Mortar piles: crunching sound in one area.

[Makemenuconfig]

One of these days I'll be done posting bathtub questions...sorry guys.. This is my first time doing this and I appreciate the advice.

I set the tub about a month ago in a sand mortar mix using the mortar pile method I read about here. I put about 5 or 6 piles and avoided the foam feet areas. There were some areas around the perimeter with voids where I shoved extra mortar in with a stick then built up around the perimeter a bit. I was careful not to touch the tub for a few days.

I was walking around in it yesterday and noticed an almost crunching or squeaking sound in a specific area. It isn't too loud, but definitely noticeable. Investigating more I decided to push hard with my thumb in a methodical pattern and put tiny pieces of tape where I heard the noise so I could see the affected area. Attaching a photo of this. I notice the acrylic flexing a little when I press hard. The noise is most noticeable when rocking firmly from foot to foot in and out of the affected area. Made a video, most accurate representation of sound around 28 seconds.

I assume somehow the mortar isn't quite touching the tub in this area or there is some amount of a void. Is this going to be a problem long term that would lead to premature destruction of the tub? It seems strange that I would have gotten perfect mortar coverage on the thick side but not the thin side. What are my options to fix this?

I can access the tub from the drain side and could cut into my freshly mudded drywall on the back side of the tub if needed. There would be mortar all the way around the base though, so I'd have to chip that away to have any hope of getting anything in there. And then what would I get in there; a shim? Though I have started waterproofing, I have not tiled yet. As much as I don't want to re-do work I would pull the tub and either re-set or install a new one if that was necessary.

 

[Reach4]

How is the access from below? Cut a hole in the flooring, and shove mortar in around the top of the hole?

 

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[Makemenuconfig]

How is the access from below? Cut a hole in the flooring, and shove mortar in around the top of the hole?

Not great; we have 2" tongue and groove solid pine subfloors which are hard to cut through gracefully. But to be clear, I believe there is mortar under this area just not quite enough to fully touch the bottom of the tub. Like it wasn't quite built up enough.

 

[Reach4]

Not great; we have 2" tongue and groove solid pine subfloors which are hard to cut through gracefully. But to be clear, I believe there is mortar under this area just not quite enough to fully touch the bottom of the tub. Like it wasn't quite built up enough.

Your piles should have been big enough to squish, which you knew. So can you get more mortar in now? If there is an easier way, go for it.

If you cut through the subfloor with a hole saw, you would need to remove the pilot drill once started. You would need to ensure that your hole saw does not cut the tub.