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Repairing a lath & plaster ceiling.

 
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Hairyloon



Joined: 20 Nov 2008
Posts: 14556
Location: Today I are mostly being in Yorkshire.
PostPosted: Sat Sep 10, 16 12:51 pm    Post subject: Repairing a lath & plaster ceiling.  Reply with quote    

A friend has had a velux window fitted in the bathroom and the job did not include making good on the plasterwork which is an old lath & plaster construction (well, not old on the scale of these things.
I have read that it is best to repair with a lime mortar similar to what was originally used, but I have never worked with that so I know nothing much about it.
Any top tips? Or is it just easiest to use modern plasters?

Either way, what needs to be done in respect damp proofing, with regard to it being in a bathroom?

dpack



Joined: 02 Jul 2005
Posts: 32592
Location: yes
PostPosted: Sun Sep 11, 16 10:18 am    Post subject: Reply with quote    

modern plaster is easier and more damp resistant ,avoid bonding coat/browning as the stuff is a sponge.

non hydrolic lime plaster ready mixed is around 10 for 25 kg and would do the job but

this stuff is super sticky and sets very hard which is ideal for patching around a velux at around 25 a bag

other patching plasters are available but if you go for one of them ask the builders merchants if they are suitable for A around a window frame and B in a bathroom and C will it stick to lath .

re sticking , wire brush the lath then prime with waterproof pva diluted 3 to 1 allowed to almost dry will help.

Hairyloon



Joined: 20 Nov 2008
Posts: 14556
Location: Today I are mostly being in Yorkshire.
PostPosted: Sun Sep 11, 16 11:47 am    Post subject: Reply with quote    

dpack wrote:
modern plaster is easier and more damp resistant ,avoid bonding coat/browning as the stuff is a sponge...

So use an undercoat plaster that isn't bonding or browning?

Quote:
non hydrolic lime plaster ready mixed is around 10 for 25 kg and would do the job but

Sorry, but you're being ambiguous: lime plaster is the traditional stuff, so is that your recommendation if I want to take the traditional route?

dpack



Joined: 02 Jul 2005
Posts: 32592
Location: yes
PostPosted: Sun Sep 11, 16 1:22 pm    Post subject: Reply with quote    

traditional = non hydraulic lime , 2 coats let the deep one set slowly keeping it damp then do a thin smooth top coat to level out any shrinkage and cracks, let it set slowly keeping it slightly damp .

non traditional but lime based = use the super plaster stuff one coat troweled level, let it set slightly damp.

another option is a bathroom rated one coat patching plaster, fill and trowel, let it set

browning and bonding are cheap (ie good for big deep areas) and usually end up nasty , the only thing they are good for are internal upstairs walls and even then i avoid them.

EDIT i would go for onecoat patching plaster unless a lime plaster was specified for a listed building which seems unlikely as they have a new velux

Last edited by dpack on Sun Sep 11, 16 1:56 pm; edited 1 time in total

Ty Gwyn



Joined: 22 Sep 2010
Posts: 3947
Location: Lampeter
PostPosted: Sun Sep 11, 16 1:48 pm    Post subject: Reply with quote    

I presume with the opening cut for the velux there is a minimum of making good to be done on the lath work?

Hairyloon



Joined: 20 Nov 2008
Posts: 14556
Location: Today I are mostly being in Yorkshire.
PostPosted: Sun Sep 11, 16 3:27 pm    Post subject: Reply with quote    

dpack wrote:
traditional = non hydraulic lime , 2 coats let the deep one set slowly keeping it damp then do a thin smooth top coat to level out any shrinkage and cracks, let it set slowly keeping it slightly damp .

non traditional but lime based = use the super plaster stuff one coat troweled level, let it set slightly damp.

another option is a bathroom rated one coat patching plaster, fill and trowel, let it set

Not at all bothered about being traditional, but it has to go on pretty thick, so I'm not planning to do it in one coat.

Ty Gwyn wrote:
I presume with the opening cut for the velux there is a minimum of making good to be done on the lath work?

Pretty minimal, yes.

Ty Gwyn



Joined: 22 Sep 2010
Posts: 3947
Location: Lampeter
PostPosted: Sun Sep 11, 16 4:04 pm    Post subject: Reply with quote    

Thistle mixed with sand for the first coat,well pressed into the lath`s,then finish with a thistle coat,just as good if your not fussed on a traditional finish.

Hairyloon



Joined: 20 Nov 2008
Posts: 14556
Location: Today I are mostly being in Yorkshire.
PostPosted: Mon Sep 12, 16 7:31 am    Post subject: Reply with quote    

Ty Gwyn wrote:
Thistle mixed with sand for the first coat,well pressed into the lath`s,then finish with a thistle coat,just as good if your not fussed on a traditional finish.

Damn. I've strimmed all the thistles. I'll have to wait for them to grow back...


On a more serious note, how much sand?
Thanks both for the tips.

dpack



Joined: 02 Jul 2005
Posts: 32592
Location: yes
PostPosted: Mon Sep 12, 16 2:05 pm    Post subject: Reply with quote    


Ty Gwyn



Joined: 22 Sep 2010
Posts: 3947
Location: Lampeter
PostPosted: Mon Sep 12, 16 7:18 pm    Post subject: Reply with quote    

Hairyloon wrote:
Ty Gwyn wrote:
Thistle mixed with sand for the first coat,well pressed into the lath`s,then finish with a thistle coat,just as good if your not fussed on a traditional finish.

Damn. I've strimmed all the thistles. I'll have to wait for them to grow back...


On a more serious note, how much sand?
Thanks both for the tips.


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