JK wrote:

Do you mean that all in one thick insulating board with foil on the back.
Scary, never done anything like that!

If you're scared by insulation board, damp proof injections must
terrify you!

Seriously, it's much easier to dry line. While I'm here, I'll
second BigWallop's advice - injecting won't achieve anything.
Don't bother.

--
Grunff