I have done so much research but can't find an answer to this question. We moved into a house a few years ago with a loft conversion. The walls were pale cream colour and we didn't notice anything odd until we painted them red. Then the internal wall with the velux window (so, adjacent to the roof) started exhibiting this weird chalky substance. There was no damp smell and it washed off easily with light soap and water; however, it will return after several weeks.
I did some research and though it had something to do with the paint quality, so I bought a sealant, painted that on the wall, then added two coats of a blue coloured paint.
It seemed okay for a couple of months, and now it is more visible than ever.
I had added two pics. One is how it looks before trying to clean it off (fine white veins), the other show a square patch I cleaned and how it looked 1 month later.
Any ideas what this is, and how I can get rid of it?
This looks like mould is formulating in behind the plasterwork and seeping through. You need to get your hands on a professional mould remover that can penetrate plaster. Typically a really good hardware store will have this or a local damp proofing company that sell damp proof products. When you have that done you need to keep the room well ventilated and the heat on for some time so the room drys out. When it all drys out you need to keep ventilating the room every day or couple of days. Would also be worth looking at your roof to make sure none of your window flashings is leaking or tiles broken.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!