I have a front elevation of a red brick Edwardian terrace which needs reporting in a tuck-point - a red backstop mortar with black putty ribbon inlay.
Could you offer some advice on the knocking up of the lime putty and aggregate/dyes to use for the black ribbon? I have tried a test panel with the 1 part putty to 1-2 parts fine silica silver sand (Wrotham-Kent) with average results. I am having difficulty achieving the correct constancy of the putty - i.e. it should be malleable like glazing putty, however generally its either too sloppy (1 part sand) leaving smug marks on the red back-stop mortar when trimming with the Frenchman, or too stiff (2 part sand) making the ribbon crumble when applied with the iron. Does the putty need to be stiffened in an ambient environment prior mixing the sand?
Also, any advice on the black dye I should use. Currently I am using black oxide (up to 10% in weight of the lime) and still not achieving pure black - more a dark grey
Note: I'm using the 4 month matured Cornish putty, which is probably now been approx. 6+month in storage.
Thanks in advance.