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I'm remodeling my mom's bathroom and I'm putting 1/4 inch plywood down on top of the floor to get a smooth surface. The existing floor is strong but there was some deflection in it and it's not as smooth as I would like for stick-down tile.

My question is when screwing the quarter-inch plywood down, I can't get the screws to the bite down to go all the way in. Any answers to what kind of screws I could use to screw it down? I do not have a compressor for a nail gun or staple gun to do it that way and I don't think quarter-inch plywood would be okay with staples.

I just really need to know what screws will bite down and countersink.

When you say "bite down" do you mean:

1. It actually goes through the layer beneath the newly laid 1/4" plywood and simply spins as though it's stripped and will not counter sink, or


2. It will not even sink far enough for the head of the screw to even touch the new layer of plywood?

If it's option 1, are you using a wood screw or machine screw? A machine screw (self tapping or otherwise) would not be a good option for use in this scenario, or most scenarios when the underlying material you're fastening to is wood. The threads are too fine and tend to strip the holes easily. You should be using a wood screw, which has fewer threads per inch (TPI).

If it's option 2, I would agree with @JPhi1618. Consider using a shorter screw so you are not piercing the underside of the floor. This could potentially allow moister to wick in from the underside and rot out the exposed ends of the screws and eventually the subflooring. At minimum, the driving depth of a fastener should be no less than double the material you are fastening. In this case, you are fastening 1/4" plywood, and the math says 1/4" x 2 = 1/2". Therefore, your screw should be at least 1/2" long.

I am guessing that what you mean by a "stick down tile", you are referring to a peel and stick flooring? Similar to found here Home Depot link to the example picture

Personally, I would be hesitant to use a concrete backer, simply because of the amount of dust that sits on top of the backer regardless of how many times you sweep or vacuum, but that's just personal choice. Regardless, I would definitely suggest priming the surface to help ensure a dust-free, clean surface so the tiles will have a better stick-to-it-ness (I just made that word up) and is less likely to have corners curl up prematurely or bubbles appear from what might seem "out of the blue". Best practice, for sure, is to follow the manufacturer's suggestions on underlayment and surface prep.

Hope this helps!

Spax Multi Material Construction Screws are what I use the most. They come in different types but the first two in the photo below will countersink 1/4" plywood easily.

The 1/4" plywood is not the problem if the screws won't "bite". The problem is the material under the plywood which is probably very thin and could be deteriorated especially in a trailer or mobile home.

Screws are the right thing to use. Stapes or nails would pull out. There are special screws made to put down cement board under tiles that have flat heads and wide teeth that will grab the subfloor. They are made for cement board, but should give similar results with plywood. The key is still getting enough bite to countersink the heads.

Example of backer board screws

If the floor doesn't want to handle better screws (and putting holes in the floor of a trailer might not be a great thing), I think that using adhesive would be the next best option. Also, if you can afford a little more weight, using 1/4" cement board might give you a flatter surface.

It seems to me that the reason the screws aren't pulling in is because of the shank of the screw being as thick as the combined material. The OP states that the original floor is solid. Maybe it's a case of 1/2" ply flooring with 1/4" ply going down, using 2" screws with a 3/4" shank. If that's the case a wide shankless screw would be great. Something like a 1" bugle or flat head #8 would work well. Make sure it's finish ply and painting it is a good idea. I put peel and sticks down once and wasn't happy with the process. I used 3m spray adhesive and then layed the tile.

Anatomy of a screw
https://www.google.com/url?sa=i&source=web&cd=&ved=2ahUKEwjC5oz5wIDhAhWE0YMKHQokDY0QjB16BAgBEAM&url=https%3A%2F%2Fwww.kregtool.com%2Fabout-us%2Fnews%2Fkreg-tool-tips-joining%2Fanatomy-of-a-pocket-hole-screw.aspx&psig=AOvVaw1t8n608H3d1xvpxQCXfTCL&ust=1552614224018095