AbsoluteBeginner

I haven't mixed mortar for over twenty years.... and this is my first post! A builder suggested to me that the sand cement mix I should use for a particular task is equal parts sand and cement. Its quite complicated to explain exactly what its for though its to be used in small amounts on top of gaps to fill. Its obvious to me this is quite different from what is advised on countless websites so why might I have been advised 1:1? What would the properties of this mix be? Any clues gratefully received!

Previously I've only part-renovated a house before, kitchen/bathroom/re-wire/repaint/new carpets (ok, just planned and then paid the bills). The current work is on a cottage from 1860 with damp issues, and the renovation has been forced on us by a severe flood. The insurers aren't paying for build-back-better as it happened last year and they had only joined the scheme for policies starting later than our renewal. Regardless, we've so far not found builders or surveyors with good knowledge of how to apply flood resilience on an old property when the normal wisdom is to let everything breathe. We have a builder now, seems a good sort and so far admits when he doesn't know something.