We have removed wallpaper to reveal the original magnolia paint from when the house was built about 10 years ago. Some spots where I can see the plaster beneath it and obviously shiny bots of paste on the walls. Going to wash down with sugar soap, prime the walls and then look for any areas to fill/sand and then hopefully paint with our desired emulsion. Should this look ok? Or is it a lost cause?
I"d suggest misting the walls with a plant sprayer and lightly scraping it with a broad metal scraper. This will lift off paste snd fragments of papet as a wet slime When finished you can rub off with an old towel.
You won't need a primer. Apply emulsion paint to bare plaster or filler, two coats diluted with 30% water, followed by a couple of coats undiluted paint, preferably the same colour as the rest of the wall so the patches don't show through.
I've done exactly what you did OP and it was fine. The one thing I did do though was use a thick one coat Dulux paint and a stipple effect roller. I wasn't worried about trying to achieve a perfectly smooth flat finish as I had read up that the stipple would prevent light reflecting in a uniform way and which would highlight any blemishes. It's worked well and I don't notice this stippling.
I did this. I think the previous wall paper was put on with undiluted PVA, and then paint / some base coat was flaking off. I took this approach as I didn't trust a skim coat to stick to the flaking stuff. So it had to come off, and instead of taking back to brick I took it back to plaster as best I could. There were huge lumps of green sticky stuff that I scraped off with a wallpaper scraper, then a fair bit of sanding with rough emery paper to remove the last bits of paint, PVA and lumps in the plaster.
Next was a fair bit of filling due to previous holes and my scraping efforts. I used a very soft, cheap filler. Do not use polyfiller as it is harder than plaster so you can't really get a smooth finish! I found with the soft filler I could use my finger to 'sand' the top bit smooth before it had fully set.
After the initial fill and caulk to fill the gaps in the corners a couple of mist coats of watered down white emulsion (not B&Qs cheap one that doesn't water down well) give s a white wall. The next step is a perfectionists dream. At night get a spotlight and shine it along the wall. It highlights all the high points, and other bits that need filling. out with the cheap / soft filler again and fine sandpaper. The next night can paint a top coat.
Yes it took a long time. But it gave a good finish, was 'cheap' as I wasn't paying a plasterer. And I know the plaster is stuck to the wall.
I've had a bad experience elsewhere of a skim coat coming away from the wall, either because it didn't stick to the old plaster / paint / gunge, or because the old plaster itself started coming away from the wall ('blown' plaster).