In your friend's case, the plaster walls likely never received a finish plaster coat. This was a fairly common practice, the idea being that the walls would always be papered.

The the brown fuzzy paper is probably what's left of glue and wall paper. If the plaster beneath is smooth and hard, just continue what you're doing. If it's sandy and crumbly, you have the same type of wall as your friend.

A finish plaster coat can be added to old walls or joint compound can be used. (The joint compound does not give a hard, durable finish like plaster but can be used by an amateur.) Plastering is a highly skilled trade, so this option is expensive. Adding a layer of joint compound is a long and not so easy process. New wallpaper may turn out to be the best option.

Plaster is made from gypsum, lime, and water. If the lime used in the original mix was agricultural grade, the plaster will be brown or some variation of brown when it sets up, due to the impurities in the lime. There is nothing wrong with brown plaster, it will protect the wooden structure of the building from fire damage, just as white plaster would. Your friend with the crumbling walls can learn to do plaster repair if she is willing to make the effort. She will be able to get decent results with some effort, but the results will not be totally smooth until she has maybe 100 hours of experience at this. It is much easier for a beginner to apply plaster to a wall, as opposed to a ceiling.

"A finish plaster coat can be added to old walls or joint compound can be used. (The joint compound does not give a hard, durable finish like plaster but can be used by an amateur.)"

Depending on the area of the country you may be able to find someone skilled one coat plaster who can do the job.

Setting joint compound like Durabond is as hard as plaster.

The biggest trick is not using drywall knives, but an actual plasterer's trowel to cover large areas.

The "biggest trick" is about 20 years of practice! The pros are true craftsmen. It is hard enough for a novice to do a decent patch job, let alone coat a whole wall/room.

I got the hang of finishing off plaster after a room or two. It's an art, and it's like icing a big cake. LOL. Well worth learning if you live in an old house with plaster walls. You can still find wet plaster craftsmen here, but they're a dying breed.

I used this stuff on problem walls. You can paint it any color you want. I got a lot of complements on it, and a friend is using it under the chair rail in her foyer.

Here is a link that might be useful: Paintable wallpaper

"The "biggest trick" is about 20 years of practice!"

Everyone starts somewhere.

No one was born with 20 years of experience.

Covering large areas with drywall style knives is not worth the trouble.

It takes some practice and decent tools, but is not really that hard.

Many of the plasterer's trowels at the big box stores have round handles so small you cannot raise the leading edge easily.

When I was renoing one house, I had a crew scraping wallpaper etc. Even with lots of elbow grease, there was such little progress that it was cheaper to knock off the plaster, pull the lathing (nasty unmilled strips) and drywall. In other cases, I have drywalled over crumbly plaster walls and even ceilings. So call me a sinner.

When I married into this house (LOL) every room was wall papered. I have been methodically removing the paper from each room. Finishing off the plaster correctly and painting them. Paper steamers are not expensive. There still may be scraping involved, but I've gone out to eat a decent meal and paid more for it than I did my paper steamer. Rent one and try it if you want to see how much easier the job becomes. I've redone so many walls in so many houses, regardless of how lovely paintable paper or new wallpaper is...........it's the kiss of death because it always makes me wonder what is really under it, and why isn't it painted? Ditto highly textured walls. Seen it done by so many people who didn't want to rip it back and put a lot of work into it. The ironic thing is, we re-did a room a couple years ago to a perfectly smooth wall and we had a contractor helping on this one. He wanted to put a textured stucco finish on it. ACK! The first thought was somebody will think we are hiding something, and we just spent major money to get it perfect! But, I was outvoted, and it's beautiful........but to a home renovator, it's a conditioned reflex, I suspect.

"Everyone starts somewhere." Yes, but apprentices start next to a craftsman.

We had no experience with plaster and did quite well when using the Magic Trowel. It was the best $15 we ever spent. Yes, we still had to sand, but it was minimal and some of the walls were very bad.
Diane

One of my most exciting vacations was to an Italian villa which was a 17th century farmhouse in Umbria. I took 2000 plus pictures of the house and the gardens.

I mention it because the walls were plaster but the converted barn had stone walls. That plaster throughout the house was in excellent shape, and the colors were warm and earthy, and they did not appear to have any repairs to them. I think they know how to live with old structures in Europe, in general.

So when I came home to our house with textured plaster walls, I decided to take a more laid back approach to what the house was--a 1950 cottage in south Alabama built like a fortress but with a LOT of things out of square and no good reason to fight with it.

BUT, with the DH's Cape style house in MA, built in post WWII MA in 1948, we had reams of wallpaper on those walls. One day when he was busy downstairs, I went upstairs and quietly began removing wallpaper in the two newer bedrooms. He almost had a heart attack. Never having lived in a house with plaster walls, I did not realize the problems I could uncover if the walls were not good beneath. So he came behind me removing glue and tidying up any bad spots (not many since he built that addition 30 years ago.) However, when I removed paper from the original parts of the old bedroom downstairs, it did require plaster repair on walls and ceiling.

I've seen folks make repairs using the dry wall compound over the old plaster. That was the way our Alabama bathroom had been repaired before. And, it was a total disaster. When I began demo of the one bath, I discovered rot and mildew in the walls, crumbling stuff behind the toilet, rotten wood ready to put someone through the floor while sitting on that john. Without hesitation, I tore out the bathroom while I had hubby out of town, and got the contractor over to install a new 3/4 bath until we could replace the original bath with all new fixtures and a solid floor. We miss the tub for now, but will be really pleased when we wind up with a new (drywalled) master bath.

"I've seen folks make repairs using the dry wall compound over the old plaster."

The premixed drywall mud in buckets makes a huge mess.

The setting type drywall compounds (powder you mix with water) work very well. They are a plaster type produce that hardens by chemical reaction, unlike the pre-mix that 'hardens' by drying out.

Whatever you use to patch plaster be sure to dampen the edges of repairs.
The old plaster will pull the water out of any patching material very quickly.

If the patching material is plaster or setting joint compound it will not harden correctly if it dries out very quickly.