Pointing of granite in the Post Office wall, Penzance.

Anyone told you that it is rude to point?

Pointing is done to ensure that water is carried down the wall surface, to prevent it penetrating horizontally or into the perpends and into the horizontals. A good mason knows what mix to use for each type of stone and stonework. Stone should be able to move with the temperature, whilst the pointing forces water down to the next course. To seal the wall entirely on the external surface will allow trapped water to continue down the internal structure of the wall. When it hits the lower level of a potential rising damp situation, a moisture bridge is formed. That is encouraged to rise, despite gravity, by internal capillary attraction. In that way water can rise to up to six feet from ground level. So good pointing prevents penetration but also allows the masonry to breath and drain. Each method is individual to the mason and masonry. It is not done to achieve decorative effect as an art form. A good builder knows how to set window and door frames at such a depth in the masonry to allow water to drip down without horizonal penetration of the fabric. Pointing is a skilled science. A good mason also should be aware that some stone is 'porous', that is it has metamorphic content and internal veins. I will never forget the idiot bureaucrat that asked me to define what granite was, and define its strength. He considered the material inferior to concrete block. He also later wanted the pointing to be continuous. Which would have been disastrous. Relying on rule books and with no experience on site or with the vernacular. I despair.

Now I know why I am no builder nor architect, Treeve! Thanks a lot for elucidating!