Caulking Interactions with Insulated Glass Units

Questions exist about whether silicone caulking can degrade the sealing material in some insulated glass products. January 20, 2011

I am installing 3/4" thick insulated glass units in exterior doors. The glass stop will be glued and nailed onto the inside face of the doors. Is there a problem using clear 100% silicone to bed them in? The doors and door stops have been spray primed (glue surfaces taped off) and will be brush painted on site after installation.

Forum Responses
(Architectural Woodworking Forum)
From contributor D:
I see no problem. Millions of units out there have a silicone of some type for caulking and it will outlast the wood. Make sure you have squeeze-out, and don't get the stuff on your hands and handle the door, otherwise your silicone fingerprints will inhibit paint adhesion.

From the original questioner:
Thanks - what is your solvent/method of choice for cleaning the silicone squeeze-out?

From contributor J:
It matters. I have been warned for many years not to bed standard insulated glass with silicone, as it breaks down the seal like a solvent. The manufacturer should be able to say if silicone is okay or not. I ordered insulated glass last summer, and the maker was glad to provide silicone compatible insulated glass, as opposed to the standard stuff that is bedded with urethane or some such.

From contributor D:
I've never seen or heard of solvent used to clean up. We've always just let it dry and then used a razor blade to clean it off. Most manufacturers leave the squeeze-out, and we do as well, except on high end doors where you want the cleanest look possible. Unless you have some special coating on the glass (like "self cleaning," which is a treatment that uses the properties of static electricity to repel dust particles), I've never seen an issue with silicone. Perhaps it may interact with butyl rubber swiggle over time and outgas, but you shouldn't have any caulk touch the swiggle anyway. Your glass should sit on a bed of caulk, not in it. A bead half inch wide by eighth inch thick is sufficient to bed onto. Some caulks have small plastic beads imbedded into the mix which create a stop-gap. In other words, you can press down as hard as you can and still have a small assured layer of silicone.

As an aside, we use a dark colored caulk on doors. On close examination at eye level and at an angle, with clear caulks and thick IG units, you will see the bare wood in the rabbet, adjacent to a stained or painted finish. A dark caulk, same color as your swiggle, in my opinion, looks better.

From contributor V:
I agree with contributor J. We use Dow Corning 1199. It is a neutral-cure RTV sealant available in all of your favorite colors.

From contributor D:
We are a manufacturer of both IGUs and architectural millwork, including windows and doors. A swiggle made by Truseal in fact does react when in contact with silicone. No issue at all, though, if your unit is properly bedded, as it should never touch the swiggle. Truseal will void their warranty, I am told, if it is discovered to be in contact with silicone. I am investigating further to see if any other swiggle brands react with silicone.
We are using Trem Glaze 1600 in our doors and have earned a DP rating of 80 in wind tunnel testing, and used silicone for a number of years with the same results.