macd
Well-Known Member
You'll so often read on these pages recommendations for bedding and bonding with silicone, most recently to a chap who was thinking of building a wet room in a wooden boat. OK, it's cheap, but it's also truly nasty. Every competent shipwright I've chatted to when the subject came up despised the stuff. It doesn't weather well in the marine environment, it attacks certain plastics, and above all it's so damn persistent. My own boat, bought last year, is riddled with the stuff, partly from original build by people who should have known better, partly from the previous owner's 'improvements' (and I know he didn't know better about a lot of things: his name is a curse on Cierzo). Much of it has failed. I won't have it anywhere near the boat.
By way of supporting testimony, see this from http://www.pbase.com/mainecruising/rebedding_hardware&page=3
Avoid silicone where you can. There are only two situations where silicone should be used and that is for bedding acrylic dead lights or plastic fittings that are damaged by polysulfides or polyurethanes such as Beckson products. Dow 795 or similar should be used for acrylic ports/dead lights. Silicone contamination of gelcoat is very, very real. It is nearly impossible to clean and remove silicone from gelcoat and auto body products intended for metal are not safe generally for gelcoat. To effectively remove silicone from gelcoat requires judicious manual cleaning then wet sanding rinsing the paper frequently to clear it of silicone traces so you don't grind it deeper into the gelcoat. To test if the silicone is gone spray the area with a misting bottle of water. If the water beads it is not clean.
A friend owned a mid eighties Catalina where the previous owner had used silicone to bed the chain plates. Even after re-bedding they leaked every year for four years straight. He had even resorted to tenacious glues like 3M 5200, still it leaked. He finally called me to discuss it and we simply masked off the surrounding areas with 3M film tape and ground and sanded away the silicone contamination. The chain plates have been dry since, lesson learned the silicone must be COMPLETELY removed before any re-bedding. If you think you've cleaned dry silicone with Acetone, De-Bond or any of the other products folks claim have worked, guess again. Over many years I have tried every chemical under the sun to remove silicone contamination and the only thing that works is a thorough manual cleaning and sanding. If you want to nearly ensure that the fitting will leak the next time you re-bed then using silicone is a good way to ensure it.
Comments?
By way of supporting testimony, see this from http://www.pbase.com/mainecruising/rebedding_hardware&page=3
Avoid silicone where you can. There are only two situations where silicone should be used and that is for bedding acrylic dead lights or plastic fittings that are damaged by polysulfides or polyurethanes such as Beckson products. Dow 795 or similar should be used for acrylic ports/dead lights. Silicone contamination of gelcoat is very, very real. It is nearly impossible to clean and remove silicone from gelcoat and auto body products intended for metal are not safe generally for gelcoat. To effectively remove silicone from gelcoat requires judicious manual cleaning then wet sanding rinsing the paper frequently to clear it of silicone traces so you don't grind it deeper into the gelcoat. To test if the silicone is gone spray the area with a misting bottle of water. If the water beads it is not clean.
A friend owned a mid eighties Catalina where the previous owner had used silicone to bed the chain plates. Even after re-bedding they leaked every year for four years straight. He had even resorted to tenacious glues like 3M 5200, still it leaked. He finally called me to discuss it and we simply masked off the surrounding areas with 3M film tape and ground and sanded away the silicone contamination. The chain plates have been dry since, lesson learned the silicone must be COMPLETELY removed before any re-bedding. If you think you've cleaned dry silicone with Acetone, De-Bond or any of the other products folks claim have worked, guess again. Over many years I have tried every chemical under the sun to remove silicone contamination and the only thing that works is a thorough manual cleaning and sanding. If you want to nearly ensure that the fitting will leak the next time you re-bed then using silicone is a good way to ensure it.
Comments?
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