Silica Desiccant

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Block Glass Windows
Desiccant for Replacement Windows
Silica Desiccant absorbs the moisture that exists between the panes of a multi pane window

Part of the process of maintaining windows involves replacing the desiccant compound to keep the window functioning properly.


[edit] Silica Desiccant

Silica Desiccant removes humidity from the insulated space that exists between the panes of a multi-pane window and enables the window to function properly. The silica desiccant is placed inside the spacer bar that exists within the window sash between the window edge and the air space. The spacer bar with its desiccant presents moisture condensation from developing between the window panes.

[edit] Multi-Pane Windows

Multi-pane windows act as insulating units to reduce heat loss through a window. These double pane windows or triple pane windows have a layer of argon gas, krypton gas or air which is trapped between two panes of glass to further insulate the windows. Since this air or gas, as is true with all gases, contains water vapors, the vapors can turn into droplets which condense on a window pane when the temperature on either side of a window reaches a specific level of heat or cold. Some windows also include a thin film which is installed between the panes that separate the space between the panes into two spaces. This further reduces heat gain and heat loss as the outside air hits the window. If multiple-pane windows exhibit a misty or foggy appearance it indicates that the seal protecting the window assembly has failed.

[edit] Silica Desiccant in Multi-Pane Windows

A desiccant is an absorbent material which is designed to protect a space by maintaining dryness in that space. In a multi-pane window, silica pellets are placed inside the aluminum perimeter strip -- the spacer bar. They absorb moisture that results from any incoming air that enters the space between the panes. Without the silica desiccant moisture in the space that exists between the panes would condense on the glazing unit as the glass cools below the temperature of the dew point.

Silica is able to absorb large amounts of water vapor due to its large surface area. When the sealant that protects the perimeter of the glazing unit fails, as it will over time, moisture-containing air will infiltrate the space between the panes causing the silica desiccant to become saturated with moisture. At this point condensation will begin to form along the perimeter of the glazing unit and the unit must then be repaired or replaced.

[edit] What this Means for Homeowners

Multi-pane windows will eventually fail due to the deterioration of the silica desiccant that breaks down, over time, within the windows' panes. The higher quality wood, wood clad, fiberglass and composite windows can last for 20 - 25 years with a good quality desiccant while the lower-cost aluminum and high quality vinyl windows with box spacers generally last for approximately 15 years if they have a good quality desiccant. During the daytime heat hits a double pane window which causes the air trapped inside the windows' panes to heat up. The sealed window unit expands as it pushes air out of the semi-permeable seals. In the evening the window contracts as it cools and draws air -- with the humidity -- with it. This cyclical expansion and contraction stresses the window seals and fills the air space with moisture and, over time, will cause the window to fail. South- and west-facing windows tend to fail earlier because the biggest cause of window failure is the windows' exposure to the sun which hardens the sealant that seals the window as the different air temperatures pass through the window -- "solar pumping." Silica desiccant is built into every thermal pane window frame to absorb the small amounts of moisture that are inevitably drawn into the window. Desiccant has a limited capacity and lifespan -- how limited depends on the quality of the desiccant itself as well as on the windows' framing material.

[edit] Window Repair

Repairing a window with desiccant failure is not simple but it can be done. The individual must remove one of the glazing panels from the frame and carefully clean both glazing panels. This is accomplished by removing all sealant from the glazing panel's perimeter and cutting through the edge sealant against the underside of the top pane of glass and through any adhesive that bonds the glass to the frame.

Sealant must also be removed by cutting around the aluminum spacer frame and lifting it away from the glass pane. All extraneous sealant can be scraped away from the perimeter of the glazing panel that remains sealed in the frame and both panes can then be thoroughly cleaned.

The spacer bar can be removed by gently pulling on the corner key after all sealant has been cut away. The spacer bar should remain horizontal to prevent the old desiccant from pouring out. Once the spacer bar has been separated from the frame, the desiccant can be poured out and the spacer bar is refilled with new desiccant. After the spacer bar has been refilled with new desiccant the sealed unit can be reassembled and refitted to the window frame.

[edit] Suggested Desiccant

Window experts strongly advise that only good quality glazing desiccant be used when repairing a failed window unit. These top performance desiccants, together with a professional repair job, assure a long life for the repaired sealed unit.

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