How to replace rotted ceiling laths with metal lath

[Gary111]

Hi my laths have rotted and the ceiling is not supported on the area around 2/3 of the bath.

I have the floor boards up.

Can I replace them with "metal lath"
Nailed from above to the bottom edges of the joists?

Then pour thin bonding coat, or plaster of Paris over from the top?

It seems like it might be a bit saggy?
Also I have some galvanised site with squares around 1cm, it's quite stiff, is there any reason I can't use that rather than the "metal lath"


Thanks

 

[JohnD]

Start by supporting the ceiling from underneath with large propped boards

Remove broken nibs and other rubbish, especially anything lodged between the joists or laths and the plaster

Vacuum it clean

Jack up the props so the boards press the plaster flat and smooth against the timber

Throw away your hammer and nails and use a cordless drill to galvanised-screw the lathing onto the joists, after folding it into trays, with the flat resting on the plaster. Hammering near old plaster cracks it and makes it fall down.

Mix small amounts of pourable fine plaster and pour it, one bay at time, onto the ceiling so it puddles on the clean old plaster and submerges the lathing

Leave for a day or more to set and dry

Loosen the props and lower the boards

Where the old ceiling has cracks or holes, use plastic sheeting or clingfilm on the board to prevent the new plaster sticking to it.



Or

Pull down the old ceiling, board and skim it. To get equivalent soundproofing, you will need two layers of plasterboard plus skim.

 

[Diver Fred]

Pull down the old ceiling, board and skim it. To get equivalent soundproofing, you will need two layers of plasterboard and skim

This - above.

But you need to find out why the laths have rotted! Is it damp or woodworm? Either way the cause needs finding and resolving.

 

[JohnD]

around 2/3 of the bath.

Looks like damp.

Leak? Or persistent splashing?

 

[Gary111]

Thanks for your detailed reply, is it plaster of Paris that I need to get or is there some other pourable fine plaster?

Just checking that I don't need to add thinned pva to the old plaster before pouring?

I also remembered that I have some thinnish gauge builders band, can I use that instead of the metal lath?

Thanks again for your help.

 

[JohnD]

I used hard finish plaster (as used for skim). It can be mixed to a pouring consistency. You must finish pouring and spreading it before it starts to stiffen. I don't know if there's something better. Plaster of Paris is not retarded so has a short working time.

The old plaster will have a ridged and rough surface, I don't think it needs PVA but you can if you want. It must be vacuumed clean and any loose material removed.

You need a mesh or EML that covers the entire plaster of each bay between the laths, and is rust resistant, or it will stain.

And is turned up at the sides so it can be rigidly fixed to the joists

I don't see how you'd turn band into mesh. Knitting?

 

[Gary111]

Haha thanks again so much mate

 

[cdbe]

You are allowed to patch a lath ceiling with plasterboard.

 

[Gary111]

Thanks, I have seen thistle multi finish plaster quite reasonable for 25kg, it says it's fine, do you think that will be suitable?

 

[Gary111]

Actually looking at the cracked ceiling from the flat below I'm wondering if it's too far gone to repair.

 

[Deleted member 174758]

If you have rotted laths they need to be removed, along with the plaster they are (just about) supporting. The source of the leak/water ingress needs to be identified and fixed. It is then better to just patch in some plasterboard onto the joists and then skim over that. Other than highly ornate, historically significant plasterwork (e.g. with ceiling roses or special cornices), badly damaged lath and plaster is generally not considered worth the effort of keeping in my experience (and replacing laths is a dirty, carp job)