Hello...this is my first post here. I have read many threads (enough to think I have a pointed question that I didn't see answered anywhere else).
Background first (the usual suspect questions
I have a kitchen I am remodeling from a 1941 home. The sub-flooring is 1" x 8" pine (seemingly) board planks run at 45 degree of joists installed with nails. They aren't T&G and do have approx. 1/8" gap between them. They were in pretty good condition, those that weren't we replaced and all loose nails either renailed or removed and the nail replaced. The joists are 2 x 10 anywhere between 14"-16" OC.
Using the deflecto gauge at johnbridge.com it looks like I am boarderline for tile for floor deflection. Sistering the joists isn't an option due to lots of water lines, electrical and duct; so strength is something I need to gain where possible. Also my goal is to have the kitchen (space approx. 11' x 13') floor level with the adjoining dining room & hallway hardwood floors. This means I have 3/4" on top of the sub-flooring to work with. My tile is 3/8" (calculated factoring in 1/8" for thin set mortar), leaving me with 3/8" left for an underlayment material.
I did go out and purchase "construction" grade 3/8" plywood for the underlayment, but after reading here realized the quality of that construction grade wasn't very good (DD exposure 1)....so obviously that is going back....
From what I have read here are my options:
1) Not tile at all.....my wife would put me out of the house, so not an option
2) Continue with current plan to lay 3/8" plywood of at least quality of CD but preferably AC, exposure 1 exterior plywood screwed to the sub-flooring and then lay the tile into thin set directly on the plywood (I know not the favored approach here) but this would give me 1 3/8" flooring base for the tile for strength purposes
3) Lay 3/8" concrete backer board screwed directly with concrete board screws to the sub-flooring and then lay tile with thin set mortar. Question I have is if I use a backer board...should I count this in the strength of my flooring thickness...so would I consider having the 1" sub-florring + 3/8" concrete board for a total of 1 3/8" total flooring for the tile; or since I keep reading that backer board isn't for strength, do I not factor it into my calcuation for total flooring under the tile; which would leave me at only 1" of flooring and below the minimum?
4) Lay 1/4" CD or AC, exposure 1 exterior plywood screwed to the sub-flooring. This would give me 1 1/4" total flooring for stability. Then lay 1/8" Ditra with modified thinset to provide a tile friendly surface. Lastly, lay with unmodified thin set my ceramic tile?
Also, two other questions; when we pulled up the original 3/4" plywood underlayment and vinyl flooring, there was a thin, almost like a backing paper, layer between the planked sub-flooring and the underlayment. We didn't know what function this served? Just to keep debris from falling in to the basement level? My father thought a good idea might be to lay a thin moisture barrier (like a 2 MIL plastic sheathing material) just to reduce the risk of moisture from the basement (partially finished and partially unfinished, but does have finished plaster ceilings everywhere. Also it does get some minor moisture from exterior) getting into the underlayment. Is this a good idea? Maybe a good idea if using plywood but not necessary if using backer board?
Finally, the floor is pretty good on being flat, but there is a sligth downward slope from front to back of the kitchen of approx 1". It doesn't seem to be very noticable and it sounds like if the floor is flat we shouldn't worry about the slope? I looked like when the floor was originally installed they used asphalt (shingle like) strips about 3" wide that they laid under teh underlayment where the joists are to adjust the slope of the flooring. After my reading I am thinking this wouldn't be a good idea to re-use this approach as asphalt shingles could be more of a "spongy" material to further create variation in the floor plane; but I wanted to get the thoughts of the experts?
Thanks in advance for the advise and sorry for the long post