Rendering question

[Mabozza]

Looking to help someone out by doing some rendering for them as they are getting water ingress and damp walls.

There are several areas that need doing but there is one area I'm not sure about. As per pic, the the previous guide tracks / rails have rusted away.
I assume new guides need installed, but how would I remove the remains of the rusty old ones?

[reggie747]

Angle grinder on standby and a hammer and scutch chisel will see that off.

[KAgantua]

How will rendering fix the damp?

[Mabozza]

This is letting in water

KAgantua said:

How will rendering fix the damp?

[Mabozza]

reggie747 said:

Angle grinder on standby and a hammer and scutch chisel will see that off.

thank you!