New plasterboard ceiling uneven

[Teeth2k]

Hi guys

I have just put up a new ceiling upstairs using 12.5 plasterboard but what I've noticed is on the on the joins there is about a 8-10 mm height difference which has been caused by a slightly twisted loft string joist in one corner.

Can anyone throw suggestions on what I could do to rectify this

Regards

 

[stevethespreader]

Take the board down and pack out the difference

 

[NickB_99]

As Steve.
8-10mm too much to adjust for with finish plaster.