issues overboarding a ceiling...!!!

hi everyone,

i'm boarding over my first old wooden lathe and plaster ceiling which has fallen out and is sagging in a few places (i'm not taking it down - i'm boarding over it).. i'm using 6x3 9.5mm boards, and staggering them perpendicular to the joists.. would really really really appreciate your views on a few points!! there are quite a few, and some of them are a bit basic, but i just want to make sure..!

1. what size screws should i use? 38mm enough?
2. how many screws should i use across each board (ie across 3ft)?
3. i've heard that if the screws go through the paper on the board, then it weakens it.. this has happened on quite a few boards i've put up.. should i take them down and put new ones up?
4. The screws which haven't gone through the plasterboard are sticking out a bit - how do you skim over them!??
5. there are gaps between some of the boards i've already put up (some as big as 20mm) - what can i fill them with? bonding plaster?
6. the boards are quite uneven - coat of bonding plaster before the multifinish?
7. er, that's it. but that's enough for now, eh!?

cheers!!
mike

Hi mike.

Personally I would try and use 12mm boards as they wont bend as much, with the shape of the uneven ceiling.

However first remove any screws that are not proud, as they cant be in the joists.
Fill any gaps with bonding.
if any of the boards are damaged/flapping down, then remove and replace.
As you have now put the boards up, im guessing 38mm screws were long enough for the job.
As for the uneveness, will it not plaster/skim out?

If im overboarding with 12.5mm boards i use 50mm dry wall screws minimum. 12.5mm board+12.5mm(ish) old plaster and laths = 25mm
if your using 38 mm screws youve only got 13mm of screw holding in the joist.

bikerm4 said:

if your using 38 mm screws youve only got 13mm of screw holding in the joist.

Click to expand...

Try getting a pair of pliers and pull a screw out that is 13mm in the joist. You'll raise yourself in the air first.