side-trim sealer: Petroleum jelly / clear dielectric grease

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Jon March

I know people have mentioned dum-dym type nonhardening "bedding compound" or even silicone caulk to seal the side trim screws - both of which are a good idea to prevent water intrusion INTO the car

but this is a different question:

water seems to inevitably get trapped UNDER the side trim, creating rust - so i wondered if a clear coat of something like vaseline under the side rubber to prevent water trapped there from attacking the paint -
..but im not sure if vaseline is inert enough to not soften paint. i THINK its safe...makea call to cheeseborough ponds.

Then i read that its melting temp is 100 degrees - which sheet metal in the sun far exceeds; it would drip out and evap away.rats.

WD40 is "water displacing" - but it would drip out too...

So maybe a thin line of silicone caulk all around the edge of the trim - to try to prevent water from even getting IN... but that would create an area for condensation to be trapped and not be able to escape - possibly making it worse!

>> so maybe just a line of caulk (or dielectric clear grease sealer(higher melting temp)...along just the TOP edge - to sort of form an air bubble barrier under the side trim to help resist water intrusion up there - but leaving the bottom edge open to drip and evap out....

you laugh, but this is at least based on pretty valid logic...i think.


Active Member

I used a small dollop of a clay type of sealant where each screw goes through, but a bigger problem for Amphicars is the cardboard kind of stuff they used on the inside, between the outer sheet metal and the internal bracing. If this stuff is allowed to get wet, hopefully not often, it soaks up the water and holds it against the inside metal. I've seen this kind of damage on cars that spent years in a field or have somehow taken on a lot of moisture. Surprisingly, those Amphicar dum-dym things actually work quite well where they are used and I only put a bit of sealant around the screws to prevent water from getting to the inside of the hole they are used at. Generally, your outside paint will protect the sheet metal pretty well but I wouldn't try to block the area around those side strips. I don't think anything will completely stop the water or moisture and it better to let it get out rather than seal it in behind the side strips.

In a related matter, the horizontal rear bumper rubber is good at holding water against that rear body seam and is the reason that there is so much damage under that rear bumper area. My fix for that, as well a serious undercoating under the top paint in this area, is to drill holes along the lower side of that bumper rubber. There is no way to keep water out of there so the best thing is to allow the water to drain out and air to get in and dry things out after swims. These 1/8" holes are invisible unless you are laying on the ground at the back of the car and looking for them.

John Friese
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