Plasterboard question - how much board movement along joins is OK

[flyingspark9876]

Hi The problem I have is ceiling cracks (straight lines mainly along plasterboard joins). The ceiling is artex on plaster skim on 12.5mm plasterboard. I know the previous owner had a water leak from above and an insurance bodge job was unfortunately made. I'm considering getting the entire ceiling skimmed flat professionally but am worried that the cracks will reappear. I'm not sure if they are caused by after effects of water damage or because of the slight updown movement between the boards. The joins were all taped with paper tape. This was stuck down well with no cracks, but the plaster and artex above has cracked. Before I spend the next god knows how many weekends cutting out the old boards, putting in noggins,battens, new boards,.... I would really like to know * how much movement is acceptable for a plasterer to reskim over the lot, withstand the movement, and get no more cracks. The movement is 1mm updown at worst, and 0.5mm in other places.

• Also I am thinking of using scrim mesh tape for the joins as opposed to paper tape. Will this make the join stronger and less crack prone than the paper tape.

• If I put in some new plasterboard screws to try to resecure the existing boards (currently nailed) or bang down existing nails some more - worth trying?

• Do I need noggins behind the joins between joists if the joist gap is 15 inches.

• The joists themselves are 46mm thick (just under 2 inches), is this wide enough to take 2 joining pieces of plasterboard down the centre or should I fix a batten with the join line along the joist / batten edge.

• If I am only putting in short lengths of board is it still necessary to have the good tapered non cut edge running perpendicular to the joists. Can I go along the joists.

• When joining the cut plasterboard edges (ie non tapered), should I try and make a taper by rubbing away some of the plaster and surface paper in order to strengthen the join.

• What is best to fill the join so that cracks dont appear (as well as scrim/tape)- board fininsh plaster, joint filler, other

• Whats the best way for cutting out the old boards gently and cleanly so I dont make new cracks. A padsaw seems a bit rough, stanley knife seems awkward, small old tenon saw?

Sorry - bit long on questions at the moment and short on answers. Its the movement question at the top of the list

Thanks for any advice, nick

[Phil L]

I don't understand this part, 'the plaster and artex above'?

None, the boards should have been screwed, but this is of little use now.

too much...there should be no movement at all at the joints and maybe 0.5 elsewhere

Scrim shouldhave been used in the first instance, paper is only of any use when artexing straight onto P-boards or when they aren't getting plastered, plaster needs scrim

Yes, get as many screws as yuou can in along the cracks, but if they don't hit timber, take them out, then apply scrim along each crack.

Alledgedly, but I've never bothered and never had any serious (highly visible) cracking.

Are you taking the ceiling down and starting again?

You can go any way you like, so long as the joints are tight and get scrimmed prior to plastering.

No

Nothing, the joints should be so tight that a cig paper cannot be inserted between them!

If you are taking down parts of the ceiling and getting a plasterer in, you'd be as well taking the whole lot down and starting from scratch, plasterers prefer whole ceilings rather than patching up and the entire ceiling would probably be cheaper and a better job in the long run than aqtempting repair.

[Guy King]

The message from [e-mail] contains these words:

No joins should run in the same direction as the joists except those on the joists themselves. Joints running from joist to joist shouldn't need supporting but if you've got trouble then I'd noggin everything.

[flyingspark9876]

Thanks a lot. Thats clarified things up a lot. I should have added that the movement doesnt occur ordinarily (ie people in room above), but only when I'm applying thumb pressure upwards on the board myself. I guess the movement would still sooner/later cause cracks if it isnt fixed properly.

[Yes that is my mistake in the original post - paper tape witb cracked plaster and artex over not underneath]

thanks, nick