water stain on plaster on wall

[Explorer-8]

About 3 years ago, I had water stains appearing on one of my living room walls, one of the kitchen walls and on one of the landing walls. I later discovered that it was the lead that was loose on the flat roof of my kitchen extension. I had new lead put on and the stains didn't get any worse after that.

This year, I stripped the wallpaper in the living room. Even in spite of the stains on one wall, every wall was in poor condition and so I had them skimmed by a plasterer. This week, I sized them and emulsioned them.

Now, tonight, I have seen a water stain appearing in exactly the same place as the original one, but not as big or as prominent. I have had a look out of the window and the lead looks firmly fixed onto the flat roof of the kitchen.

My question is, how, after several years of drying out, and a new layer of plaster plus emulsion, can that stain be coming back?

[RATTER15]

What you need to do now is to call in a damp proofing specialist who will check the wall for damp with a meter (this should be free) and if it is in fact damp will tell you where the damp is coming from. it is possible that the stain you are looking at is a bit of damp being held by hygroscopic salts left from the previous problem, if that is the case it will dry out again.

[Explorer-8]

Thank you, Ratter. I will do that.

[skylight]

I had a leak in my roof and it came through my bedroom ceiling. After it dried out I painted the stain with white undercoat ,twice ,to seal it. Then I gave the ceiling two coats of emulsion. It has never reappeared. Skylight