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From Birth to Death (and then Restored) --The life-cycle of glass units:
Insulating glass units are not really hermetically sealed. They are constructed from two pieces of glass held apart by a spacer bar with either one or two mastic sealer beads applied around the edges. The space between the glass is pretty much sealed up -- but not entirely so. With changes in air pressure inside compared to outside the glass unit small amounts of air leak in and out. This leakage usually increases as the unit ages. The air which leaks into the unit (as well as the air enclosed during manufacturing)  contains moisture in the form of water vapour. This moisture is anticipated during manufacturing of the unit by the inclusion of a dessicant (usually silica pellets) which are contained inside the spacer bar. You can notice small breather holes on the inside edge of the spacer bar which allow the moisture in the air inside the glass unit to be absorbed into the dessicant inside the spacer bar.
This system works well until the dessicant pellets reach the end of their useful life and become saturated with moisture. After this the moisture in the unit begins to condense onto the inside glass surfaces of the almost sealed glass unit. At first this appears as a light misting and then progresses to heavier condensation which may come and go as temperature and humidity change. Gradually the condensation problem inside the glass unit becomes worse.
 As the water inside the unit cycles through the evaporation and condensation cycles, water spots and mineral deposits begin to accumulate on the glass and become heavier over time. As the sun shines through these mineral deposits on the glass it causes small amounts of silica to leach out of the glass surface. We describe this condition as ‘mineral etching’. Similar to sandblasting, it results in a dulling of the glass surface and is a permanent, non-repairable condition.
Defogger’s Thermal-Glass Restorations can remove moisture from failed glass units. We also wash the inside of the unit using several cleaners to remove water spots and mineral deposits. We cannot repair mineral etching.
If you have failed insulating glass units, contact us to have them restored sooner rather than later. If you leave them in a failed condition for too long we can get the moisture out, we can clean dirt and deposits from the inside glass surfaces, but once they get mineral etched, we will not be able to restore them to like-new condition (though often the improvement is still dramatic and impressive).
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