Much of my house is pointed with a lime and sand mix that I did over 20 years ago following the advice of my neighbours. It is as good as the day it was done. There is no way that I would ever consider adding cement to pointing. The Grand Designs wall must have had a problem either with the mix or the weather. If you want to quote Grand Designs I suggest that you listen carefully to what Kevin McCloud has to say on the subject.
Due to the different expansion rates and amounts with cement and limestone they will always pull apart. Only handy thing with cement is the stone comes off clean allowing it to be re used easier than the lime which will bind to the lime forming a proper bond.
A lot of 150 year old buildings have fallen down, there is no strength in these old houses just 1m thickness, ours are 1/2 m. and lots of cracks due to no foundations.
If they had used even 10% cement the house would have been sound.
Very few old buildings around me had any lime pointing, my own buildings used only mud. As I keep repeating lime and sand are perfect, cement will introduce more problems than it cures.
Lots of cracks due to no foundations will not be improved using too harder mix of either lime or cement. Cement being harder will not help. NHL 3.5 or 2 allows for structural movement which you will not stop. There is a reason why brick/block walls require expansion joints when cement is used and not when lime is used.
In your house you can do what you want. Telling us we are all wrong and don’t know what we are talking about is just rude.
We cut 12 windows to make our building into a house, there was a lot of mud left over so we mixed it with cement for the returns and then rendered that with Enduit to give a smooth surface and painted that with white gloss.
Done 11 years ago still perfect, perhaps not so white cos French paint does not stay white.
We base our workings on what my wife`s father taught us, not wrong.
Probably working differently is not wrong either, just different.