Yellow stains on plaster wall patches

Question

I live in an old 1910s house and it turns out my walls aren't drywall. It is constructed of rock or some type of masonry. Over it, there is a really, really old wallpaper, which also have over itself, something covering it. It's 1½ feet wide paper-like sheet vertically pasted on walls and finaly, covered by many, many paint layers.

Yesterday, I went into a room in order to put some plaster patch on a damaged area. There was a spot, on the paper layers which I mentioned previously, which doesn't seems to stick anymore. So I simply tear it and it came off pretty easily, without too much effort (this is how I discovered the old, old wallpaper). So I applied some plaster patch on it to level it correctly. But once it has dried, some weird yellow stains appeared through the plaster patch. I'm guessing that at some point in the past, water damage or something may occurred at that location. However, when I touch it I don't feel any moisture.

• What should I do?
• Is this normal?
• Is it moisture or something like glue behind the paper-like sheets?
• Should I consider putting «placoplâte» in french (Plasterboard in english I guess or draywall) to cover all over these walls?
• Is there anything I must do to ensure my walls are really dry?
• Are these yellow spots appear on the paint too?

Thanks in advance. I must specify that it will be a new born child's room so I don't want to take any risks but I really want to do it on my own without paying for an expensive professional service.

Answer 1

Things can yellow for a variety of reasons, water, smoking, etc etc etc. It really depends on the materials you are working with as well. If the wallpaper came off that easily, water is a good guess.

• What should I do? Lots of options, I have two suggestions (see below)
• Is it normal? for a house that old, normal is a relative term, Ill go with yes
• Is it moist or something like glue behind paper-like sheets? There is likely glue of some sort, it could also be moist. You should ensure there is nothing (a leaking pipe perhaps) behind the wall. Its also entirely possible that there was water at some time in the past but it is no longer an issue.
• Should I consider putting «placoplâte» in french (Plasterboard in english I guess or draywall) to cover all over these walls? I wouldnt go over the walls, see my suggestions below
• Is there anything I must do to ensure my walls a really dry? Its definitely worth checking into. If you are already patching it wouldn't hurt to cut a small hole where you suspect moisture and verify there is nothing behind the plaster.
• Will it "sweat" over the paint I'll put over this or it stays only on my plaster patches? Not sure what you mean here. Will what sweat?

In my mind you have one of two options:

• The cheaper, easier option: Prep the walls to make them smooth and clean (in this case meaning free of dust and other things that can mess with paint). Repaint the entire room with an oil or alcohol based sealer/primer. Anything that is in the plaster (I am guessing this is plaster you are working with) this step will seal it in; odors, chemicals, stains...including the yellowing you mentioned. Once you have done that, paint the walls to your taste with a latex paint.

• The more expensive option: Get yourself a dust mask and a sledge hammer and some tarps for the floor and tear the plaster out (demolition is fun, but test for lead paint first). Replace with drywall. This option is obviously a lot more involved.

Good luck.

Answer 2

I personally think there is some sort of material in the Claster aggregate that causes oxidation with joint compound as I am myself dealing with this. For now we are just leaving the way it is and will just get a very quality paint to pretty much seal it. I am pretty much in the process of doing research on this phenomenan myself to figure out what is exactly that cause this oxidation—us I am very certain it’s from oxidation.