They are constructed from two pieces of glass held apart by a spacer bar with
two semi-permeable seals which also serve as adhesive strips to secure the glass panes to the spacer bar.
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 through the semi-permeable seals.
Understanding The Problem:
A thermal glass unit is like a small greenhouse. The air between the two panes can heat up
dramatically when the sun shines on the glass. This causes changes of pressure between the
panes which affects the humidity of the air inside.
When thermal glass units are new, water absorbing pellets in the spacer bar absorb moisture. Over
time, the pellets become waterlogged and no longer function. This allows the moisture trapped
between the glass to evaporate and condense repeatedly. This eventually leads to scaling of the
interior glass surfaces.
The air which leaks into the unit through the semi-permeable seals (as well as the air enclosed
during manufacturing) contains moisture in the form of water vapour. The moisture in the unit then 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.
Leaving it too long can cause Mineral Etching...
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.
Don’t Be Disappointed...why you should act now.
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, though often the improvement is still impressive it will not be restored to new looking.
Our restoration process, which includes the installation of a micro-vent
directly on the surface of the glass solves the humidity problem between
What you end up with is a window which defogs itself and stays
permanently fog free. Once our technicians have done their work, the fluid
dynamics within the glass unit are different.
The micro-vents become active when heat or sunlight increases pressure
within the window causing the water vapour to escape through the micro-