Paint your walls with 2 coats of paint (in most cases): You should be ready to paint at that point. Sand with rough (100), then transition to, finer sandpaper (120) and then prime with drywall primer pictured above (only one coat is needed in most cases).Large repairs will need tape and you can find how to do that in this post on preparing walls for paint.Deep patches will shrink: no way around that. Patch the hole with a pre-mixed drywall compound and give it a day or so to dry, and add a second or even 3rd coat if the dried patch keeps shrinking.You have to assume those cracks will keep moving over years. It’s faster, and it stretches a little whereas other spackle and mud compounds will not. One trick is to fill tiny cracks with paintable caulk.For mold, it’s the primer you see here, (comes in quart or gallon), but please read my post about mold-resistant paint. You’ll have to prime that with a stain-blocking primer such as Kilz Premium or a good product called 1-2-3. If you see a brown discoloration, that is probably a water stain from years of moisture and maybe leaks in the roof, etc. Use a putty knife to remove any loose plaster.This will cause some cracking which you just patch up with spackle (sand all when dry). If the plaster wall is still firm and has just separated from the backing “lath” which was usually cedar strips, you just need to re-attach with drywall screws. Plaster walls are usually cracked but are worth saving. The best paints don’t fade, go on easier, and last longer than a well-advertised big box store brand. What paint? Pick whatever you like, but here is my best advice: don’t skimp. Comes in a one-gallon, or buy 5 gallons (shown) for the price of 4 singles. Painting plaster walls that are in good shape: prime any bare plaster (or drywall), with basic drywall primer. Read about stain-blocking primer (scroll down to #3). Just spot prime with shellac-based primer (nasty, nasty). Some stains will still bleed through after some years, so you need to go nuclear. Water-stained walls? You need a stain-blocking primer. (For old plaster, I don’t recommend any paint-and-primer-in-one). Right here at the top, you will be happy to see my top primers and paint. Often plaster walls have a lot of lime so mold cannot grow in them. Plaster walls are harder to prep and paint than modern drywall, but it is great to save them, and it will probably cost you less in the end. Plaster Walls are worth saving and painting Painting Plaster Walls is not at all difficult.