Hi,

I am prepping to install 3 1/4" strip maple. The subfloor is 5/8 OSB. I plan to lay 3/8 plywood underlay over the OSB. I have two questions, and would appreciate any help: 1) What should I use to nail the underlay? I have some 1 1/4" ring shank flooring nails, but I have read that the nails should not protrude through the subfloor. 2) I do have a compressor, and would consider using a nailer, as I have several hundred square feet to cover. If I chose to buy a nailer, what model and which nails would you recommend? thanks.

Stapling works better than nailing. You can also screw it down. But I staple because it's fast and cheap but still works very well for plywood up to 1/2" thick. You could rent a stapler for the day. Get a construction type with 15 to 16 gauge staples and about 1/2" wide and legs that are 1.25" long. Staple 4" on perimeter and 6" in the field. You can glue as well using construction adhesive.

Thanks Gary. Is it acceptable to use 1 1/4" staples when the underlay and subfloor measure 1"? Would it be preferable to use a smaller staple?

I also have another problem that I have not yet resolved. One of the joists seems to be higher than the rest, and on one side of this joist, the floor slopes off about 3/8" - 1/2" to the wall ( it is about 2 - 2 1/2' from the joist to the wall). So, I have a hump and a depression. What would you do in this case? Thanks.

Whenever I do a sub floor repair I floor the new sub floor to the joists after all the blocking is done, along with screes or if a large sub floor use my Senco nailer. I feel it helps in the squeaks department. If I was installing underlayment prior to a new floor I'd use glue and 1/2 crown staples as Gary recommended.

Michael