How do you do this ? (please read)

[madmax64]

Highup, I am following your post #5. I just finished sanding plywood seams. I am going to use a cement-based floor patch to fill in "holes" (gaps, etc) and use cement-based self-level underlayment (Henry 555). Then cover the entire subfloor with 1/2" plywood, correct? How do I fasten 1/2" plywood to the subfloor? (how far between two nails or screws)? The existing wooden subfloor is 3/4" thick. Should I use 1 1/4" nails or 1 1/4" screws?

let me know and thanks!

 

[highup]

I believe the half inch is nails or screws every 6 in in the field and probably 4 inches on the seams. I'd have to double check that. There are nailing schedules online that would tell the spacing for different thicknesses of plywood. Screws are usually better but galvanized ring shank nails can be a lot faster. When driving them in you'll know by the seal if they're grabbing and holding well. They're also cheaper than screws.
That said if you buy screws the ones that seem to work best for me are the torx head screws. They don't strip out the heads like Phillips screws and some lumber yards and stores like Ace might have a bin of screws instead of boxes.
I'll check on the nail schedule.

 

[DarisMulkin]

That said if you buy screws the ones that seem to work best for me are the torx head screws. They don't strip out the heads like Phillips screws and some lumber yards and stores like Ace might have a bin of screws instead of boxes.

If using screws do not use drywall screws, they snap off really easy. I'd use deck screws.

 

[highup]

I use my phone for the internet searches and it just doesn't come up with the results like a computer does.
I'm seeing 4 in on the edges and 6 in in the middle and I'm also seeing 8 in on the edges and 10 in the middle.
if you're using a computer for your searches you might be able to find results easier than I can.
Just type in nail schedule for 1/2" underlayment.
Two things to do if possible.
If you have space stack the plywood leaning up against the wall instead of laying flat on the floor so I can acclimate to the house for a day or so.
The other thing is nail from the center of the board outward. I did a house one time and the contractor nailed all the seams in the plywood and then fastened the center. That is terribly wrong. You want a nail from the center outward. I usually run a row of nails down the center of the board lengthwise then through the center of the board crosswise. Then nail from the center outward in each of those four quadrants. This forces any unevenness in the plywood to the outside edges instead of forcing it towards the center of the panel.

 

[highup]

If using screws do not use drywall screws, they snap off really easy. I'd use deck screws.

Thanks I forgot to mention that. A lot of people use drywall screws because they're cheap. So are ring shank nails and as long as they drive in nice and solid into the subfloor those work also.

 

[highup]

Also never install panels of plywood so all of the corners line up. Stagger each row of plywood 16 inches or even 4 feet. Like I said there are diagrams on how to do this and you'll find those when you're looking for nailing schedules.
Also be sure to offset your new plywood so that it doesn't line up exactly on the seams of the existing plywood.

 

[madmax64]

Can you get me some links on nailing schedule, how to place the plywood over the existing subfloor the right way, etc? that would be very helpful.

I'll go with ring shank nails (more faster than screws). I did some search on nailing schedule and it is very confusing. Some say to use 6d nails which is 2 inches long. My existing subfloor is 3/4" thick (plywood) and the new plywood will be 1/2" thick. Total thickness will be 1 1/4". I should get ring nail shank, 1 1/4" long???

I just looked up in Home Depot website on plywood, they have 15/32" (0.438) and 19/32" (0.563) sheathing plywood. Do you think I should go with 19/32" which is a bit thicker than 1/2"?

Existing plywood subfloor have some "dips" (low point of the subfloor), maybe 4 or 5 different places. They are about 1/8" deep, maybe a bit more than 1/8". I will fill them with self-leveling cement. Is it OK for new plywood to cover them? and is it ok to put nails over them (that will go through the self-leveling cement)?

Let me know and thanks so much for your help. I just want to get my project done soon. Tired of looking at wooden subfloor in the living room, dining room, hallways and kitchen for the past several days.

 

[highup]

I use my phone for internet searches and the results I get compared to a computer are not so good. If you have a computer you can find better information than I can.
Basically you don't want the seams in the new plywood to line up exactly on top of the seams in the existing plywood floor, so you need to snap a chalk line at least 2 in and 6 or 12 in is better, the length of the room. Outside walls in a house are usually the straightest so measure out from the exterior walls at one end of the room and do the same at the other end of the room then snap the chalk line.
Start installing your plywood at one end of the room and once fastened place the next sheet along that same chalk line and install that sheet. you don't need to do all of the plywood seams at this point if you don't want to but nail the field on each panel.
When you install the next row of plywood, cut off two feet or so from the starting sheet so that you don't end up with four corners of plywood all meeting at the same point. You want the sheets staggered a little bit. One foot, two feet, four feet, whatever just don't let all four corners line up, and don't let the seams line up with the original plywood that's on the floor now.
Inch and a quarter or inch and a half coated ring shank nails should be fine. Use the galvanized or coated ones.
Again on the nailing schedule I see different things mentioned from different manufacturers. I'm guessing 8 in on center would work, but you could always make it less than that to be safe. On the seams you want to do it closer.
The nails will not have any trouble at all going through the filler.
So it sounds like you're going to be nailing. Here's one trick that will help out a lot. Lay a piece of 50 or 100 grit sandpaper on the floor. Hold your hammerhead on the sandpaper and slide it back and forth until the hammerhead is shiny. That little bit of roughness will help to keep the hammer from sliding off the nails as you smack them in. The galvanized surface of the nails can accumulate on your hammerhead and make it more slippery, so you might want to do this every so often if you notice the hammer is slipping off the nails as you pound them in.

 

[highup]

And don't forget if at all possible bring the plywood panels inside the house and clean them up against the wall to let them acclimate for at least a day. Stack them against more than one wall if you can that will allow air to circulate better around the front and the back of each panel.

 

[highup]

One last thing to mention. If you have any squeaks in your current floor or it doesn't seem to be nailed well enough, add more nails before installing the new plywood.

 

[DarisMulkin]

Another thing to mention is DON"T nail into the joists, it has to do with movement.

 

[madmax64]

I understand that the new plywood has to be staggered and not to line-up the subfloor's original seams. I will use the chalk line (string with colored powder). Can I install new plywood in the opposite direction of subfloor plywoods (well, not that opposite, just turn 90 degrees)??

Should I fill the gaps between the original subfloor plywood with caulk (or do I have to use the cement type) before I install new plywood?

thanks so much.

 

[highup]

With the new plywood covering the gaps, you don't need to fill them. Just float out the low spots.
Keeping the plywood the same direction would add strength, but I don't think you need that since there's already one layer of plywood now.
and your searches you've probably read about not forcing the plywood sheets against each other as you install them a slight gap or barely touching is best. You could use a couple strips of cardboard as spacers to separate each sheet. Cardboard like from a cereal or shoe box would work.
I think when nailing or gluing down solid hardwood, it's recommend to run a skill saw down each plywood seam to create a gap to allow for expansion.
Basically, just don't pry them together tight. A slight gap is better than tight.

 

[madmax64]

I have a special hammer. See attached photograph. Is that what I should use for nailing?

 

[madmax64]

Another thing to mention is DON"T nail into the joists, it has to do with movement.

OK, I will not nail into the joists. The existing plywood subfloor is 3/4" and the new plywood will be a bit more than 1/2". 3/4" + 1/2" = 1 1/4" (1.25"). Do you agree with me that I should use 1 1/4" (1.25") ring shank nails?

 

[madmax64]

With the new plywood covering the gaps, you don't need to fill them. Just float out the low spots.
Keeping the plywood the same direction would add strength, but I don't think you need that since there's already one layer of plywood now.
and your searches you've probably read about not forcing the plywood sheets against each other as you install them a slight gap or barely touching is best. You could use a couple strips of cardboard as spacers to separate each sheet. Cardboard like from a cereal or shoe box would work.
I think when nailing or gluing down solid hardwood, it's recommend to run a skill saw down each plywood seam to create a gap to allow for expansion.
Basically, just don't pry them together tight. A slight gap is better than tight.

Got it. I will use cereal box cardboard for gaps between the new plywood.

"float out the low spots" do you mean I should fill low spots with self-level cement (on the existing plywood subfloors)?

What about the gaps on the existing plywood subfloor? can I use regular caulk to fill them).

Again, thank so much for your help. I am almost ready to begin working on my floor based on your advice and instructions. I am going to the hardware store for prices on 15/32" and 19/32" plywood. (not Home Depot, I am heading to the Lumber supply store where they sell lots of lumber stuff).

 

[highup]

On the existing floor you really don't need to fill any gaps because the new plywood is going to cover over that just fine. When nailing the floor you will get a feel for how well the nails are grabbing. You might get a pound of inch and a quarter and a pound of inch and a half ring shanks and feel which one holds better. That hammer will work it will just put a different type of dent in the wood. It's made for framing. I've never used that type of hammer so I don't know how much different it feels or works than the standard faced hammer.

 

[highup]

If you want to put a little caulking in those gaps maybe to stop air movement or something it wouldn't hurt just don't overfill them.
I mentioned the possibility of one and a half inch nails simply because the ring shanks have about an eighth of an inch of point on them. Like I said when you drive them in you'll find by feel if one works better than another.

 

[DarisMulkin]

DO NOT MISS THE NAIL AND HIT YOUR THUMB WITH THAT HAMMER. It will look like hamburger.

 

[madmax64]

Thank you so much for your help. I have the confidence in doing this project - the right way. Daris, nah I will not miss the nail and hit my thumb with that hammer.

Seriously, I will experiment with two different hammers, one with smooth and another one you see in the picture a few posts ago.