The next, or third step, in prepping the trim ring, is to apply the sealant. Do not skimp on sealant! Sure it will squeeze out and you will waste a lot of it but it's important that you have enough in there to seal the entire face of the trim ring. I also doubled up around the studs by applying the sealant on top of the butyl rings.


For this task I used 3M 101 which is a one part polysulfide. It has a bond strength of about 140 PSI and an elongation at break of over 400%. I have been using 3M 101 or Sikaflex 291 a lower bonding (220 PSI) single part polyurethane sealant for years and had great success.


I chose to use 3M 101 polysulfide because it's easily removable in the future, never hardens as it's what they used for the UV exposed seams in teak decks. Polysulfides are quite UV resistant by nature, without added UV stabilizers like the polyurethanes need. Even the lowest adhesion polyurethanes like Sikaflex 291, at 221 PSI, offer more adhesion than is necessary in a mechanical fitting which a port is.


NFM recommends, in their instructions, Sikaflex 295UV, a one part polyurethane. The problem I have with 295UV is this. 295UV bonds at 450 PSI (adhesion strength per square inch) which is 150 PSI more than other polyurethanes such as Sikaflex 291 at 221 PSI and 3M 4200 or 3M 4000UV which are both 300 PSI. Anyone who's ever used 3M 4200 knows how difficult a 300 PSI product is to remove let alone a 450 PSI product like Sikaflex 295UV.


I know the owners of NFM have the utmost confidence in their ports but at some point they WILL need to be removed or re-bedded and with a 450 PSI adhesion it will be difficult, quite difficult. Heck, it's even hard to remove stuff bedded with 3M 101 at 140 PSI.


EDIT: 3M 101 has been discontinued. If doing this project over again I would use gray Bed-It Butyl tape and avoid the entire marine sealant process.