If it doesn't move when you press it I would try the first method. With the light coming across the wall like that you'll need to do a good job of feathering the filler, it doesn't matter if you go 10" across the crack as long as you don't see a bulge of filler over the scrim. You can use the lightweight toupret scrim to make life easier but it's more expensive per roll.
If it doesn't move when you press it I would try the first method. With the light coming across the wall like that you'll need to do a good job of feathering the filler, it doesn't matter if you go 10" across the crack as long as you don't see a bulge of filler over the scrim. You can use the lightweight toupret scrim to make life easier but it's more expensive per roll.