Sanded acrylic latex caulk can fill cracks and feather into existing stucco better than smooth caulk
There are about ten paragraphs on why stucco walls crack, and Kirk Giordano (Kirk Giordano's Plastering) isn't going into it right now.
In this case, the stucco, about one-inch thick, runs down to the concrete slab, which is about three inches thick.
When it rains, the expansive soil lifts the house, as it drys, the house settles back down. When it settles, hairline cracking around window openings appear.
You can repair those cracks with caulk; Kirk uses Mor-flexx sanded caulk to blend in with the stucco. As Kirk explains why caulking the stucco cracks isn't always the best idea, because "...something's gotta give, it's either three solid inches (of concrete) or one-inch (of stucco)," he discovers scope creep in real-time on video.
Kirk discovers a hollow sound, so he doe3s what anyone would do: he starts whacking it with his hammer.
He uncovers the wall profile: a layer of stucco over the stucco,
"You know what guys, that's not a great idea, but at least we've located the weak spot right here.
Wow, okay, I've opened a can of worms, but that's okay. Nothing we can't handle."
He peels off the loose stucco with his trowel and then highjacks a load of mud from his daughter as she moves it to the addition they're plastering.
Plastering is about improvising.
After cleaning the opening with a wire brush and wetting the surface with a bonding agent, he fills the can of worms, getting back to the original point of the video: crack repair with caulk.
To make the caulked seam disappear, use a sanded caulk. Different brands have different sand, so you may be able to dial in a better match based on the stucco in your area. For this house, he thinks Mor-flexx is about right.
If you ask him about caulk for sanded grout, he'll say this:
"Ha. You coul;d use those caulkings, but the grout has finer sand. So, when you're trying to match this, you can see, it's much heavier sand."
For small cracks, you can apply caulk over them and then work it in and feather it out with your hands and a trowel. Polyurethane caulk will not work for this.
To feather in the stucco that's patching the can of worms, he uses a wet sponge float to ease the edges into the existing.