Adding to
@dLj 's comments which are right on the mark, maybe one or two additional comments :
the PO installed it with 5200
One problem here is that 5200 is not silicone, its polyurethane. Contains no silicone.
Years ago I was concerned about replacing the lens of a framed hatch lens. The frame had a few places where it was near impossible to remove the remaining sealant and of course the sealant stuck like
to a blanket (or in this case an old frame).
I wrote to 3M and, as often seen back in the good old days, they answered me the next day in great detail :
Dear Ralph,
This is a follow-up message from Dow Corning to your recent inquiry. Yes, 795 will adhere to old 795 as long as the old cured 795 is clean, dry, and frost free. Below I have provided information that discusses the removal and replacement of cured silicone sealant and our recommendations.
Removal and Replacement of Cured Silicone Sealant
A properly designed and installed silicone joint will typically last 20 years without need of replacement. In instances where the joint has experienced mechanical or other damage and replacement is required, follow the procedures below. Assess the problem with the joint.
1. If the sealant is cured properly and performing application but its appearance is poor (i.e., due to improper tooling), then cleaning the sealant surface with a solvent and recapping the joint should be sufficient.
a) Clean sealant with a solvent (i.e., xylene, toluene) to remove dirt. Allow solvent to evaporate.
b) Remask the joint.
c) Apply a thin bead of fresh sealant over the cured sealant.
d) Dry tool the sealant.
e) Remove the masking material.
2. If the sealant is mechanically damaged and a recapping will not improve the joint appearance, then remove the section of old sealant and replace it.
a) Cut away the old sealant. If excellent adhesion to the substrate is still maintained, then leave some sealant at the edges of the joint (up to 0.08"/2 mm thick).
b) If adhesion to the substrate is poor, then remove sealant down to the substrate and clean the substrate and recondition if necessary (i.e., clean with xylene and prime with appropriate primer).
c) Mask the joint.
d) Reapply the sealant. (If resealing does not occur on the same day, the joint will have to be recleaned using a solvent such as xylene or toluene before applying the fresh sealant.)
e) Dry tool the joint.
f) Remove the masking material.
g) Check adhesion after the sealant has cured for 7 days.
Thank you for contacting Dow Corning. If I can be of further assistance, feel free to contact me.
Best Regards,
Mary
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Basically, it looks like nothing adheres to silicone except silicone. However, being from Missouri, I decided to test it. A thin wipe of 795 on on a piece of glass and let it sit for a few days until set. After a few days, a small blob of 795 on top of the first 795 and let it set for a few days more. There was no way in hell the blob was coming off the older 795. Good enough for me even though the 795 underlay was not years old. No leaks to date. Try a test on your lenses and frames. Something's not quite right.
Do not use butyl tape on the windows :
Butyl does not really adhere to the surface, it seals against the surface.
Exactly. Given enough time, the lens will fall away into the cold, cold sea without something to hold it in place. It has no muscle for holding but relies on nuts, bolts, ahd screws to provide a superlative seal. Use 795 as all the boat manufacturers do "
