Underlayment Help

[shubox56]

Hi Guys,

New to site and need help. May have several questions in the days ahead.

Question 1: I recently had a carpenter remove compromised subflooring under 2 toilets, he added a significant amount of bracing and replaced the .75" plywood subfloor. The .25" underlayment was left to me which leads to my question(s). With the underlayment cut and ready for install, I'm considering zinc coated screws since I don't have an air compressor or staple gun. I've read that if nails or screws are used to NOT penetrate the bottom side of the subfloor which leaves me questioning what screw size would be best? All screws designed for underlayment seem to be 1.25" or longer which would blow through my 1" sub/underlayment combo. Even a 1" screw will once countersunk slightly below the surface and filled will penetrate. Wouldn't a .75" screw be troublesome long-term? Holding issues? And besides the length, what # screw would be best for .25" underlayment? #6? #7? #8?

Any screw recommendation or OTHER tips? I certainly want to get this right the first time. And EVERYTHING I've been reading also says to avoid gluing the underlayment to the subfloor.

Once I know what fastener would be best, a screw type, size and supplier, then I'll have to figure out the spacing.

Many thanks for my first round of questions!

 

[Mark Brown]

When using nails or screws you are going to penatrate the subfloor entirely. This is not only ok, it is common and an approved installation method as listed under the American plywood associations recommended installation for underlayment. Using screws I would not suggest, neither would the APA however as a last resort, keep them flush with the top of the wood and fill the heads and you are probably gonna be ok

 

[shubox56]

Hi Mark,

Thanks for the quick reply. Would ring shank nails be a better choice? An APA approved method? 1" nail? A nail size in mind?

 

[Commercial Floor Rep]

I used ring shank Maze (brand) nails for small jobs rather than drag out the compressor without issue. I'd probably use 3/4" if your subfloor thickness is a total of 1". I like those nails over the standard galvanized nails at the box stores because they are double hot-dipped with zinc and way less likely to cause any rust issues. The ones the boxes sell are typically electro-galvanized and have a near transparent coating of zinc which can be easily scratched off when hammering them or even from rubbing against each other in the box.

I don't like screws because most of them have a dead space at the top that once you hit it can prevent the screw from properly seating and leaving them proud. I've seen guys run into that on a job and literally beat them the rest of the way in with a hammer. This obviously defeats the purpose and completely destroys the holding power of the fastener.

 

[shubox56]

Hi Commercial Floor Rep,

I see these on there site: Underlayment & Plywood nails | Maze Nails

Underlayment nails with the shortest being 1". My floor total width being 1".

Right track? Or should I rent a compressor?

 

[Commercial Floor Rep]

Yep! I think you'll be fine.

 

[shubox56]

Yep! I think you'll be fine.

Nice! Any recommended spacing for this nail along edges and in the field?

 

[Mark Brown]

Go get some nails, something that small is hardly worth renting tools for unless you are lazier that I am in which case kudos to you. In all honesty, penetrating the subfloor with nails is a 0 issue as in it does not exist. These are not my words, they are straight from the APA. I dont know anything but i do know how to read smart peoples opinion on things
Last i checked staple fastener length was the be 85% of the subfloor plus the depth of the underlayment, but it changes from time to time.

Nail spacing is 4 inches in the field and 1.5 inches along the edge set back 0.5 inches. This is true up until 3/8 underlay, possibly 1/4 then the spacing gets wider.

 

[Commercial Floor Rep]

Mark types faster than me.

 

[Mark Brown]

I just had a head start. LOL
I am willing to bet you got me beat, i am a 3.5 finger typer with my dominant hand doing mostly single finger floating and my other hand using 2 fingers. The half a finger is for the space bar

 

[Commercial Floor Rep]

I swear to Budda, best class I ever took in high school was typing. I learned how to touch type and also use an adding (business) calculator without looking. I use those two skills everyday. My problem is that I can type faster than I think. So, I have to constantly edit and re-read before I hit post.

 

[Mark Brown]

Oh man dont get me started on typing faster than I can think.... you might have noticed over the years. I dont edit so well lol

 

[shubox56]

Go get some nails, something that small is hardly worth renting tools for unless you are lazier that I am in which case kudos to you. In all honesty, penetrating the subfloor with nails is a 0 issue as in it does not exist. These are not my words, they are straight from the APA. I dont know anything but i do know how to read smart peoples opinion on things
Last i checked staple fastener length was the be 85% of the subfloor plus the depth of the underlayment, but it changes from time to time.

Nail spacing is 4 inches in the field and 1.5 inches along the edge set back 0.5 inches. This is true up until 3/8 underlay, possibly 1/4 then the spacing gets wider.

I really appreciate all the responses. I have a tendency to overthink things yet STILL get it wrong. YIKES!

So if I'm reading you right, 1/2" from the edge with 1 1/2" spacing. Much tighter than I would have guessed. Glad I asked.

 

[shubox56]

I swear to Budda, best class I ever took in high school was typing. I learned how to touch type and also use an adding (business) calculator without looking. I use those two skills everyday. My problem is that I can type faster than I think. So, I have to constantly edit and re-read before I hit post.

Love it! A sense of humor is all that we have these days to survive, it seems.

 

[Commercial Floor Rep]

Mark and I are mates (Canadian for friend). He's liked me every since I told him that people from Indiana are like "Canadian Hillbillies". He's got a warped since of humor. Don't try to figure it out though. I've been in therapy for nearly two years already!

On a serious note....

This link has some really good visuals on the pattern and "order" you should follow when installing underlayment. Scroll down a bit. You should start in a corner and work out like they show to prevent putting lift in the middle of the panel. Many people who've never done it start and do the edges all the way around and then fill in the middle. That can cause issues.

Here's the link:

Plywood Flooring Underlayment Installation Instructions

 

[Commercial Floor Rep]

P.S. follow Mark's nailing schedule recommendations. The one's that the site lists are more for stapling. Mark's are better.

 

[shubox56]

Here's one of the bathrooms with underlayment. I cut the 1/4 plywood underlayment yesterday but WISELY waited.

I'm am questioning the tight subfloor joint spacing, though. I'm hoping it's not an issue for a small patch?

 

[shubox56]

I'll have to do a little repair on the edges that splinted. Not the best of blade to get the job done. :-(

I was shocked to get the angles and flange hole close the first time out. The other bathroom underlayment is a much easier cut.

 

[Mark Brown]

Question, what are the weights doing on the subfloor? Just holding it down??
I wouldn't worry two licks about your subfloor spacing. If there is space at all it is fantastic. IF there isn't run a circular saw through it if you are worried. I wont lie, more than once in my career i have jumped my fat arse on a piece of underlayment or subfloor to get it to seat. THIS IS NOT THE CORRECT WAY but most the time i do not worry too much about it and life goes on. By definition it should have a 1/8 gap.
Ever work with tongue and groove ply? Ever wonder why you cannot get it tight together? its because you are not supposed to!!

 

[shubox56]

Hey Mark,

Yep, the weights which are not there now we're used to help it lay flat for the pic.

Thanks for the information. It's good to know that the gap will likely not be an issue. I've read more than once about floors buckling, so felt compelled to ask. There are a few spots where it's wood on wood contact which likely resulted in him doing something similar to what you mentioned. In those few spots, I may try to open up the gap.