Hi Drew,
Although I'm not replacing the portlights now, I am interested in using Dow 795 to adhere the existing portlights.
This article by Don Casey in Sail Magazine describes a method using Dow 795 and VHB tape:
http://www.sailmagazine.com/diy/mainten ... ortlights/
I have not yet found directions from Dow Corning that describe specs for this use.
Casey suggests that the thickness of the VHB tape, 2.3mm or approx 3/32", gives enough space for the sealant. Perhaps that is good enough for a sealant role, but not enough space for a bonding role for the Dow 795?
Does the VHB tape defeat the bonding and thermal expansion advantages of the Dow 795? I'm thinking the VHB is closer to 5200 with respect to permanency/replacement.
The tape serves as a backer material for the caulk. I like this better than the rubber bumpers that I believe were the original spacers. The tape will help ensure that the caulk is optimally located for bonding and edge sealing, as opposed to migrating inward toward the center of the portlight.
I'm leaning toward using a UV stabilized tape of TBD dimensions as a backer/spacer, the original screw and trim washers for initial clamping, and Dow 795 with a concave edge treatment. I'd remove the screws after appropriate setup of the caulk and fill the holes with Dow 795.
So, I'm interested in feedback, positive and negative. I'd like to know what the optimal spacing to provide bonding of the portlights to the fiberglass is.
I did find a neat technique for tweaking the nozzle on the caulking tube in order to better guide the caulk into the tight spaces. Simply cut the nozzle to the needed opening, then crimp the nozzle end with pliers to create a rectangular shaped end that fits between the adjacent portlights and edges.
Thanks,
Joe Mc