Jo pretended :
We have an old Levensulme air raid shelter in our garden which is used as a
shed - brick built with a concrete roof. The roof has started to leak. What
would be the best way to fix and waterproof this?

Get the concrete scrubbed clean, then cover with hot poured bitumen,
with a top covering of bitumen felt similar to what is used on wooden
sheds, but heavier grade.

A more expensive option would be to add a pitched roof over the top of
the concrete.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk