Merdalfthewizard
once more unto the breach
Depending on the size of the joint, If they're quite large (over 10mm) I go for a 3 sharp, 1 building and 1 cement mix, gives a smoother finish when pointing up. Smaller joints can be done with a bag of ready-mix bricklaying mortar (great for pointing, garbage for actually laying bricks) brushed directly into the joints and compacted down using a lump of wood as suggested above. I have filled joints with crushed glass fragments before, easy to do and adds a bit of colour, I think we got it from Jewsons but I could be wrong. Hope this helps