[Public-List] Holding Tank Cover

[James Allocco]

I have hull #565 with a holding tank formed by the liner under the sole
boards  The tank has an aluminium cover.  For the past several  years there
has been some fumes leaking out around the cover. Not want to remove the
cover 2 years ago I laid down many beads of silicone caulk around the
perimeter of the cover extending 1 1/2 " in from the sides. The caulk has
lifted off of the cover due to corrosion (white chalk) formed between the
caulk and the Alum. Recently I removed the cover and found the discharge
tube badly corroded.  The top surface of the cover had considerable
oxidation. I had a new cover fabricated.

Before I install the new cover I have two concerns.

1. What kind off caulk to use under the cover that will be least affected by
the chemical environment. I plan to use a nitrate based chemicals. I don't
want to use 5200 in case I ever need to remove the cover.

2. If corrosion can occur between the caulk and cover, the seal will be lost
and fumes will again escape. Could I or should I coat the underside lip with
epoxy or other type of coating before caulking and riveting in place?

Thanks
Jim Allocco #565

 1268590278.0