Assessing What I Was Actually Dealing With
The first thing I did was look at the back side of the damage. The hole was big enough that I could shine a flashlight inside and see the studs. The nearest stud was about 4 inches to the left of the hole. That meant whatever patch I cut would have to be supported from inside because I could not catch a stud.
The scrape running down from the hole was shallow. The paper was torn in two places and the gypsum core was exposed for maybe an inch in each spot. The rest was just a deep scuff in the paint and paper surface.
I decided to handle these as two separate repairs. The hole would be a California patch (the technique where you cut a piece of drywall larger than the hole, then snap off the gypsum to leave a paper flange). The scrape would just be paper-taped and skim-coated.
Materials I Already Had
Here is what I used. Almost all of it was already in my basement shop from previous projects.
A scrap of 1/2 inch drywall, about 12 inches square. Joint compound, the premixed all-purpose kind in the green-lid bucket. Mesh tape for the small spots and paper tape for the scrape. A 6 inch and a 10 inch taping knife. A utility knife with a fresh blade. 220 grit sanding sponge and 120 grit for the rough work. A scrap piece of wood about 16 inches long to use as a backer.
The only thing I had to buy was a small can of matching paint, which my wife had not bought enough of when she repainted the hallway two years ago. That was the $18 in materials, basically. The drywall, mud, and tape were all leftovers.
The Hole Repair
First step was squaring up the hole. The hit had left a jagged edge with chunks of broken gypsum hanging on by torn paper. I cut a clean rectangle around the damage with a utility knife, taking it out to clean drywall on all four sides. The rectangle ended up about 5 by 6 inches.
For the backer I used a scrap piece of 1x3 pine. Slid it through the hole vertically so it covered behind the entire opening, then ran a drywall screw through the existing drywall into the wood on each side. Now I had something solid behind the hole.
Cut a piece of drywall to fit the rectangle. Snug fit, not forced. Screwed it into the wood backer with two drywall screws.
First Coat of Mud
Mesh tape over all four seams of the patch. Then a first coat of joint compound applied with the 6 inch knife, pressed firmly to embed the tape and feathered out about 2 inches past the tape on all sides.
I left this overnight. Premixed mud takes longer than the can suggests, especially when you apply it thicker than the recommended amount, which I always do on the first coat over a deep patch.
The Coat I Had to Redo
This is where I messed up. The next morning the first coat felt dry to the touch so I went ahead with the second coat. Wider knife, smoother surface, feathered out maybe 6 inches past the patch.
About two hours later I noticed a slight bulge in the middle of the patch. The first coat had been dry on the surface but still wet underneath, and the moisture from the second coat had soaked back in and lifted things. I had to scrape it all off, let it actually dry for another full day, and start the second coat over.
The lesson is one I have learned about four different times. When the mud feels dry, it is not necessarily dry. On thick patches, wait a full 24 hours minimum before the next coat. The USG joint compound technical specs note that drying time depends on temperature and humidity. In a Midwest hallway in November I should have known better.
Fixing the Long Scrape
While I was waiting for the second coat over to dry, I worked on the long scrape. This was easier than the hole.
The torn paper edges had to come off. I lightly sanded the entire length of the scrape with 120 grit until the loose paper was gone and the surface was smooth. Wiped it clean with a slightly damp cloth and let it dry for ten minutes.
For the two spots where the gypsum was exposed, I cut short pieces of paper tape and embedded them in a thin layer of mud. The rest of the scrape just got a skim coat of mud, feathered wide on both sides with the 10 inch knife.
This dried much faster than the hole patch because the mud layer was thin. By the next morning it was ready for sanding.
Final Sanding and Painting
I sanded everything with 220 grit. Light pressure, checking for high spots with my hand. The patch was slightly proud in one corner so I knocked that down. The scrape area sanded out flat first try.
Primed the bare spots with a quick spray primer because my wife had the only can of regular primer at her place getting something else done. Spray primer works fine for small patches and dries in 10 minutes.
Painted with the wall color. Two coats. The patch is invisible. The scrape area, if you know where it was, has a very slight texture difference that I can feel but not see. Devon walked through the hallway last weekend and did not notice. That was good enough for me.
What I Would Do Differently
Two things. First, I would have waited longer between coats from the start. The do-over cost me an entire day of drying time and probably $2 worth of mud. Not a huge loss but also entirely preventable.
Second, I would have used setting compound (the powder kind that mixes with water) for the first coat over the hole instead of premixed. Setting compound dries by chemical reaction in a set time. It would have given me a hard, predictable first layer to build on, and I could have moved to the second coat the same day. I keep meaning to start using it more for patch work and I keep forgetting because the premixed stuff is right there in the bucket.