Dark spots on wall after replastering

[SCET2459]

Hi,

I've had the wall in my hallway taken back to the brick and replastered with lime plaster as the existing plaster was a bodge of lime plaster and gypsum and there were historical damp issues.
This wall is a party wall as the house is a Victorian terrace.
After painting it what I'm finding now though is that right on the line where the new lime plaster meets the existing plaster there is rising dark spots.

Does anyone have any idea why that would be?

I've had other areas of the house replastered with lime plaster without any issues.

Thanks
Scott

 

[aockenden]

What is the plaster above? Is this a wall with a chimney? Is there a ventilated suspended floor system or solid floor? Definitely need some more info.

 

[SCET2459]

I believe the plaster above is lime plaster and the floor is suspended. If I'm wrong about the plaster above could that be the cause? I would have thought with my limited knowledge that if it was gypsum then the 'damp patches' would appear above or around the gypsum rather than through it.
On the other side of the wall is the hallway of the other house. Their bathroom is directly above the hallway.

 

[noj]

A couple of questions.
1. How long ago was the new lime plaster applied and had any previous damp fully dried?
2. Can you have a friendly chat with your neighbour and see if they've had any issues or leaks on their side?

Dark, breathable paint will show any moisture in a more dramatic way than almost anything else...

 

[SCET2459]

The new lime plaster was applied about 11 months ago and there wasn't any issue in that immediate area before that I can remember, the issue was more just to the right of it where it was all gypsum rendered. I asked the neighbour if they had any issues but they only moved in a couple of years ago and they haven't seen anything from their side.
I know what you mean by dark breathable paint, if I painted it a much lighter colour I may not notice as much but I'm curious as to why the spread of the darker colour is exactly where the new plaster joins the old plaster.

 

[malcolm]

If everything you've put on there is breathable it should dry out in an annoying amount of time. The lower part of a wall where I replaced cement with lime took 2 years to dry out and for the damp spots to go away because the wall was so wet.

The damp spots on the plaster outside where you re-plastered might be because the old plaster has been skimmed with gypsum and can't dry so fast as the new plaster. Should dry eventually as the new plaster dries the wall. I would play the waiting game and see what it's like next year.

 

[chrisfraser05]

I'm not expert by any means, joined this forum looking to right some of the wrongs I made renovating my last (1907) property when i buy the new one (1830/50s).

If the above and below the line are both lime, the main difference would be age, and potentially salts built up in the older plaster if there has been historic damp.
Salts being hygroscopic I'd imagine they are pulling the moisture from the wall or air better than the newer plaster.

Have you been checking the room for humidity levels?

 

[Kearn]

Old saturated bricks take an age to dry out. What you’re likely seeing is internal moisture finding its way out… could go on months, possibly a year or two.

If it comes and goes periodically, I’d be more concerned.

If it doesn’t ever go, then again…!

The join in the plaster is probably also an easier exit point…

 

[SCET2459]

Thank you all for your replies. It's put my mind at rest as such, I'll monitor it for another year and see if the dark patch gets any bigger or if it decreases.

 

[Lacan07]

How soon after the lime plastering was the wall painted? I'm guessing you allowed sufficient time for the lime to migrate to the surface.

 

[SCET2459]

I left it for 7 months before I started painting.

 

[Lacan07]

I left it for 7 months before I started painting.

Good stuff.

I'd just monitor it for now, as has been mentioned above if the wall was damp previously it may take a while to dry out.