Plasterboard ceiling question

[tea-not-coffee]

Hello all,
I need to fit new plasterboards to a ceiling. The old ceiling has been removed so I just have exposed joists. I have read a lot of useful stuff in the forums here but I still have one unanswered question. Having offered a straight edge against the underside of the joists it seems that they are slightly uneven - I would estimate that there is a variance of around 5-10mm between the highest and the lowest. Is this acceptable or do I need to level out the joists with shims in some way before fixing the new boards?
Cheers,
tnc

 

[-dj-]

i shouldn't worry about that much varience, however if you are a perfectionist then throw a few shims up.
board with 12.5 and you should be able to lose it.

dj.

 

[tea-not-coffee]

Ok, I will give it a go.
Cheers.

 

[madsey]

ARE YOU MAD !!!!!

 

[-dj-]

yeah, why??

 

[masona]

I would estimate that there is a variance of around 5-10mm between the highest and the lowest.

I would try and get it level as much as you can because 10mm is rather a big gap, you may find when using plasterboard nails or screws it will pull into the plasterboards half way giving you more problem.

 

[masterbuilder]

To answer your question about the ceiling, 10-15mm is acceptable and not noticeable, any more than this and you should even it out by cutting 50mm strips of plasterboard to pack it out where needed, feather it off with a stanley knife where needed and use longer screws where you've packed it out when boarding

 

[legs-akimbo]

Once you have the boards in place if there are slacks (hollows) in the boards then by placing a straight edge to the ceiling they will be visible. make pencil marks where they are and dubb them out with bonding and rule them out flush with the straight edge. As it sets, smooth it out with your trowell, when its gone off enough simply skim the ceiling as normal and you will have it perfect, to aid a flash set (quicker cure) on the bonding throw in a trowell full or two of hydrated lime or even cement.