[C320-list] Sealant/caulking

[Dave Hupe]

I have used butyl tape, Dow 795 and several 3M sealants.......all this summer after having purchased our boat this April.
I rebedded my center cabin Bomar hatch with butyl tape which worked very well.  However, it is hard to make 90 degree or curved corners.  I slightly overlapped the tape where I did the corners.  You need to be careful not to make the overlap areas too thick if you can't tighten hardware down enough to make sure everything seals when compressed. You might also be able to butt the tape tightly at transition points, since it should squeeze together at the butt edges and seal. 
I think butyl works good when you are dealing with smaller wood/sheet metal mount hardware that easily penetrates the tape during mounting. However, where you have large bolt type mounting hardware, you can't just lay the tape over the holes and punch the hardware through it.  So, it becomes tough to deal with properly sealing around the hardware.  That is why caulk type sealant may be better in such circumstances. 
I have used 3M products several times and am upset when I use very little and the tube hardens very quickly thereafter. It also dries essentially hard and can dry out over time. The Dow 795 sealant adheres extremely well, stays flexible/rubbery after curing, and has very good elasticity (so it can accommodate future "movement"/flexing without leaking).  The partially used tube can be sealed and it stays good for quite a while.   
Dave Hupe
1994 Cat320 (hull #32)
Holland, MI