Large patch for lime plaster over brick

[mrbiscuit]

Hi All,
Quick one - I've got the inside of an exterior wall with a large patch (about 1m square) that needs patching. The bare brick is sound, but the edges of the lime plaster are a bit crumbly.
I really don't want the job to turn into anything too big.
As such I've brushed it clean and liberally coated it with dilute pva several times.

My question is this - what's the best thing to patch it with? The lime plaster is about 2 - 2.5cm thick.

I was tempted to use bonding, but the wall is about 500m from the Cumbrian coast and gets battered by the weather, and I was worried about moisture absorption by the bonding from the bricks.

Would cutting a piece of plasterboard and fixing it in place ready for some multifinish be a terrible idea?

Thanks in advance.

 

[RandomGrinch]

I am no expert!
But, I believe the absolutely best thing to do would be to patch with lime plaster I'm afraid!
Standard plaster over the top of lime (or next to it in this case) could lead to damp retention and blown plaster in the future
Letting a damp exterior wall 'breathe' with lime plaster is a good way to keep the wall dry.
Alternatively, If I had to, I would go for your plasterboard patch, rather than the solid bonding and skim.

 

[jacko555]

I am also not an expert!

But...

I do have a 100yr old house with original lime plaster and cavity walls that's had various repairs over the years.

Do you have cavity walls or is it a solid wall?

The bathroom has 2 external walls and was gypsum skimmed by previous owner 5 years ago - no damp or blown. Also North facing.

I've used bonding to fill some very deep holes (woodwormed picture rails were nailed with with floorboard brads which made big holes when removing)

I've also used plasterboard to cover the wooden lintels over windows (needed to check they were not rotten so exposed when by chipping of the plaster/removing the lathes), and skimmed over the top of that.

I think the key is the cavity walls. Any moisture is dealt with by the cavity being ventilated.

If there wasn't cavity walls I'd have used lime.

Maybe helpful?

 

[RandomGrinch]

Yeah good point Jacko, my walls are rubble filled stone walls (so theoretically a cavity, but tightly filled with all sorts!). Wherever the previous occupier has skimmed, the plaster has blown! Wherever there was damp, the previous owner had rendered in cement!
Removing the modern stuff has given me a dry house back, although yes, I have over boarded in places!

 

[mrbiscuit]

Thanks for the suggestions.
I eventually cut a piece of plasterboard as tight a fit as I could make and skimmed with multi finish. So many other jobs in the house have turned into major episodes and I wanted a quick win, LOL.
I do know that lime plaster would have been for the best, and if this proves problematic I will re do the job 'properly'