If he's used white spirit, then he's probably contaminated the pads (Gonna have to replace them! ) In future use Muc off disc brake cleaner , really worth the money and it doesn't really matter if it gets on the pad (Although try to avoid it anyway!) Make sure the piston is pumping out well, not sticking! New calipers and worn ones can stick so you will need to remove it, pump out the piston and clean it with a cotton bud and blood oil, then carefully push it back in (You may ned to Re-bleed) this should lube it up nicely! Nearly forgot, The disc should be fine once properly cleaned!