[quote=toddelozory]Ed sealed insulated units are designed to increase the insulated value of the glass component of the wall. There are dual seal unit, where the primary sealant, usually butyl tape, seals the space between the glass and the aluminum sirspace; the secondary sealant adds a structural bond to the unit, either silicone, polysulfide, polyurethane, etc. The water vapor transfer rates for each sealant are different, butyl has the lowest, hence it's use as a primary sealant. There are also single seal units available, The dual seal units are used primarily in commercial applications. There were a lot of construction projects that incorporated two sided butt glazing, only two of the units edges were captured by framing, and there were some projects that used 4 sided butt glazing. Those buildings have the appearance of all glass, no aluminum. The structural components were added to keep the outboard lite of glass on the buildings.
The glazing tapes are used to seal the unit into the frame. They would not be recommended for marine application. The back bedding tapes are generally foam with double face adhesive. The glass stop applies enough pressure to compress the tape sufficiently to keep the outside air out.
The use of gas filling is only widely used in colder climates. Argon and Krypton are both colorless and oderless. How do you know there is any gas inside the unit? If the sealants are semipermeable, why does the insulating gas stay in the unit? In the sunbelt, the units are filled with ambient atmosphere. There is a dessicant, a molecular seive filled into the aluminum airspace. The purpose of the dessicant is to absorb any moisture or water vapor that enters the unit. When the dessicant reaches it's saturation point, the unit will fog. Once there is sufficient watervapor inside the unit, the organic seals deteriorate. Generally along the bottom edge, because that is where the condensation settles. If you catch the failure soon enough, you can cut the unit apart and reseal it. Most of the time, it is far less expensive to just buy a whole new unit. The glass units in my house are made with a reflective azure blue glass, so when I see the unit starting to go, I pull it our, cut it apart and reseal it with butyl.
The biggest cause of seal failure is exposre to excessive amounts of water. The window, and glazing systems are designed to channel the intruding water away from the glass through the use of weep systems and setting blocks. Water seeks the path of least resistance. Once inside the glazing pocket, it will attack the sealant, if the unit's edge is resting on the sill. The stting blocks elevate the edge to allow the water to weep out. Other cause include chemical reactions with other sealants; an acetoxy cure silicone would be a poor choice for a toe bead with insulated glass. Before a glazier installs a large scale project, he should check for sealant compatability. Another common cause is using setting blocks of the wrong durometer. The setting blocks are made of rubber or lead or plastic. If they are not placed correctly, they can cuase the unit to shear, or apply too much pressure to the sealant and push the airspace into the vision area.[/quote]
