Discolouration through skimmed ceiling

[jayc89]

I've recently had our dining room kitchen reskimmed. It was in pretty poor condition, it had lining paper which I stripped off to find old cracked, but not loose, plaster. The cracks were covered using scrim tape and the entire ceiling was then "blue-gritted" before being skimmed using multi-finish.

 

It's been a couple of months since it was skimmed so it should be well dried out now (I painted other rooms in the house that have been reskimmed after a couple of weeks!). There were a few darker patches in the plaster, but I didn't think anything of it and applied a couple of coats of white wash (50/50 contractors emulsion and water). Those darker patches were still visible after the white wash as brown/orange spots, after 4 coats of emulsion now, they're still coming through, although fainter.

 

I'm not sure what they are, but I'm guessing I need to put something on them to neutralise them before painting again?

Any help would be greatly appreciated.

[markc]

Sounds like they could be rust spots but to reoccurs there must be assitional moisture, any chance of a small leak above?

[jayc89]

There are radiator and hot water pipes running through the void above, but they're all brand new pipes (copper for the rads and hep for the hot water) and the patches seem to be scattered all over the ceiling (4m x 4m), not in any sort of pattern I'd have associated with water ingress (but I'm no expert...). Some small patches (size of a 2 pound coin) some larger, maybe 20cm, some round, some longer strips etc.

 

I really hope not as we've just redecorated upstairs...

[jayc89]

Not the best lighting to show you, but hopefully you get the idea

 

[markc]

Hmmm, really not sure, maybe @nod can help

[tonyshouse]

Old gloss paint , two coats then when fully repaint two coats with the original roller 

[jayc89]

1 hour ago, tonyshouse said:

Old gloss paint , two coats then when fully repaint two coats with the original roller 

 

I'm probably being simple here, but I'm not sure I follow - are you suggesting the marks are from old gloss paint? (Even through the bluegrit and skim?)

 

What's the best course of action given it's already had 4 coats of emulsion? Whilst the marks are getting lighter with every coat, at this rate I think it would need another 4 coats!

[saveasteading]

To paint over rust stains and plumbing leaks, I have used stain blocker paint and it works very well

Quite expensive for a small tin, but one coat does it.

It is then good at accepting emulsion in a single coat.

 

I have had a different problem with paint colours, where several areas gave become lighter. I am pretty sure this was because I used Painter's Mate to fill some cracks and hollows, and it seems to absorb the colour.  Moral...use powder filler as intended.

[tonyshouse]

I use oil based paint to seal staining, nicotine and tar go through both oil and water based paints but chellac stops them (knotting compound) 

[jayc89]

7 minutes ago, tonyshouse said:

I use oil based paint to seal staining, nicotine and tar go through both oil and water based paints but chellac stops them (knotting compound) 

 

Makes sense. I have some of this - https://www.toolstation.com/colron-knotting-solution/p62212?store=MG&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=s_dc&pcrid=515847200306&pkw=&pmt=&gclid=Cj0KCQjw5JSLBhCxARIsAHgO2SexHqu4BcVNROpnXXqgTzmNzlmpLus1SZtaBkByKGpjFLkG5NoZrLkaAi2QEALw_wcB&gclsrc=aw.ds - is it worth trying some on one of the smaller patches first? The solution itself is quite dark so I'm guessing it will need a couple of coats of paint too.

[James Newport]

zinsser BIN is shellac based as well, but it's white already.