What sealant/adhesive to use on each project


Sep 8, 2006
san clemente
"I'm in the market, as it were" - Jack Sparrow
Just got an older boat need to do a little work on it. there are so many brands and types of sealants/adhesives out there and each one works best for different things, some claim they can be used on everything. need to know what type to use on each of the following projects: (note do not care about looks at all)

Flush Mount Rod Holder install (leaning toward 3M 4200)
fill small transom holes from transducer mount
fill large holes in transom from kicker motor mount
seal seams around existing through hull fittings
install new transducer mount
seal bow hook U-bolt

appreciate all the help I have received from the BD community with fishing a gear advice, the boating aspect is new to me so my apologies for so many posts.
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fly liner

I Should Upgrade My Account
Apr 10, 2009
hemet ca USA
21' crystaliner /15' prowler
4200 for sealant, 5200 for permanent. Small holes in the transom, remove old screws, if you want, you can chase the hole with a drill bit to clean it up. Depending on the size of the hole ,get some tooth picks, skewers, golf tees ,or wood dowel of appropriate size.measure the depth of the hole cut them about an 1/8" short. Slightly chamfer the gelcoat around the hole, either coat your wood pin or squeeze sealant into the hole or both. Push the pin into the hole, and put a little dab over the hole. For the kicker mount basically same process, except you should mix up some resin and coat the inside of the holes before inserting the dowels , or just goop a bunch of 4200 inside.. your bow hook.remove , clean , replace if needed the backer piece (possibly wood) re seal it , very well.

Your thru hull fittings can be a safety issue, might want to take the time to remove them, clean the surfaces and reseal them.

This is all just my opinion, other members will surly have more experienced methods. But these are my suggestions
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Dream to fish

Deck Swaby
Jul 25, 2009
Hell, CA
20' Beachcraft Cuddy
I couldn't think of any place on my boat where I would use 5200 for "Permanent". 4200 is also rated for below waterline use so I'm using that. For all the stuff like rod holders, 4200 is fine and even 3m MARINE silicone should be fine as well. Transom holes, I filled with polyester resin/cabosil or epoxy/cabosil. Add chopped glass if the holes are bigger than 1/4" or so. You can apply gelcoat over the poly resin but probably won't get away with doing that over epoxy unless it's a small hole and you sand the gelcoat off of a larger area and re-apply. If the gelcoat is adheared to 2" around the hole, you may get away with spanning a 1/4" piece of epoxy. That's what I'm doing...you're mileage may vary.
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Apr 3, 2019
Costa Mesa, CA
Always changing
Above waterline - 4200. Below waterline - epoxy (or 5200 if you have to) Anything larger than an 1/8" hole that's exposed to water, fill it with epoxy
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May 13, 2004
Long Beach and points due west
Bob Ballew
2520 Parker with twin 200 Yamahas
Tape off each area with painters tape (Frog tape is best) to get nice straight finished lines, allowing you to smooth out the seam with a wet finger and no smeared overlap....
...some boat yards do everything with "Boat Life" sealant, which seems the same as 4200 but, cheaper in price...Best 4200 price was at Lowes or Home Depot if I recall correctly...
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