Complete rebuild 75 year old bathroom

[BillArlVA]

I've read a bunch a the posts and with the amount of info, I bet someone could point me at a post that answers my question directly, but I haven't found it, so here goes...
I'm completely rebuilding a 75 yo 2nd floor bathroom (except leaving the cast iron good condition tub in place). This is the 5th bath I've redone in this house, so I've had some experience (learned hard way) about making things square and level. The room is completely stripped to the studs and all the old piping/electrical is out. The joists are 2x10 16"oc. The old sub floor was 4 inches of dry concrete with about 2 inches of hard concrete poured between the joists (on top of planks about 1/2 way down the joists) - it's all gone now - what a nightmare! The top 1 1/2 to 2 inches of each joist was peaked (looks like with an axe) to keep the overlying cement from cracking along the joists. In addition, there are many holes through the joists for 2" drain pipes and many notchings along the tops and bottoms for water supply lines. The area to be tiled is about 66" x 63" The max joist span between structural support is 8'.
My plan is to sister all the joists with 2x6 and put some additional 2x6 blocking for stiffening. In the past, I've then used 3/4 ply and 1/2 ply followed by 1/4 cement board (with thinset between the top ply and the cement board) as a subfloor prior to ceramic tile. Am I on target?
Thanks!

[John Bridge]

Hi Bill, Welcome to the forum.

I'd say you're on target. I would have left the old mud bed in place. It held up a long time.

I'll add you to the list of threads for Bob Campbell, our engineer, to look at when he comes in tonight or in the morning.

[BillArlVA]

Thanks! I wanted to leave the mud subfloor, but the old galvanized pipes were in it and if I was doing this much work, I figured it was time to replace the galvanized, too.

[bbcamp]

Your plan looks good to me!