In article ,
"John Schmitt" writes:
In hot weather it is a good idea to damp mortar and concrete down every so
often. If the mixture dries out, the hydraulic cure will not take place
properly.

Thanks John, I did do this.
After the neighbours saw me walking down the valley gully sprinkling
what probably looked like grass seed (but was actually dry sand to
remake the mortar bonding strips on the GRP gully), and then saw me
watering it all afternoon, they probably think I've either given it
some pagen ritual blessing, or they're now waiting for the roof garden
to spring into life ;-)

BTW thanks for your comments and your FAQ which I browsed before
starting. One area in which it seems very difficult to get much hard
advice is the sand/cement ratio, type of sand, and other additives
for any given application. I think I had ratios between 1:2 and 1:4
suggested. My roofer tells me they used to use 1:3 for this, but
nowadays it's done with 1:4 using a 50/50 mix of building sand and
sharp sand. It would be good to see a chart somewhere ranging from
the strongest through to the weakest mixes, and typical usages of
each.

--
Andrew Gabriel