Lime plaster patch removed - fill with gypsum?

[lizziecupcakes]

Hi all,
We have some blown lime plaster in the corner of the bay area (bedroom). This was because the bitumen felt above in this corner had collapsed (not sure when) and rain, moisture had penetrated through gradually (through cracks in the lead flashing). Over a long period it time, it seems this is the likely cause of the blown plaster. It had become quite powdery to touch too.

We had this part of the roof repaired (with breathable felt) and new lead flashing - it’s water tight now. We did this about 2 months ago.

As for the like plaster that’s blown, We’ve hacked this area off now - back to brick- and the other parts of the lime plaster seem great and adhered to the wall fine. This wall is also the party wall.

I was originally going to let this area dry for a few good months and then lime plaster it myself. However, my plasterer is saying it’s bone dry and recommends we just apply gypsum plaster it and leave it (so I could potentially move onto decorating the room sooner).

In the future (maybe 5 years or so), I plan to actually go back to brick here. This is mainly because I want to add noise insulation against the party wall. It will be gypsum plastered too since it is not an external wall. I will only wood fibre board and lime plaster my external walls. Having said that, if the condition of the lime plaster seems fine, we may just leave it alone (we’ll see then).

My questions are:
- should I allow it to dry for longer? (it does look and feel dry to touch)
- should I use bonding gypsum plaster and then a skim of gypsum plaster just in this hacked iff area, or the alternative is that I apply lime plaster myself at some point?

My concern is that I want to be in this bedroom soon (it’s the main bedroom), but where it is hacked off, there is quite a bit of dust falling away from the edges of the plaster (which I believe is normal). I don’t want to inhale this nor have it ruin any furniture i may put in here.

Thank you

 

[Cubist]

Why is your plasterer suggesting gypsum? Why is he/she uncomfortable with making the repair with lime?

 

[mh12]

Hi LCC
Not an expert here but from my limited understanding plaster breathability is an important feature for externally facing walls.
As yours is a party/internal wall then gypsum should be fine.
You mention the possibility of DIYing the job in which case I'd be tempted to go with lime instead.
By the way I have zero plastering ability and experience at present.
Hopefully that should change in future.

 

[lizziecupcakes]

Why is your plasterer suggesting gypsum? Why is he/she uncomfortable with making the repair with lime?

Unfortunately, they don’t use lime - theyre not a lime plasterer. It’s the same plasterer i’m using for my ceiling - plasterboard and gypsum plaster is being used.

My query is more about whether gypsum plaster would be ok, and whether I should let it dry out for longer.

 

[lizziecupcakes]

Hi LCC
Not an expert here but from my limited understanding plaster breathability is an important feature for externally facing walls.
As yours is a party/internal wall then gypsum should be fine.
You mention the possibility of DIYing the job in which case I'd be tempted to go with lime instead.
By the way I have zero plastering ability and experience at present.
Hopefully that should change in future.

Thanks for sharing your thoughts. I’m so tempted to use gypsum now as it’s a small corner as I really just want to get into the bedroom. But i also want to do the right thing

 

[mh12]

Unfortunately, they don’t use lime - theyre not a lime plasterer. It’s the same plasterer i’m using for my ceiling - plasterboard and gypsum plaster is being used.

My query is more about whether gypsum plaster would be ok, and whether I should let it dry out for longer.

LCC...not sure if this will be of any help and although I have no direct plastering experience have been following various threads regarding lime plastering and have came across some interesting suggestion which your plasterer might find helpful...

Baumit Klima RK 38,​

behave a bit like gypsum base coat so theoretically your plasterer should be be able to work with this.

https://baumit.co.uk/products/healthy-living/lime-plasters-1/baumit-klima-rk-38 suggests you can base coat and finish coat with the same product.

 

[Lacan07]

Thanks for sharing your thoughts. I’m so tempted to use gypsum now as it’s a small corner as I really just want to get into the bedroom. But i also want to do the right thing

I think the question to ask is not so much about doing 'the right thing' but about how likely is that part of the wall to experience damp issues again. Its not a sizeable area and there's nothing wrong with patching it up with gypsum if the original issue is fixed. Gypsum doesn't do well with moisture, it tends to disintegrate rapidly. I plastered quite a few of my internal upper floor walls with gypsum. Once done you'll very quickly forget about it anyway.

 

[Cubist]

Thanks for sharing your thoughts. I’m so tempted to use gypsum now as it’s a small corner as I really just want to get into the bedroom. But i also want to do the right thing

I, like Lacan, would have no qualms about using a gypsum plaster for that repair. However, achieving a good final finish over that area with a decent blend line to the old plaster would be no mean feat for a first timer - maybe your plasterer would be willing to do this small repair or would he want to just get on and do the whole job?

 

[lizziecupcakes]

Thanks @Lacan07 and @Cubist , i think i’ll just go with the gypsum now then. it looks dried out.

This way I can move onto decorating in this room and actually feel like one room feels like a proper home .