Plasterboarding over lathe ceiling and then skimming

[Bedrock9]

Hi, tried to find similar threads but they all seem to be about jointing and filling!

I have some old ceilings with massive cracks and intend to plasterboard over them and then skim myself. The questions I need to answer though are;

1. It is correct I should use square edge boards when skimming over too?
2. It is advisable to leave a small gap of a few mills between each board to get some of the finish in between them (sure I read this as a way to prevent cracking between boards)?
3. Should I tape the gaps with the mesh scrim tape, or paper tape, or none at all?
4. The how too's I have read suggest nogins between joists to fix screws at the board edges between joists. This isn't going to be possible without removing the old lathe and plaster which I would prefer to avoid. Is this really necessary from experience with 12.5mm Boards?

Thanks!

 

[Happyplumber]

If you want a proper job ,then get a spade and good quality mask and smash all of that lathe n plaster off ,especially if it is loose and cracking

Then fix the new boards straight to the joists,there is no need for leaving a gap between boards,multi finish has no structural strength and is not there to prevent cracking .It is there purely for a cosmetic finish!

Make sure to use dry-wall screws and use proper plasterboard tape for all joints

Doing a quick lash up will take the same amount of time and will cause you no end of headaches after .

Do the job once and do it right

 

[PrenticeBoyofDerry]

1. It is correct I should use square edge boards when skimming over too?

It is not incorrect, but some do use taper edge to facilitate the tape.

2. It is advisable to leave a small gap of a few mills between each board to get some of the finish in between them (sure I read this as a way to prevent cracking between boards)?

Back in the day it was common practice but not doing has never caused me an issue

3. Should I tape the gaps with the mesh scrim tape, or paper tape, or none at all?

Self adhesive, nylon mesh.

4. The how too's I have read suggest nogins between joists to fix screws at the board edges between joists. This isn't going to be possible without removing the old lathe and plaster which I would prefer to avoid. Is this really necessary from experience with 12.5mm Boards?

That would depend on the distance between joists, but if this is not possible then it is not possible, you may catch the odd lathe, which can only help.
But I would personally rip the lot down, but it makes one hell of a mess, so plenty rubble bags and don't forget gloves, dust mask, goggles, safety boots etc or consider to battening out. I have in the past when unable to screw up to timbers between joist, put a dab of adhesive in the gap to help prevent sagging, but you are reliant on the surface above.

 

[OwainDIYer]

if you batten the ceiling you can make sure you have good fixings through the lath and plaster to the joists, and put battens where the ends of plasterboards will be.

Also take into account any variation or off-level of the existing ceiling etc

 

[Bedrock9]

Cheers guys.. inclined to go for the bodgers option though and just hope it's ok, taken enough sacks of crap to the tip already!