I agree, but for "Get it as smooth as possible." I'd only knock down any bumps sticking out of the current thinset wall. Drywall mud will stick to it, and it will stick better to a rougher surface.

run a cord from another GFCI outlet and see if they trip that one too, If so it's the lights

Yup, same thing happened with me one year. One of the connections between a string of lights and an extension cord was wet.

Photo?

You didn’t post a pic.

What did the piece of plaster look like? That is very clean lathe to have just removed original plaster from it... and there are two remaining screws that would more likely be used for drywall or plaster boards.

See, originally I wasn't concerned because I was just going to replace everything with drywall anyway, but I don't have money for that, so now I just wanna fix it and make it not ugly lol.

I think that it would be easier to buy a 4x8 sheet of 3/8" drywall and cut it to roughly fit in the hole. Screw it in and mud on top (more labor, harder to mess up), or shim it out so that you just mud the joints (requires a bit of skill, but isn't too difficult).

Edit: Mudding the joints involves joint tape. If you want to match the texture, peel back a few inches of the existing texture so that you can tape from the old to the new...

+1 to this theory. This exact scenario happened to me last year. I replaced the GFCI and the outdoor outlet before realizing the problem was the lights themselves. Could be one of the strands are getting moisture in them, or some other issue related to the lights.

This is lathe and plaster.

Option 1 - Cut out a square area of plaster. Keep the strapping, and slap a 1/2" piece of drywall in there. Tape and mud the seems, then paint.

Option 2 - Trim the edges so they are clean, then re-apply plaster.

Option 3 - demolish the entire wall, and just hang new drywall off the existing studs. You may put in new bracing while you're at it.

I would also recommend doing epoxy floor, and treated wood at least for the bottom plate.

If you have an extension cord that will reach, try plugging string A into outlet B, and vice versa. See if problem follows lights or outlet. Are these LED lights? I installed an LED fixture in my garage and it would trip the GFI.. had to take it out. Never figured out issue.or some reason

Check to see if the wiring is correct. My garage plugs were constantly tripping. Had an electrician check it out and one outlet was wired backwards.

How does one end up ripping off a piece that large by "accident?" At this point, just keep going. Replace it all with drywall.

Have you done some radon testing lately? Might be a good idea so that you don't need to incorporate remediation later.

I had an unused bollard yard light that was corroded down the line from a GFCI. It was 20ft away but wired in.

Get yourself a bucket of joint compound and a wide trowel and pan. Put a thin layer of joint compound on it, trying to push some to key through the lath. Let it dry for like a day. Repeat the process until the plaster matches the existing plaster. Using a wet sponge, smooth everything out to match. Texture with a stomp brush to match what you got, prime, paint. It's a lot easier than you think.

I fixed a hole just like that doing this.

somewhat relevant:

https://youtu.be/iXaw70X7wb4

Well in that case you better go get some plaster repair at a box store. Next go out to your grandpa's/uncle's farm and start brushing out every horse and jackass you can find. As you collect the horse/ass hair be sure to keep it free of dirt.

When you get home tomorrow add approximately 2 cups of horse hair to every bag of plaster for the "authentic" 1906 traditional plaster. Smoooth out the best you can, followed by a minimum of 6 or seven layers of paint over the following week.

Should blend well

^^^ Definitely give this a go. For sure sounds like a problem with your lights .

Try plugging in something else that is known good, the lights may have developed an issue (could be a rusty wire arcing or other intermittent failure). If the other thing works fine, it's the lights. If the GFCI still trips, replace it.

I'm going to suggest that it may actually be the lights tripping it. Try a large load (like a space heater or a shop vac, ect.) and see if that trips it. You might have moisture where the lights connect into the other lights potentially causing issues also.

Best caulk for baseboards and door/window molding?

Old house with not perfectly straight walls and windows. Need to fill in a bit here and there. I’ve been told both acrylic latex or latex or a latex/silicone blend. All trim is painted white and I’ll touch up after caulking.

Looks like original rock lath. If that piece came off that easy, the rest of it is probably getting loose too. May want to find out why and fix it all instead of one piece.

You can either re-plaster it or fit a piece of drywall in there.

Unhook half your lights and see if it still trips