You used silicone. 'Silicone is not for the marine environment. Silicone is for the bathtub environment.' --Dave Cherubini.
Avoid
all use of silicone anywhere you want to:
1. keep out water;
2. have a strong bond;
3. have easy removal, replacement AND cleanup;
4. have an attractive-looking bead.
In a marine environment, silicone has the following drawbacks:
1. It does
not hold out water.
2. It loves mold. How I know this is because of no.1. Underneath every part bedded down with silicone will be mold.
3. It is chemically slimy, leaving residue everywhere that's almost impossible to remove. Clorox will not do it; keep it off your boat entirely. Sanding it will only foul the sandpaper and spread it further afield. Acetone, MEK, zylene (duct-tape remover), all of them will fail. I scrape the fiberglass with a utility-knife blade, effectively giving the gelcoat a shave. Yes; this means remediating the gelcoat surface. That's what happens when you use silicone.
4. It provides, at best, temporary, topical strength. It's what I call 'masking-tape sticky' --it makes a physical but not chemical bond. It has little if any resistance to the kinds of shear loads you have on a boat; so it doesn't work for winches, halyard stoppers and cleats. It has even less in tensile; so it doesn't work under halyard blocks and anything that's under a vertical pull. Frankly I don't know what it
is good for, on a boat. I used GE RTV silicone (the automotive grade) to bed down my sink drains. I used it because I had some from reinstalling my car-mirror bracket on the windshield with it (the old melted in the heat). I just shy away from plumber's putty on seawater drains.
I hear all the time from boat owners who, for some reason that defies all logic, believe that 'boat products' are inordinately expensive and that anything they can get from HoDePo is 'good enough for' --
wait for it-- 'my purposes'. These people rely on anecdotal, not technical, knowledge. They don't have the facts, one of which is that polluting surfaces with silicone, which won't work for long, will cost more in hassle and money than using the right product to begin with. And it's butt-ugly. And now you have all the cleanup to do in order to get rid of the silicone residue to make the right thing work. So... will you do it right, or just do what 'most' others do and just add more silicone,
ad nauseum?
I've made a living at knowing the difference between 'boat' methods and products and 'home' ones since 1972. Here is what I know as true.
You hatch glasses are either R&H Plexiglas (a trade name, or its equivalent; it doesn't have a second 'S') or GE Lexan (a trade name, or its equivalent). Plexiglas is optically pure. Eyeglasses are Plexiglas. It shatters into very sharp shards that will slice you wide-open, like plate glass. Lexan is impact-resistant. Banks use it for bulletproof drive-in windows. It bends almost to a half-circle before it snaps (it takes a lot of strength to do this-- a big wave will not stave it in). They are not the same; and neither has all the other's properties. But they will go down with any bedding compound that is made explicitly for chemical bonds with acrylic or polycarbonate materials. To me, this means Sikaflex 295.
Some warnings about Sikaflex:
1. It is expensive, more so than 5200 and silicone put together.
2. It absolutely requires a bone-dry surface treated with its appropriate primer. This, too, is expensive.
3. It does not 'crush' well, so your handsome little squiggly line isn't going to even out as you screw down the acrylic panels. Flood the whole bonding surface with the stuff-- if it's a warm day try smoothing it out with a 1" plastic putty knife (you'll throw this away rather than clean it). Otherwise everyone will see through the Lexan and see your pathetic attempt at a squiggly line (experience talking!
).
Benefits to Sikaflex:
It absolutely holds well to acrylic. It will bond fiberglass and other things to it as well; but none of those other things works with the acyrlic so this is the default for everything but maybe holding on the keel and underwater stuff. Most of Houston ('city of glass'; it's actually Lexan) is held together with Sikaflex (according to Sika).
Read the info on their website and also at Defender.com.
In olden days we (the industry) bonded Plexiglas with 5200. One trick was to sand the surfaces to about 80 grit, providing greater gripping surface and adhesion. This always worked. It didn't when I did this to my boat. I went with Sikaflex, which now leaks because I didn't use the primer. The rumor (from 3M) was that 747 jetliners don't use screws to hold in the windows-- only 5200 (imagine! --well; the cabin pressure holds them in).
Learn from this. Get the right thing and do it right. And go put the silicone in the garden shed where it belongs (if even there).
