Ah yeah, you're right. Mastic in a bathroom is bad enough, but on a ceiling? That's crazy.

Did you notice that it's the backer board itself that's sagging, not the tiles? OP is going to have to figure out how to secure that to the joist(s) and IMO any kind of adhesive would be dodgy. I'd want mechanical fasteners involved in that fix personally.

Stanley Bailey #4, 5 or 6 hand plane. Buy one used, sell it when you're done for the same price. You'll have to learn how to sharpen properly to get good use out of it though.

I'm not sure, kind of a weird scenario. An oscillating tool would work but it'd be slow. A biscuit joiner might actually work well, although it's not meant for that purpose. Not sure how the blade or motor would stand up to that kind of usage.

Actually he's quite incorrect in one of his points, which is another example of something Reddit is good at- misinformation. Your house does not expand or contract around your floor. It's the floor that changes size due to temperature changes.

That said he's right that cutting in an expansion gap is a good solution, just not for the reason he gives.

>It's the house that expands and contracts around the floating floor. The structure of the house is wood.

This isn't actually the case. Wood only expands/contracts perpendicular to its grain. Your house is framed such that it's effectively stabilized from such movement.

Skimcoating an entire bathroom is a job for pros. Trying to do it yourself will be very time intensive. Doable, but long, frustrating and extremely dusty.

Yes, that's a good point. Wasn't thinking about exterior doors.

Really need pics. Use Imgur, put the link in as text.

Good info. I'll just add that inswing and outswing are simply orientation. A right handed door is a right handed door - in or out swing is just how you mount it. Important for the build spec, but irrelevant to ordering.

There's really no way to answer without seeing the cabinet in place. Context matters.

You use mold resistant drywall (it's green) and otherwise patch it normally. Then prime and paint before using the shower.

The rest of your drywall in the area above the surround is just regular drywall, so no need to get crazy here unless the rest of your ceiling has moisture issues.

Also worth noting that the time is time to recoat, not time to sand. Sanding can be hours or over night still, depending on conditions.

I think you're looking for the wrong type of solution here. The proper fix for a railing is to remove some of the plaster, add additional wood framing to create a strong anchor point, then repair the plaster.