The hardened glass-fill method eliminates fading, oxidizing, maintenance cost, etc. Glass is inorganic, an inert substance and is not subject to chemicals, acid rain or infrared and ultraviolet rays i.e., sunlight. The hardened glass is impossible to fade, oxidize, or peel and is virtually maintenance free. For example, have you ever walked along the seashore and come across a piece of "sea glass"? It was once a part of a glass bottle; the glass is still brown or green. However, it has a frosted appearance from the abrasion caused by sand when the seashore tides move in and out. It is constantly in the ultraviolet rays, but it is still brown or green. Other fill methods, such as, paints, epoxies and grouts are organic substances and are subject to infrared and ultraviolet rays. Over a period of time, these substances will fade and break down due to sunlight, acid rain, chemicals and the environment. Cost and inconvenience becomes a factor in refilling each brick, or if left unattended, a cosmetically unappealing brick. In most cases, breakdown would result in replacement of the brick.
Epoxies (plastics) are susceptible to breakdown; they begin to shrink and fade. Shrinking allows moisture to build in between the epoxy and the brick. This may allow algae to grow, causing a maintenance problem and a cosmetically unappealing brick. Expansion and contraction is also a problem. The rate of expansion and contraction of epoxy vs. the brick itself are at different rates. This may allow the epoxy to separate from the brick. Paints and grouts are just as susceptible to breakdown, similar to epoxy. However, they are more susceptible to chipping, especially if pressure cleaning for maintenance is required. Just as you pressure clean a building to remove the old oxidized paint to prepare for repainting; this same effect would occur with the bricks, causing a maintenance problem and a cosmetically unappealing brick.