Plastered floorboards?

[Gav74]

We bought a renovated house just over a year ago, and it seemed like they'd done a really good job, then...
We have a room above our bedroom, and when there's someone in there, the floorboards are a bit squeaky, and footsteps are loud. So I decided to pull up the carpets, make sure the boards are properly screwed down and fit a soundproofing underlay - easy job.

To quote my kids "WTAF?"
Obviously plaster isn't designed to be walked on, so it's crumbling, and some of the small bits of floorboard that have been cut have a lot of give when you tread on them.
Now I'm left wondering if I need to pull it all up and redo the floorboards too.
Any advice/suggestions would be welcome, thanks.

 

[Wayners]

Dig up and fit wood.
Guess walls have been fitted over flooring and it can be a big job to get that up and replace fitting more wood supports you stop moment.

 

[JohnD]

Have the boards been cut to run pipes or cables?

 

[Gav74]

Have the boards been cut to run pipes or cables?

I've looked some more and those bits line up with the en-suite's walls downstairs.
Worse than the plaster is that they haven't secured the cut boards either, so there's quite a bit of movement there too, ffs.
There really is no such thing as a quick job is there?

 

[Wayners]

Nope.
Not a quick job.
I'd get the lot up.
Fit more edge support wood and new floor boards if you can't salvage any old boards.

There are companies fixing squeaky floorboards I heard as a problem but yours is poor workmanship

 

[JohnD]

If you're taking up the floor, put struts (noggins) to support all cut edges and joints that are not resting on a joist.

Some will say that chipboard is an inferior material, and 22mm ply is much better.

I am among them.

Screw them down rather than using nails.

If you pack mineral wool between the joists, it will reduce airborne noise such as voices or TV, and also cut heat loss.