How do I prepare the walls for wallpapering?

[DIYalot]

Hi. My home was built in 1958. In the 1970's the walls of the lobby were painted. I've removed all paints from the walls. There were 3 coats, the last coat would have been put on about mid 1970's. The final coat was glossy and bubbled up when paint remover was applied. The very first coat did not bubble up, but was softened by the paint remover and I scoured the wall with a scourer and warm water and washing-up liquid.

So, the walls are essentially free of paint, there is just a faint colour remaining.

I've actually got two types of wall situation here, #1 and #2.

Wall #1. The surface of the plaster (white) is really quite smooth.

Wall #2: Here, the skim plaster surface was actually removed and will need to re-plastered.

Okay, regarding wall #1: Do I sand down this wall? I think I do. Also, do I need to paint the wall with a primer, perhaps I do, since the plaster is not new? Again, I think the answer is yes. Although I don't know what to buy.

Regarding wall #2: The substrate that the new plaster will adhere to is of two types. Part of the wall, the substrate, is really soft, it's easy to rub it down with the fingers. Another part is very hard, I'd say that is called browning. Not sure if the other soft substrate is called browning, it's a very light colour.

Now, after the wall is skimmed with plaster, will that wall also need to be sanded? And, will it have to be primed? I suppose so, even though the plaster will be new, with I suppose, the same primer used on wall #1.

Your guidance appreciated. Thanks.

EDIT: Aaah, I think, unless anyone says differently, I need to use something like Zinsser GARDZ for wall preparation.

 

[Chri5]

If it's a standard lobby why not do away with any fluffing around and get all the walls skimmed?

Since some need doing, the it really won't add too much to the cost (I'm still seeing a lobby, smaller area).

Skim walls tend to be stabilised pre skim, normally with a pva water mix- that varies depending on what the plasterer feels is appropriate.

Post skin and dry, mist coat 50:50 paint and water (this is like a primer coat, it get sucked in by the plaster and gives grip to the full coats).

 

[DIYalot]

Well, it's quite a large lobby, I mean, it's about as big as a small kitchen, it's sort of a hallway-ish that we used to pass through before getting into the part of the house where we lived. Before I realized a heat gun would work on the walls, I'd already removed the plaster from one wall.

I think what you are saying is that to avoid water being taken out of the plaster skim, the substrate would be stabilised/sealed. And in that case, once the skim plaster is on the wall, you would not need to apply a sealant/stabiliser on top of the skim. Is that correct? But, on the other wall, I need to put a sealant on top of the old skimmed plaster. Rich.

EDIT: Oh, I'd still put some form of sealant after skin and when it's dried. Just seen that.