On Aug 13, 11:30 am, " wrote:
I can't say for certain, but recently I needed to set new glass into a
stone mullioned window. I made up a 3:1 mix of silver sand (labeled as
block paving sand at Wickes) and lime putty. Made it a lot easier to
get a good finish, has bonded well to the limestone masonry and so far
has proved stable.

On one occasion I also made up a mortar using building sand rather
than sharp sand (all I had to hand), and used it point in a wooden
window frame with quite satisfactory results. The usual sharp sand
lime mortar mix can be tricky with closely-jointed masonry, so I
wouldn't be afraid of trying alternatives for difficult locations.
Unlike portland cement, lime mortar can easily be knocked off if
there's a need to change it.

I've just mixed up a mortar that ended up about with 3.5 lime, 2 soft
sand, 6 sharp sand and 1 chalk. (It's a long story). The soft sand
and chalk has made if /very/ smooth and easy to push around ... and
the pointing hasn't fallen out since the weekend.

I wonder if the OPs fillet is made with a) hydraulic lime; b)
pozzallano's (sp?); c) Portland cement.