eightamrock wrote:Source of the post
Also, not sure how to calculate the amount of desiccation I need. Anyone know the formula?
Depends on what type of desiccant you use!
Silica gel seems to be the most common, so I'll assume that's it.
For silica gel, I normal use 200 grams per cubic meter of air space in the window cavity. Measure size of glass pane (width, height) and distance between glass panes: Multiply all three to get the volume. If one pane is bigger than the other, use the dimensions of the largest one.
It's OK to overdo it a bit with the quantity of silica gel, but don't go too far, or the air inside will be too dry: the wood of the window frame might dry out and crack after a few months / years. Use the right amount, and up to about 30% more, but don't go too crazy. And do make sure it is dry and dehumidified, before you put it in! What I do is to "cook" it for several hours, to make sure it is perfectly activated, before putting it in and seal up the windows. In other words, if it is the type that changes color, make sure it is the right color before you put it it! Either blue or orange, depending on the type. But never pink or green! If it is the wrong color, or if it is not colored at all and you don't know if it is dry or saturated, it probably needs "cooking". To do that, I heat it in an oven set to about 125 °C (about 250°F) for several hours, then put it in the cavity and seal the glass in place as soon as possible afterwards. It's OK for it to sit for a few hours while it cools, and while you get things in place, but don't let it sit for days, as it will start adsorbing moisture from the atmosphere and already be partly saturated by the time you put it in.
Silica Gel is pretty inert: it's actually similar to quartz or sand, chemically, so you can put it on or in pretty much anything, to hold it. Those labels that say "Do not eat! You will die horribly!" or whatever, that you see on the packs of silica gel in cameras, shoes, pills, handbags, etc. are because of the additives that they put in so that it changes color when dry / damp: That color-change chemical stuff is poisonous, but not the actual silica gel itself. It's no more dangerous than sand. If you got the stuff that does not change color, then you could use pretty much anything you want to make the "tray" to hold it. If you got the color-change stuff, then I'd go with plastic: you can find plastic "profiles" in hardware stores, such as Home Depot, and use that to make small trays to hold it, then glue and staple those to one side of the frame gap. Don't use metal or wood for the color-change stuff, as there might be reactions with the color chemicals.
Spread out the silica gel as much as you can in the "trays", to get maximum surface area exposed to the cavity air.
NOTE: The above only applies to silica gel! Other types of desiccant are different. Some cannot be "cooked", or need different temperatures. All need different amounts per unit volume of air.
- Stuart -