Hello all! I am new here and seeking advice about the hardwood floor on my second floor. My wife and I purchased the 20 year old home about two years ago and was built by the people we bought it from, mostly by themselves I believe. There is 3/4” ash tongue and groove boards on top of what appears to be roofing felt on top of 3/4” pine tongue and groove boards. The reason for that I understand is because the joists are on 32 inch centers (visible from the first floor). The problem I have is varying size gaps between many of the ash boards. I don’t know if this was lousy workmanship or if things have just moved. I have cut the tongue off of one row and started pulling the ash floor boards up. My plan is to reinstall them tightly and fasten them with 18 gauge pins. Are these pins heavy enough? I see the ash was initially stapled about every 16” or so with much heavier 1/2” staples. I am finding out this is quite an undertaking (about 400 square feet) and I’m wondering if there’s a better way to do it or is this the way to go. The floor has not been finished (stained/top coated) just FYI. Any advice would be much appreciated and thank you in advance for any help.

16 gauge nails or staples are better than 18 gauge, but 18 gauge powercleats are used for 3/4 in TG. They are flat fasteners called P nails and have barbed edges that hold. A special nailing gun that holds the fasteners at the right angle is used for the 18 gauge powercleats. Nail every 10-12 inches and also near the ends of boards.
If you floor has been sanded, the sanding process will make the thickness different for boards depending on where they were located, so you will need to sand the floor again unless you manage to keep the boards in sequence when you fasten them down, again.
Ash is a pretty stable wood so once it has acclimated it will not expand and contract from humidity as much as other wood types.

Thank you for the advice. I will look for the flooring gun and powercleats you mention. I have been keeping the boards in the same position they came from and will continue to do so in view of your comments about having to sand the floor again if not doing so. Great advice.