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Lifting the Fog

Originally Published in MotorHome Magazine

Repairing fogged dual-pane windows restores vision while improving aesthetics

Temperature control inside a motorhome is of prime importance to occupants, and the use of dual-pane windows is a proven method for regulating heat in summer and cold in winter. Opting for dual-pane windows — when not offered as standard equipment — is one of the best moves potential owners can make when choosing the right motorhome.

No one will argue that dual-pane windows are much more efficient than their single-glass counterparts, but the benefits sometimes are overshadowed by fogging, which renders the glass unusable, especially in the cockpit where vision cannot be impeded. Fogging is a product of moisture penetration between the panes, which discolors the glass to the point where it becomes opaque and restricts vision. Beyond the aforementioned visual safety factor, fogged windows are just plain ugly and detract from the look of any motorhome.

Once the windows are fogged, the owner has two choices: repair the existing glass or buy a new window and frame. The latter is very expensive, and at times finding the right window can be a real challenge, as model-year changes dictate available inventory in the aftermarket. Southern California-based Reliable Glass, in conjunction with Redlands Truck & RV in Redlands, California, offers a service to repair fogged windows and, after 15 years rebuilding dual-pane windows, has perfected the process and boasts a 99% success rate.

While building dual-pane windows these days is not exactly rocket science, sealant quality plays a big role in whether a moisture breach will occur, and generally how long the window will remain clear. Reliable Glass uses a proprietary sealant and will not disclose the properties but guarantees that it will prevent moisture penetration and facilitate the most effective repairs possible. The company will not use butyl tape, which can creep onto the glass over time, and warns against the use of silicone-based products for sealing the windows.

Whether a window will leak and subsequently fog is dependent on the original structure and the quality of the aforementioned bonding process. Leaks typically originate at the edges of the windows where the moisture penetrates the air gap. If allowed to leak for a long period of time, the moisture can etch or stain the glass and require replacement. If the glass can be retained, it will be thoroughly cleaned and reinstalled. In some cases, the silicone-based sealant lets loose and the window panes can actually be pulled apart by hand. In this situation, penetration of moisture is greater, and the panes suffer from visual loss more quickly — and may not be cleanable.

If new glass is required for windows in the cockpit, it should be tempered. Reliable shies away from using plate glass, which is not as safe in a vehicle environment. When plate glass breaks, large shards of glass can act as projectiles and cause injury. Tempered glass breaks into tiny pieces, just like the side windows in any automobile. Some companies will offer plate glass replacements as an alternative, and even replace a dual-pane configuration with a single plate of glass, which loses the thermal benefits of dual-pane windows.

Repair Tip

Don’t wait to make repairs once the windows show signs of fogging. The fogging will likely not get better, and once etched, repair is more expensive.

Another option in the marketplace is the use of laminated glass, similar to the structure of a windshield. Providers will laminate two pieces of glass to make one contiguous unit that’s mounted in the frame. Laminated glass is heavier and may restrict movement in the frame sliders, making it harder to open and close the window. And, again, the occupants lose the benefits of an air gap, which will impact heating and cooling.

Fogging windows is fairly prevalent in the RV industry, especially in older motorhomes, and for this project, the driver’s side, living room windows in a test coach had lost much of their visual acuity. While removing (and reinstalling) the windows is not complicated, there will be a hole in the wall during the repair process, so self-sticking plastic sheeting is used to seal the opening temporarily. It takes two people to pull out the window once the screws in the frame are removed.

After separating the windowpanes, the technician will attempt to clean the glass. If there’s no etching, the glass will be cleaned thoroughly and the process to make the repairs continued without having to cut and temper new glass. From here, the Reliable technician will lay down a dense foam spacer before positioning the next piece of glass on top of it.
This procedure adjusts the thickness needed for the window frame. Finished thickness varies among suppliers, and the test window was 7⁄16-inch, which required two 1⁄8-inch glass panes and a 3⁄16-inch spacer. In lieu of the dense spacer, the use of butyl tape is still being practiced at repair shops because that’s the way first-generation dual-pane RV windows were manufactured (late 1990s and early 2000s). Reliable suggests that any repair using butyl tape be avoided for reasons stated above.


Redlands Truck and RV

Reliable Glass

A desiccant is used to absorb the moisture that becomes trapped in the air space when the glass is sealed to the spacer. This is an important aspect, since moisture levels vary depending on the time of year, weather conditions and location. A final application of sealant closes the windowpanes permanently. Prices for renewing the window are dependent on size; the cost for repairing one side-window was $450, including the labor to remove and reinstall the window.

Just about any dual-pane window can be repaired, even frameless versions. While frameless windows are aesthetically pleasing, the people at Reliable are seeing a fairly high rate of failures, mainly due to the mechanism for opening the windows. This can be attributed to pressure on the inside pane as the crank is tightened to close the movable section of the window. Over tightening can pull apart the window and break the seal. Frameless windows are more difficult — and more expensive — to fix, according to Reliable. The company also specializes in replacing broken windshields.

Although there is an element of inconvenience associated with repairing fogged dual-pane windows, the benefits of clear vision are obvious. And keeping the exterior looking sharp exudes pride of ownership, while protecting a sizable investment in the motorhome.


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