View Single Post
Unread 04-04-2020, 08:54 AM   #1
Registered User
Join Date: Apr 2020
Posts: 18
Retiling bath, underlayment and plan of attack questions

Hi All, first time posting, and about to tackle my first tile job. Renovating a full bath ~40 s/f. Subfloor is 3/4" plywood (not T&G from what I can see). Existing underlayment is 3/8" plywood, existing ceramic tile laid directly on thinset on the plywood. Some of the original tiles (~8) in main field between vanity and toilet had cracked I assume, because a previous homeowner did a hack replacement job - tiles slightly different variation, plenty of visible lippage and sloppy grout work (can also see in pics that they used a different thinset). The replacement tiles, not surprisingly, cracked as well. Sadly I already started chipping out most of the cracked tiles (easy starting point) before I found this forum, but the pics show at least a couple w/ lippage & cracks in the main field and one under the right side of toilet that's cracked as well.

Ran deflectolator = L/442. (Joists unknown lumber, 9" x 1.5", span of 11.5'. Joist spacing varies, one bay 15.5" OC, another 16.5" and another 16". I split the difference and ran calc w/ 16" OC, faulty logic I'm sure.

Ideally I want to lay a rectangular / fairly large format porcelain tile (undecided on size, maybe 12 x 24 or 6 x 20 maybe). Definitely will not be laying stone. Intend to use Ditra.

1) Any concerns with this plan that jump out?
2) Could the original tiles have cracked simply because tile was laid on plywood rather than on backer or an uncoupling membrane? Original tile job looked ok to my untrained eye (no real visible lippage, grout lines consistent).
3) Should I definitely replace existing underlayment? If so am I ok to replace w/ fresh piece of 3/8" plywood (saw some posts stating exterior grade required, CCX or BCX)? If new underlayment needed I will read posts on placement/screwing requirements.
Note, existing tile is flush with hardwood in adjacent hallway, and unless my math is off I don't think I can keep it that way if I'm using Ditra (thinset above & below)....but I'd like to keep it as low as possible to avoid having trim too much (entry door, bifold door, trim).

Thanks in advance, the info on this forum is a huge help.
Attached Images
whatmemory? is offline   Reply With Quote