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  Topic Review (Newest First)
01-26-2009 01:24 PM
lbdavis Check out this report from our esteemed member, Maine Sail.

Good enough for Maine Sail, good enough for most.
01-26-2009 01:11 PM
Plastic and bedding compounds redux

I just thought I'd re-open this question, since it's never really been resolved.

We are re-installing some Beckson plastic-framed portlights, and the manufacturer says "only use 100% silicone." Since silicone skins over in 5-10 minutes, our surveyor says the beginning of the bead will skin over before you're gotten the stuff applied to the entire surface. It is destined to fail.

So will polysulfide actually degrade a Beckson plastic portlight?
What about polyurethane?
Will a polyurethane/silicone blend, like Boatlife's Life Seal, work instead?
Lastly, what about butyl rubber? It works OK for temporary fixes, but can it be installed well enough for an offshore, water-tight seal?
05-19-2004 07:50 AM
Effect of Polysulfide and polyurathane on plastic ports

Hi Dennis,

For the last 29 years we have used many gallons of 2-part Thiokol (Paraseal, no longer made) on Plexiglass ports and hatches, on ABS, PVC, CPVC, and other plastics, metals and wood on our boat, from keel to truck, stem to stern. ALL IS STILL PRISTINE, after 27 years of sailing, tropics to sub-zero.

Since Paraseal was discontinued about two years ago I have just completed some research in order to find a new supplier, and settled on AC Tech AC240B2. AC Tech and Rohm & Haas, the inventor of Plexiglass, both agreed with my use of Thiokol. AC240B2 is aircraft grade.

We tried some small projects with Boatlife 2- part and were very disapointed with the poor adhesion and mixing unfriendliness, including the insistence by the manufacturer that you MUST mix the whole can in one go!

You can check the specs of AC240B2 (2 is the cure time denominator) at

All the best - Peter
05-02-2004 11:51 AM
Effect of Polysulfide and polyurathane on plastic ports

Alright, thanks. Guess it will remain a mystery for now.

05-02-2004 02:13 AM
Effect of Polysulfide and polyurathane on plastic ports

Windship (Dennis):
You''re correct of course (Life Caulk = Polysulfide); I should have said "Life-Seal" (Polyurethane + Silicone).
At 27 years old, we''d be talking late 70''s
I encountered Polysulfides, Polyurethanes, and Silicone’s in the automotive & glazing industries in the early to mid 1960''s.
I know that Thiokol (now Morton-Thiokol) developed the Polysufides during WWII.
I’m not certain when the hybrids (Polyurethane-Silicone, Epoxy-Poly'') were first introduced.
Interestying ...
05-01-2004 04:34 PM
Effect of Polysulfide and polyurathane on plastic ports

Yeah, I can''t figure it out either however I am suspicious of this thing. Maybe I''ll do an experiment on an old port I have laying around.
Were hybrids around back then?
Life-caulk is polysulfide.

05-01-2004 03:02 AM
Effect of Polysulfide and polyurathane on plastic ports

I can''t explain your excellent experience /w 5200 on plastics - except to wonder if the bedding might have been something other than pure polyurethane (5200).
Perhaps Life-Caulk (or some other) hybrid?
04-30-2004 11:58 AM
Effect of Polysulfide and polyurathane on plastic ports

Thanks for your response.
Yeah, we''re pretty smart here I guess and I''m well aquainted with the different types of sealant/adhesives and their applications but that wasn''t the question.
The reason I asked the question is last week I removed a port in a boat that was installed 27 years ago. It hasn''t leaked in 27 years and it was bedded in with 5200 and the port is still in perfect shape.
If both polys are supposed to attack plastic ports, why did this beddidg job last so long and why is the port(and the rest of the ports that still aren''t leaking)still in perfect shape?

04-30-2004 02:58 AM
Effect of Polysulfide and polyurathane on plastic ports

Polysulfides & Polyurethanes will adhere to metal, glass, fiberglass, wood, or any combination of these. Do not use either on PVC, Acrylic (Plexiglas, Lucite), ABS, or Polycarbonate (Lexan) plastics.
Although the modalities are (more or less) opposite, both “Poly” products are incompatible with the above “plastics” (excluding Nylon, Dehlrin, Marelon, or Epoxy):
The solvents in polysulfides can leach the plasticizer from these plastics and cause them to harden and crack.
Solvents, leaching from some plastics, can react with polyurethanes and cause a failure of the adhesive sealant compound.
For an adhesive seal of plastic components, select a silicone/polyurethane or epoxy/polyurethane hybrid.
Never use any caulk that is catalyzed by acetic acid (i.e., smells like vinegar) on acrylic; it will cause crazing.
Silcone has little if any adhesion. It is merely a gasket material, but an excellent gasket. It will not attack plastics, but may cause crazing on acrylics.
04-30-2004 02:20 AM
Effect of Polysulfide and polyurathane on plastic ports

Could be that the Sailnet membership are smart enough to have avoided the problem?
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