1X6, running you plywood the same direction as the 1X6, perpendicular to the joists.
In my opinion, 3/4" along with the existing 1X6, is overkill on the subfloor/underlayment combination, unless you are setting tile. 5/8" T&G will be a lot easier to carry upstairs and still give a T&G feature which is good. In a minimalistic approach 1/2" underlayment grade plywood will work very well too with the re-secured 1X6. DO make sure it breaks on the center of the 1X6s, cut it if it is not, I refer to NON T&G plywood here so ripping an inch or two off the occasional piece does not matter. What matters is it breaks on the 1X6 everywhere. After that 1 1/4' OR 1 5/8" screws on a 8" grid pattern and construction adhesive will tie it all together. There is no need for 3 1/2" screws for any reason. Maybe 2 1/2" in the joists here and there if you choose, but remember the thing mentioned about too many fasteners in the tops of the joists.
Best Answer
You'll need to pilot and counter-sink screws like that, or try switching to a self piloting, self counter-sinking screw like Gold Star or similar. The problem with all purpose screws is that the blunt tip just flexes the fibers out of the way, reducing the amount of material the threads can get a hold of. With a screw that short it doesn't get enough bite to pull the head flush so it strips out. With a Gold Star, the burr on the tip severs the fibers, allowing the threads to bite in all the way around, then the nibs on the bugle help the head burrow in so you don't have to counter-sink.