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Butyl Tape

Tin Kicker

Sustaining Member
Moderator
The building and commercial vehicle industries have moved from butyl tape to 3M VHB tapes and it's what Andy at Boatworks Today recommends for bedding port lights. Because it's become so widely used, availability and pricing are good. There are various thicknesses, widths, and formulations for different uses as described in their product sheet:

I still have some butyl tape to work my way through, both gray and black, but when gone I'll probably switch to the VHB.

btw - I am environmentally conscious but the EPA required changes can sure be a pain. The latest to hit me personally is that Home Depot and Lowes no longer carry MEK. Yes, it's a nasty chemical to not get on your skin but it'll cut things that acetone and other solvents won't touch.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
There is an argument for using caulk on portlights (I use butyl for most smaller fittings).

Ericson did not neatly cut the holes for the lights. There can be gaps, which caulk will fill. Also, the portlight frame may not lie flat upon the cabin house. Strong adhesion isn't important with portlights, because no outward force is anticipated. The interior frames of our stock lights are not intended as backing plates, and are mostly cosmetic. Tightening their screws hard just distorts the thin aluminum.

Either material works, and I've done it both ways. I just think caulk is more appropriate where a fitting is not going to be tightened down hard with through-bolts the way a deck fitting is. Cleanup is easy if the flange shape on the exterior cabin house is outlined in painters' tape so the excess can be peeled away.
 
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