Subfloor in the shape of a tub with fiberglass attached? You can even see the imitation marble sitting below it on the backside. It is definitely the reinforced bottom of the original stall.Looks like subfloor to me. 🤷♂️
Okay, I am tearing it all out. I get what you mean that it was the underlayment stuck to the thinset. Yeah, not looking forward to tearing it out but it's on my list this weekend! I'll report back with new pictures soon. Thank you for all of the comments!Agree. Tear everything out. Get a clean slate to work with and post pictures once it is cleaned up. That way we can give better direction. The tub was probably sitting on a bed of squished thinset, which will make taking up the bottom of the tub a real task.
Got it. I reused the old insulation and definitely need more. I will do that and then pick up the new tub and report back. Thank you!Insulate your walls well, and determine if your new tub/shower will need any support under it. Showing us a picture or link of the tub bottom may help. Sometimes you will need to put dollops of thinset under the tub body to add that support. Some come with really adequate support.