repairing paperless face of plasterboard?

[redhexagonal]

So the stringer of my stairs was buried in a wonky plasterboard wall, and I want to put quadrant molding on top of it. I decided to sand back the dot and dabbed wall through the skim and paper face of the plasterboard by 5mm total, then put expanding foam into the gaps by the stringer and through a couple of small holes I drilled in the face, and then I painted the face of the exposed board with Gardz, applied mesh tape all over it, then skimmed with easifill . The area is 7 inches high in the corner and goes to zero over 3ft of the stringer. I know the correct way is to replace the board, but there is a waterproof membrane behind the board and I'm not sure if there are adequate fixing points to put dab onto unless I replaced a large area. Is my method going to work ok?

 

[Wayners]

Yeah probably.
I've done similar.
The surface mesh gives back strength.
Trouble happens if board starts to crumble when taking off surface but looks like you avoided that

 

[redhexagonal]

Yeah probably.
I've done similar.
The surface mesh gives back strength.
Trouble happens if board starts to crumble when taking off surface but looks like you avoided that

I sanded it back pretty cleanly with an orbital sander. it feels solid, I guess the test comes when I bash it or kick it accidentally. I'm wondering if I should put another layer of Gardz or BIN over the easifill before painting?

 

[Wayners]

One gardz is fine. Another will start to run.

 

[RandomGrinch]

As I read it, the original gardz was to seal the sanded plasterboard.
Yes, I would paint some gardz over the easifill