Lath and plaster - sticking it back?

[monkey writer]

Hello! I am new to this lark. We have recently bought a victorian property and on the stairs the lath and plaster is loose from the cieling. Now I read somewhere that it is possible to stick it back again, to avoid ripping it all off and re-plastering (with plasterboard probably...) If anyone knows how to do this I'd be most grateful.

Monkey

 

[NT]

The L&P _is_ the ceiling, I assume you mean loose from the joists.

Use props to push the L&P back up into place, with sheet ply on top of each prop to spread the load. Props can be fancy wind up jobs or just wood sticks the right length. Fancy props are easier to work with. Obviously lift it all together to avoid breaking the ceiling up.

Once L&P is in place, go into the loft and pour diluted pva along the sides of the joists, this will glue the lime to the joists. Give it all 2 or 3 of days to dry and remove props.


NT

 

[monkey writer]

ah ha! very cunning, thanks. Unfortunately this is a staircase which goes under another staircase - the ceiling is at an angle running on the underneath of the stairs - so maybe I could take up some of the stair tops and pour the glue in like that. I'll look into it. Or do you think replacement with plasterboard would be more sensible?

Thanks!

 

[Nemesis]

Replacement with plasterboard would be a very bad thing to do, conservation wise. Far better to try to repair. and practically it's a very, very messy job to remove old plaster.

The basic philosophy when working on historic buildings is to repair not destroy, and repair using like for like mateials.


You can also use stainless screws with large washers to try to screw some loose plaster back to the joists.

If you have to remove some plaster from the laths and replaster, then keep the laths and use lime.

http://www.thisoldhouse.com/toh/tvprograms/houseproject/article/0,16516,197893-195050,00.html

 

[NT]

If you use stainless screws and washers, and drill shallow recesses where theyre fitted, so theyre not proud, I expect that would be the easiest way. I've not done it this way, I imagine you'd need a fair few fixing points to keep point loads down.

Bringing an old L&P ceiling down is something to be avoided at almost any cost. It will trash anything and everything in the room. So I'd forget the PB option.


NT

 

[BMcD]

If you wish to hold it in place whilst you make the repair, then instead of acrow props or sticks whicn get in the way, why not find where the joists are and screw into them a sheet of plasterboard or ply wood over the loose area to support it. If you can then get to the ceiling above to check out the state of the lath and they seem well fixed to the joists still (most water damage to L & P ceilings or walls is due to the laths warping when they dry out and this in turn breaks the plaster nibs off which holds the ceiling up) then hoover out all debris and dust, dampen down and pour a haired sand:lime (3:1) mix between the joists. This will bond to the existing plaster and envelope the laths within. When it has gone off, remove the board from the underside and heypresto one ceiling restuck to the original laths. All you need do is fill the cracks and screw holes and coat with a decoration of your choice.

NB If the lath has come loose from the joist or is broken then (from above) screw some sheets of rib lath (a type of EML) into the joists and wire the lath to this for extra support (it might be worth doing this anyway)

If you want a plasterer try this link http://www.plaistererslivery.co.uk

 

[NT]

Is using lime in some way better than pva? More original I'm sure, but I'm aware than pva will stick wood laths to wood joists and lime to lath.


NT

 

[BMcD]

Lath and plaster ceilings can be quite weighty and perhaps to much for PVA to cope with, where as a haired lime mix wiill have the body to take the weight and also the tensile strenght with the hair included. If you want a faster set then the inclusion of casting plaster into the mix will acheive this.
Of course it wouldn't hurt and may well be better to incorporate both methods

 

[bournonite]

Have you figured out whether the plaster has detached from the lath, or the lath from the rafters?

If the plaster has detached, and the lath is ok, you might as well take the plaster off and re-plaster. Very hard to ever re-attach it - as BMcD says - its very heavy and if the nibs arent there to hold it - forget it.

If the lath has detached - Jim says use a lime/hair mix and pour over from above if possible - otherwise use closely spaced stainless steel screws along the line of the rafters to re-attach the lath. Only problem with this is if the lath has come adrift because it is rotten. Often its just because the pins holding it to the rafter have rusted away, in which case the steel screws will work. Drive them through the plaster and then fill over the top with a lime topcoat.

And don't use plasterboard, otherwise no-one on the forum would talk to you again!!!!!!!!!

 

[BMcD]

bournonite wrote:

If the lath has detached - Jim says use a lime/hair mix and pour over from above if possible -

Surely this will just add weight to an already unstable ceiling with no firm attachments to the joists.

Perhaps if you read my post carefully then you will see that I mention the state of the lath.

bournonite wrote:

otherwise use closely spaced stainless steel screws along the line of the rafters to re-attach the lath.

Presumably from the under side. The problem with this is you don't know if the screw goes through the lath or not also you could split the lath and added to that you have weakened the ceiling by perforating it like a postage stamp.
Much better to re attach the lath from above as I suggest then pour on the mix which will envelope the whole lot. Read my post for full details

 

[Gervase]

I would strongly recommend gauging your repair mix with a good scoop of plaster of Paris to give extra strength and a quick hold. It's not 'inauthentic' as repairs were carried out in the 18th century using similar stuff.
Put the repair plaster on a lot wetter than you would a normal plaster, and brush it well into the top surface with a wallpaper brush or similar. If you want to make sure of a good repair (if, say, your woodwork flexes a lot) paint on a layer of plaster slurry, cut some hessian or jute scrim to fit between the joists on top of the wet mix and then paint some more slurry over the top of that.
I'm inclined to agree with BMcD on putting yet more holes in lath. In my experience, once lathing has failed, it's pretty brittle stuff - particularly if the failure is due to saturation/drying twists or rusting of the nails. A few judicious repair washers (galvanised or zinc passivated, as least the size of a tu'penny piece) screwed in every few feet would be as far as I'd risk.

 

[BMcD]

Further to Gervase's advice about gauging the mix, Plaster of Paris and Casting Plaster are the same thing. I thought I ought to mention this to avoid confussion

bournonite wrote:

If the plaster has detached, and the lath is ok, you might as well take the plaster off and re-plaster. Very hard to ever re-attach it - as BMcD says - its very heavy and if the nibs arent there to hold it - forget it.

The method I posted is considered an highly effective way of conserving Lath and Plaster ceilings. Especially those with decorative features which would also need replacing should you take down and replaster
What I propose is effectively renewing the nibs by sandwiching the laths between the existing plaster and the new plaster poured from above