On Friday, 15 May 2020 17:53:20 UTC+1, Broadback wrote:
I need to extend a path sideways. I have place edging along side which
in places have left gaps. What is the best product to fill in with? I
think that standard mortar will be too weak, whereas concreted would not
go into the narrow gaps. Suggestions please.

How wide is the area you are trying to fill. Use finer aggregate in the concrete ie 10mm instead of 20mm

Richard