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As an introduction, I'm a DIY home owner who has gutted the bathroom in a house built in 1980 due to a burst water pipe. I had a professional water mitigation company remove the damage so I'm sure all of the affected material is now gone. I have decided to put large format tile on the floor in the bathroom to start and have a few questions regarding the very conflicting advice that I have found in forums, on YouTube, and in asking questions of local flooring company employees.

I have 3/4" (19.05mm) tongue and groove subfloor sitting on 12" on center 2"x8" floor joists. The bathroom is 60sqft. I have purchased a large format porcelain tile (insert size here) to be installed on the floor of the bathroom. In my "research", I have found some that argue the layers on top of this subfloor should be as follows:

  • 3/4" subfloor (existing)
  • 1/2" plywood to be installed directly on top of the 3/4" subfloor via screwing it down in the field (from what I understand this is putting the screws into the subfloor in between the floor joists)
  • Caulk / Self expanding foam and self-leveling floor primer
  • Self-leveling compound as parts of the floor are slightly uneven and need to be rectified
  • Thinset
  • 1/4" - 1/2" Concrete backer board screwed down to the second layer of plywood
  • Thinset
  • Schluter Ditra uncoupling membrane
  • Thinset
  • Tile
  • Grout
Obviously my first concern is that this will ultimately make the transition into the bedroom and hallway that share an entrance with the bathroom a cliff and therefore a bear to make it not seem like you are stepping up into the bathroom.

My second concern is that many sources say, "Oh, it should be fine to just screw (no thinset or https://www.tilersforums.com/forums/tile-adhesive/) concrete backer board to the 3/4" subfloor" once it is primed and self-leveled. I don't want to be ripping this tile out in a month, or even a year because of cracked tiles and grout, because it "should be fine". I've read that large format tile offers less play than smaller tiles and therefore the substrate it bonds to must be a fairly stable material.

Next, we removed the very old fiberglass tub insert and shower surround and plan to install a fiberglass tub insert, then prep and tile the new surround after I've replaced all the plumbing that needs replacing. At what level of the flooring above should I install the new tub?

Thank you for your time.
 
J

Jpvvpj

Durock or cement board should always be thinseted or use mastic to the plywood.. then screw it down every 8 to 10 inches.. if you don't there will be a small amount of movement in-between the screws and this will make your floor fail.. make your thinset where it is pourable then use 1/4 inch notch to set it in place.. we do a lot of large format porcelain and you really gotta have super flat floor the larger you go with tiles or panels .. floor hight becomes a problem when you have an uneven floor but you gotta have it flat.. we don't use extra plywood and all of that we float the floor with sand and Portland cement,, not something that a DIY should attempt.. depending on how bad or not so bad the floor is you could use 1/4 inch durock then prime and use self leveling to fill in the low spots. Hard to really give advice without seeing what your dealing with but this would keep your floor as low as possible.. as far as the tub goes you can install it before any flooring work happens. Then tile up to the tub with floor tile..
 
T

Tony R

Response inline below:

3/4" subfloor (existing) (yes)
1/2" plywood to be installed directly on top of the 3/4" subfloor via screwing it down in the field (from what I understand this is putting the screws into the subfloor in between the floor joists) (1/4 in - 1/2 - take total height of floor into consideration)
Caulk / Self expanding foam and self-leveling floor primer (No)
Self-leveling compound as parts of the floor are slightly uneven and need to be rectified ( sure, but consider one of the less labor and mess intensive systems)
Thinset
1/4" - 1/2" Concrete backer board screwed down to the second layer of plywood (No)
Thinset (Yes)
Schluter Ditra uncoupling membrane for a floating floor not applicable here)
Thinset (already applied)
Tile (Yes)
Grout (Yes)

Add: Grout sealer and tile sealer if needed.
 
T

Tony R

Response inline below:

3/4" subfloor (existing) (yes)
1/2" plywood to be installed directly on top of the 3/4" subfloor via screwing it down in the field (from what I understand this is putting the screws into the subfloor in between the floor joists) (1/4 in - 1/2 - take total height of floor into consideration)
Caulk / Self expanding foam and self-leveling floor primer (No)
Self-leveling compound as parts of the floor are slightly uneven and need to be rectified ( sure, but consider one of the less labor and mess intensive systems)
Thinset
1/4" - 1/2" Concrete backer board screwed down to the second layer of plywood (No)
Thinset (Yes)
Schluter Ditra uncoupling membrane for a floating floor not applicable here)
Thinset (already applied)
Tile (Yes)
Grout (Yes)

Add: Grout sealer and tile sealer if needed.

Disregard, incorrect reply towards Schluter Ditra uncoupling membrane.
 

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