My bathroom walls, over the years, have had holes patched and wallpaper removed. The walls are blotchey and very unattractive. Is there an easy way to skim the walls and make them smooth?
Yes. The easy way is to hire a skilled plasterer. He can skim coat your walls to baby-butt smooth perfection and, in exchange, all you'll have to do is write him a check. Easy.
If you're willing to accept slightly less perfect results, you could probably do it yourself. But be forewarned, there's a learning curve, and the word "easy" won't enter into it.
Begin by cleaning the living daylights out of the walls. Remove any scraps of wallpaper that remain and scrub down the wall until they bleed. Then apply a very thin coat of setting compound such as Silver Set 90 with the widest trowel or taping knife that you can find – 12" is good. When that's set, knock down any high spots with the knife and then apply another thin coat of all purpose drywall compound. Finish up with a coat of topping compound.
Now if you have the wall-finishing gene, all you'll need is a few minutes with a damp sponge to wipe down any indiscretions and you'll be ready to paint. If you lack the wall-finishing gene, you'll need to spend some quality time with sandpaper.
Jolene, using traditional methods of spackle, sanding and paint to try and achieve a smooth surface on walls that have been so damaged over the years will be a lot of work, and even then, the walls will never be totally smooth.
Jim delivered some great advice below, but I wanted to point out one more option. That is to "skin" the walls with a new layer of drywall. You can purchase 1/4 inch drywall which is very inexpensive and quite thin. Attach the new drywall on top of the existing walls. Then just tape and spackle the joints, prime and paint. In the end, you'll have brand new walls!