Elliot Coard
Hooks
Hey everyone, this is my first DIY renovation. I'm mechanically inclined (Auto tech by trade), and I pride myself on research, just so I have a general idea and am not completely ignorant to what's going on.
With that being said, My home was built in 1924, I just gutted the bathroom, and decided to remove the the tub to modernize the space, as it's only 5x5. After smashing the cast iron tub to pieces, I noticed that the sub-floor underneath is uneven. 
It looks as if it mortar, or sand even, compacted between wooden beams (Joists? Forgive me for use of incorrect terminology if any). I Plan on using a KBRS tile basin (30x60). Manufacturers specs calls for an application of thinset on plywood to set the base. Am I able to smooth out the existing subfloor by chiseling out the higher pieces? Would I then be able to add a piece of plywood, ensuring it's leveled of course, to set the base? Or would more of the mortar have to be poured to ensure a leveled surface before adding the plywood?
Any insight is greatly appreciated!
Attached are pictures of the subfloor. Don't mind the galvanized piping, as that's getting upgraded too.
It looks as if it mortar, or sand even, compacted between wooden beams (Joists? Forgive me for use of incorrect terminology if any). I Plan on using a KBRS tile basin (30x60). Manufacturers specs calls for an application of thinset on plywood to set the base. Am I able to smooth out the existing subfloor by chiseling out the higher pieces? Would I then be able to add a piece of plywood, ensuring it's leveled of course, to set the base? Or would more of the mortar have to be poured to ensure a leveled surface before adding the plywood?
Attached are pictures of the subfloor. Don't mind the galvanized piping, as that's getting upgraded too.