I want to replace the plexiglass, (which are cracked and terribly scratched) in our two overhead hatch covers - the largest being 24' X 24". The material will be seated in a teak frame. I've search the archives, but can't find a convincing argument for using plexiglass over the more expensive lexan. Which is preferred and what is the best product to set and seal? I think it currently has silicone around the edges. Any advice is greatly appreciated.
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My 2 cents
Marcia, Lexan is the stronger choice and virtually unbreakable However, it is also much softer, i.e. it will scratch way more easily. Unless your hatches will be taking big waves in direct hits, or if you'll be consistantly dropping stuff from the masthead (or getting into gunfights?)then the extra strength won't really be needed. I don't have the strength numbers in front of me but a thick enough piece of plexi (more than 1/4"!) should do fine for 24"x24" span under normal usage. I seem to recall reading somewhere that the darkening/yellowing is about the same for either material, though plexi may start crazing sooner? I've also read that silicone is the best for seating material. It's not the strongest sealant but other caulks will yellow with UV though regular silicone, apparently even that which is behind the plexi. Also, if you have any mechanical fasteners passing through the plastic (screws, bolts) make sure that the holes are oversize to handle the shrinkage & expansion of the plastic material. cheers, Craig Ranger 28
Marcia, Lexan is the stronger choice and virtually unbreakable However, it is also much softer, i.e. it will scratch way more easily. Unless your hatches will be taking big waves in direct hits, or if you'll be consistantly dropping stuff from the masthead (or getting into gunfights?)then the extra strength won't really be needed. I don't have the strength numbers in front of me but a thick enough piece of plexi (more than 1/4"!) should do fine for 24"x24" span under normal usage. I seem to recall reading somewhere that the darkening/yellowing is about the same for either material, though plexi may start crazing sooner? I've also read that silicone is the best for seating material. It's not the strongest sealant but other caulks will yellow with UV though regular silicone, apparently even that which is behind the plexi. Also, if you have any mechanical fasteners passing through the plastic (screws, bolts) make sure that the holes are oversize to handle the shrinkage & expansion of the plastic material. cheers, Craig Ranger 28
Ditto what Craig said; make the holes oversize
This is more important than whether you us polycarbonate (Lexan) or polystyrene (plexiglass). Lexan scratches more easily but doesn't yellow and craze as soon. Plexiglass is harder but it starts to craze and yellow sooner in sunlight. Since Craig and I are in beautiful BC, Canada, sunlight is not as significant for us as it may be for you. I helped deliver a boat from Whitestone, Va. to Seattle once, leaving Norfolk in August, and one thing I remember is sunshine stronger and hotter than we ever see here.
This is more important than whether you us polycarbonate (Lexan) or polystyrene (plexiglass). Lexan scratches more easily but doesn't yellow and craze as soon. Plexiglass is harder but it starts to craze and yellow sooner in sunlight. Since Craig and I are in beautiful BC, Canada, sunlight is not as significant for us as it may be for you. I helped deliver a boat from Whitestone, Va. to Seattle once, leaving Norfolk in August, and one thing I remember is sunshine stronger and hotter than we ever see here.
Marcia, I rebuilt all of my hatches.
On our fore deck I was replacing Bomar lenses. That meant the new stuff had to be as thin as the original. That meant Lexan. I followed Bomar's instructions. There are no screw holes because the lenses are held with the caulk. And that is; (Drum-roll) GE UltraGlaze SSG4000AC (Accelerated Cure), Structural Glazing Sealant. How's that for a name? Google it and find a local dealer. I still have a tube. I only needed half as much as I bought. And for glazing, forget about other stuff. Silicone is impervious to environmental damage. No silicone has ever failed from UV exposure,,,,EVER! How can I say that any stronger?
On our fore deck I was replacing Bomar lenses. That meant the new stuff had to be as thin as the original. That meant Lexan. I followed Bomar's instructions. There are no screw holes because the lenses are held with the caulk. And that is; (Drum-roll) GE UltraGlaze SSG4000AC (Accelerated Cure), Structural Glazing Sealant. How's that for a name? Google it and find a local dealer. I still have a tube. I only needed half as much as I bought. And for glazing, forget about other stuff. Silicone is impervious to environmental damage. No silicone has ever failed from UV exposure,,,,EVER! How can I say that any stronger?
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