hairline cracks and peeling paint

[jaylockwood1978]

Hi, novice here so please be gentle!
We're decorating our bathroom but before we start there are some long hairline cracks to repair. Ones probably the width of a penny, other you couldn't even get a Stanley blade in.
I scraped along the really thin one like I was told, to then eventually use plasterboard jointing tape over and then cover in plaster compound (got a readimix one from Wickes).

Major problem I'm having is that once I scrape along the crack, the paint peels, and is coming off with very little effort to lift it. Guessing moisture has gotten in. Bathroom was decorated prior to us moving in.

Any ideas what to do? Is my filling method a rubbish one? And what to do about the peeling paint?

I've attached some photos, the first shows the extent of the amount of paint that has come away very easily. I haven't dug at it it's just peeled in large whole pieces.
Second photo is the crack I scraped st with a blunt screwdriver.
3. The original size of the crack after paint has come off.

Thank you in advance

 

[jaylockwood1978]

In addition, just took some more off and there is writing underneath (must have been the builders or someone) that is perfectly readable. I'm even more confused now as that should have been painted over?

 

[Robbie uk]

If the emulsion is coming off that easily then you need to keep going and take it all off. Its either never had a mist coat first or it may have had a coat of PVA prior to being emulsioned. PVA should never be used where your going to paint. The cracks need raking out and filling with a powdered filler not a ready mixed as this usually sets to hard to rub down smooth. Paint over the filler with a thinned coat of emulsion to seal the filler and let it dry prior to putting on further coats.

 

[jaylockwood1978]

Thanks Robbie,

I've took off all the easy paint do far, is it ok to leave it at this point or should I scrape away and clear the whole wall? Don't want to scar the plaster and create loads of other problems.
If I don't have to scrape the whole wall, should I then fill the cracks like you said, the mist coat the bare section, and then put final coats over the whole wall?

So annoyed they botched it like this!!

 

[Robbie uk]

Try and get as much off as you can. Any that's left, sand the edges to feather them off and apply a mist coat. When dry, fill everything that needs it, the cracks, the old paint edges that's left etc. Use a powdered filler not ready mixed. Tourpret or similar. Gently sand down and apply further coats checking the filling between coats.

 

[Chri5]

Tile the bathroom floor to ceiling