Which Caulking to Use??

[Ewlon]

I'm ready to caulk my sailing dinghy. I've put cotton into the seams and now want
to top that off with caulk, then paint it. I was going to use Boat Life boat caulk, but
someone told me it has a tendency to pull away from the wood on one side of the
seam as it dries. The label says it never gets hard, but remains flexible to expand
and contract with the joint.

Any comments or recommendations? :confused:

[Bob Cleek]

Try Interlux topside seam compound. Stay away from the polysulfide seam compounds. Particularly on top of cotton in a traditional seam. While adhesion with polysulfides can be improved remarkably by priming with CPES, they are very messy and hard to work with and fair. (You can't sand them for beans.) More significantly, when it comes time to patch up a spot here or there, proper seam compound is easily reefed out and replaced. Rubber seam compounds are much harder to reef out and result in mangled bevel edges. Costs a lot more, too!

[Scott Rosen]

Check out this discussion for all you never wanted to know about seam compound.

http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=003684

[Ewlon]

thanks for the input guys. Wow, what a thread--really all you ever wanted to know.

As this is a dinghy on a trailer when it's not occassionally sailed, what do you recommend?

And let's don't fight.

[Bob Cleek]

Ewlon, in response to your e-mail note, which may have been sent before Scott gave you the "mother of all seam compound threads," let me say this about that...

What you found in the seams originally was likely white lead putty, or perhaps even Interlux (or equivalent) topside seam compound. It does dry out and crack. Nothing lasts forever in this game. Fortunately, that property makes it also easy to clean out and replace, decidedly unlike the rubbery polysulfides.

A truly flexible seam compound that provides watertight integrity is the holy grail of wooden boatbuilding... but it don't exist. Your boat was likely built using sound practices and is entirely suited for the use intended. It may not have been intended to live on a trailer and only be soaked a half dozen times a year. Remember that back in the wooden ships days, a regular routine aboard every ship was towing the small boats astern to keep them swelled up and tight. Just imagine what towing her on a trailer 100 miles in 100 degree weather to take that nice day sail is going to do to your seams! Really, traditionally built wooden boats aren't the best for trailering and no magic goop will stretch enough to compensate for the radical cyclic plank swelling and shrinking when boats are stored dry for long periods or, God forbid, towed in hot wind down the freeway. You are probably best off using the standard seam compound, rather than rubber stuff. Keep her as humid as you can and use her as often as possible. If she really starts to open up, maybe she isn't the best boat for your purposes and you might consider trading her for a boat that doesn't depend on swelled wood to stay tight. That's where cold molding and plywood and epoxy come in. It's just the way it goes. Skiers who live in the desert have similar challenges. Sometimes you just can't get there from where you're at.