On Saturday, 22 September 2018 22:42:11 UTC+1, JimK wrote:

Mmm but how do you get at them once they're found?
Are you thinking you/he'll be able to reuse the top deck?
Might be cheaper for him to just rip it up & renew than tit about
attempting to find & remove screws buried in roof
compound?
How thick is the roof coating anyhow?

The membrane should be around 1-2mm thick and so I was intending on just gouging/scraping it away from the screw heads once located.

The top deck will be scrap as I don't imagine it'd be cost effective to try and remove the membrane from the entire surface to enable reuse.