Double pane windows provide added insulation for your home or office by placing a gas layer between two panes of glass to impede the transfer of heat through the glass. This means you lose less heat in the winter and gain less heat from outside in summer. The gas, usually argon, is sealed between the two layers of glass in the manufacturing process. If the seal is compromised, however, condensation can form between the panes and mould can grow there.
Contact a professional glazier. The only process recognised by the National Association of Certified Home Inspectors (NACHI) must be done by a professional glazier. The process is controversial and there is considerable debate among NACHI members as to its efficacy or long term cost-effectiveness.
Drill a hole in an inconspicuous corner of the glass. This process requires professional equipment not available to the homeowner and must be done by a professional window glazier. A small hole is drilled in a corner to provide access to the space between the panes.
Spray a cleaning solution between the window pains. Once the window is breached, the glazier attaches a sprayer and sprays a cleaning solution mist through the hole into the pains. The solution will include an anti-fungal chemical that kills and loosens the mould.
Vacuum out the solution and moisture trapped between the panes. The glazier attaches a vacuum device to the hole and sucks out the cleaning solution, debris and as much moisture as possible.
Attach the defogger device. The glazier then permanently inserts a defogger device into the hole in the window that allows the release of moisture during thermal pumping. The device will remain attached to the window permanently to prevent condensation.
The appearance of mould or condensation between double pane windows means the seal on the glass has failed. The glass should be replaced if at all possible.
The so-called "defogging" process is a stopgap method for dealing with a window that has failed. Once the seal in a double pane window has failed, NACHI recommends that you replace the glass if possible. Because of the way some windows are made, you may find you have to replace the entire window frame and all. Defogging does improve the cosmetic appearance of the window and may reduce the potential damage that can be caused by moisture and resulting mould and rot. In a situation where window replacement may be difficult or impossible for physical or financial reasons, defogging does provide one option for addressing the problem of mould inside double windows.