Marine Sealant vs Epoxy
- Thread starter Randy18540
- Start date
- Status
Butyl tape is great stuff but, my entire boat was sealed with it from the factory 30 years ago and my chain plates are still dry, as is my hull to deck joint. I do not use butyl however in applications where there will not also be mechanical fasteners. I am going to guess you are talking about the acrylic to the hatch frame? If so I'd use Dow 795 for that.
And Don has given some questionable advice over the years, namely his "make a gasket tighten twice" method of bedding and his statements about all silicone needing fasteners are just not true and you don't have to look far to see this...
Silicone can be a structural adhesive and is in use world wide across many industries as such. There are many grades of silicone so to lump them all together is also poor judgment on Don's part.
Silicone holds windows in sky scrapers and products like Dow 795 or GE SilPruf are holding millions of port lights onto boats and hatch lenses into hatch frames, on boats throughout the world using no fasteners.
Perhaps Don should do better research before making factual statements in books read by boaters and believed as gospel. It is not always true that silicone can not be used as a glue to hold prouducts such as ports and lenses to boats. Lewmar, Bomar, Hunter, Catalina, Adkins & Hoyle, Goiot and builders like Beneteau, Hunter and Catalina to name a few all use silicone to hold products together with no fasteners..
And more often than not this Don Casey method results in leaks around screws that turned after the sealant cured.This creates a great path for water to leak around the screws. Most marine plastics experts strongly advise against the use of screws in acrylic port lights. Tony D'Andrea, who is the Nigel Calder of marine plastics, strongly cautions against this.
It's no problem to use the screws until cured but he advises to remove them once cured and to fill the holes with the silicone used. These plastics expand and contract at a greater degree than the GRP and can cause the ports to crack at the screw holes unless the holes are made considerably bigger than the screw wire size to accommodate movement. In small short ports this may not be an issue but the longer the port light the more expansion/contraction along its length.
Does the plastic hatch have good mechanical fastening to the hull—ie, is it through-bolted properly? If not, then you will probably want a sealant that has some adhesive qualities, which butyl rubber tape does not. However, if the hatch is going to be properly through-bolted, then I see no reason not to use Butyl Rubber Tape. However, I would highly recommend using the grey, not the black...the black can be very messy to clean up. 
I appreciate the advice.
In fairness to Don, I think his comments re silicone are meant to refer only to the silicone sealants available in the marine retail chain.
On our boat, since we were remounting, the holes already existed and were oversize, and all the screws have flat washers, so, hopefully I won't encounter cracking or leaks.
With flat washer and over sized holes you should be good. It's only if you drill tight fitting holes then countersink the heads into the acrylic that you'll likely encounter issues on smaller ports..
- Status