What You Actually Find Under Old Trim
Most people expect nail holes. That's the easy part. The real problems are usually one or more of these:
Paint shadow lines. If the trim was there for any significant length of time, the paint underneath is a different color from what's on the rest of the wall. Sometimes it's the original wall color from before a repaint. Sometimes it's years of UV exposure that faded the surrounding paint while the trim area stayed protected. Either way, patching the holes and painting over the whole thing doesn't work.
My neighbor Herb, who spent about 20 years doing commercial finish work before he retired, calls these tattoos. He says old paint lines are sometimes impossible to completely hide without painting the whole wall. He's not wrong, but you can get close enough that nobody notices without standing right against it.
Adhesive residue. Any trim installed after the 1980s may have been glued in addition to nailed. Panel adhesive is brutal to deal with. It either tears off the drywall paper when you pull the trim, or it stays on the wall in dried globs that are impossible to paint smooth.
Torn paper facing. The paper face of drywall holds everything together. When you peel trim off aggressively, or when adhesive pulls it away, you're left with exposed gypsum core. That gypsum soaks up paint differently from the rest of the wall. Every patch you apply over raw gypsum will look different no matter how much you sand it unless you treat it first.
Dealing with the Paint Line Problem
This one you can't sand away. Trust me, I tried. I spent about two hours with 120-grit paper on that dining room wall trying to feather the edge of the old paint line and it just made things worse. I'd removed the top layer of paint and still had a visible depression where the trim had been sitting against the wall.
The right approach is to skim coat the entire area rather than just the damage spots. That means spreading a thin coat of all-purpose joint compound across the whole section where the trim ran. You're creating a uniform surface rather than trying to fix individual spots within a paint transition zone.
Use a wide knife, at least 10 or 12 inches. Mix your compound to a smooth consistency, slightly thinner than you'd use for regular patching. Apply one thin coat that covers from a few inches above the old trim line to a few inches below it, blending the edges out as far as you need to. Let it dry completely, sand lightly, and do a second coat if you see any ridges. Two coats of compound plus primer will usually bury the paint line enough that it disappears after painting.
When You Need to Prime Before Skimming
If the old trim line is really stark, or if you've got torn paper underneath, hit the wall with a coat of PVA primer before applying any compound. PVA primer seals exposed gypsum and gives you a consistent surface to work on. Skimming directly over raw gypsum without priming first will cause the compound to dry unevenly, which shows up when you paint.
Dana walked by while I was doing this step and asked why I was painting the wall before plastering it. I said something sarcastic. She still mentions it at gatherings.
Removing Adhesive and Fixing Torn Paper
For construction adhesive left on the wall, your options depend on how hard it has cured. Fresh-ish adhesive can sometimes be scraped off with a flexible putty knife without damaging the drywall underneath. Old, fully cured adhesive is a different story.
If it's stuck solid and you start scraping aggressively, you'll tear the paper. At that point you're better off leaving the adhesive in place and skimming over it. Sand the edges of each dried glob lightly to reduce the profile, then skim coat over everything. The compound fills in around the adhesive and sands flat. You lose a little on thin spots but it's workable.
For torn paper, the fix is straightforward but requires patience. Apply a thin coat of compound directly over the torn area with a 6-inch knife, feathering it out about 4 inches on each side. Let it dry. Sand the edges lightly. Apply a second coat slightly wider than the first. The goal is a smooth surface that blends into the surrounding wall. Most torn areas need three coats to look right, which means three separate drying cycles.
Herb suggested using setting-type compound for the first coat over torn paper because it doesn't shrink as much as regular compound when it dries. He's right. I've switched to hot mud for the first coat on any torn paper repair and the results are more consistent. Just work fast because 20-minute mud means you have about 15 minutes before it starts setting up.
Nail Holes Along the Trim Line
These are the least of your problems. Fill them with spackle or lightweight compound, sand flat, and move on. The only catch is placement. Trim nails typically run in a line across the wall at a consistent height. If you fill each nail hole individually and don't skim the area, you end up with a row of small bumps or depressions that become visible under raking light after you paint.
So if you have more than four or five nail holes in a row, don't spot-fill them. Skim the whole section as described above. The nail holes will disappear as part of the skim, and you avoid the row-of-dots problem entirely.
Spot-fill only when you have two or three holes spread randomly. In that case, use lightweight spackle, let it dry, and sand with 120-grit wrapped around a sanding block. Never bare fingers. Your fingers follow surface variations and create low spots you won't notice until you paint.
Priming Before Painting
Don't skip primer. I know everyone says this and most people ignore it. But skim-coated compound and freshly exposed gypsum absorb paint at completely different rates from your existing painted wall. If you roll paint directly over repaired areas without priming, the patched spots look flat and chalky compared to the rest of the wall. This is called flashing, and you can see it especially clearly in indirect light or from an angle.
Use a drywall-specific primer or a PVA primer on anything you've skim coated or patched. One coat is usually enough before your topcoat. The Gypsum Association recommends priming all repaired drywall surfaces before finish painting, and in my experience skipping this step means an extra coat of finish paint at minimum, and sometimes two extra coats before the flashing disappears.
My total cost for the dining room chair rail removal and repair was about $28 in materials: joint compound, PVA primer, and sandpaper. About six hours spread over three days for drying time. The room looks completely normal now. Dana has not mentioned the chair rail at a single gathering since.