When installing glass block windows, Mortar has always been credited as the traditional method. That was before the invention of silicone, which now can be used for the same purpose. There are certain advantages of both silicone and mortar.
Advantages of Mortar
With mortar joints, you are given the opportunity to use various sizes of joint between bricks to allow for odd shapes. Existing masonry can be blended to match the new block installation with little obvious changes. It is also extremely tough and durable, so breaking a glass block window is not easy when there is a mortar joint in place. Mortar can be quite messy to deal with and takes time to apply. It can also set too quickly in heated conditions.
Advantages of Silicone Mortar
Silicone would be a more preferred method for bathrooms, or when an all glass appearance is preferred. The joints are smaller, more slim, and less obvious. Silicone is white and reflective, and when placed between the joints of glass bricks, it will more or less disappear. Spacing is smaller, which means more light can come through from the glass blocks. Silicone is also less messy to apply. It can be put on using a caulking gun, whereas mortar has to be buttered on and situated before it sets.
Hints and help