do i leave a 3mm gap between sheets of square edged plaster board on my ceiling before using tape and then skimming?
this was advised in he coliins DIY manual.....

thanks again

I have never been told to leave gaps, quite the opposite, get the boards as tight as possible IMHO.

You will still need to scrim joints and any areas where there is a 3mm gap wil be sorted with the scrim and skim but i wouldn't leave gaps on purpose.

Unless im wrong,,, all my ceilings are fine............

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You'll never know if you don't ask.......or try and then balls it up and learn by the last balls up, but still...best ask!