Re-done the kitchen in magnolia, however there is a patch in one corner drying darker than the rest, tried a primer then magnolia and it still came through, also tried the BIN Zinnser stain/damp block stuff and it's a bit better but still coming through :-( Any advice? One wall meets next door (stone) and the other bit of the corner is behind the stone pillar for the back door, was going to weatherseal outside but I have nothing to seal unless it's coming through from next door or somehow seeping through a painted stone pillar? It doesn't feel wet to touch.
You have a water stain from an unknown source, Zinsser BIN is the wrong product to use for this application. You say 'It doesn't feel damp' use a damp meter to get an accurate result. The area will need to dry completely before any type of remedial paint is used, you will find when dry Zinsser 'Cover Stain' to be a more suited product, apply 2 coats. You need to treat the cause and then make good to the decorating.
Agree, trying to work out what could be the cause.... so as well as covering some untreated damp I was using the wrong product to try and cover it. I'll try and get some pictures later.
There is no cavity, the houses were built circa 1883 so it's plaster over stone between the 2 houses, what is odd is that I have only noticed since painting magnolia, it was filthy as the tenants wrecked the place, so gave it a clean the re-painted next day, hadn't noticed damp there before :-(
It's above the living room, another tale of woe :-( was an untanked wetroom but sorted that! Put a full suite in and had to replace the floor joists, ceiling and re-build the partition wall it was above.