View Full Version : Opinions needed on polysulfide as seam compound

09-23-2006, 08:52 AM
Has anyone had experience they'd like to recount about using Interlux polysulfide in tubes as seam compound during refastening process? Planks still have a pretty high moisture content even after 10 months out of water.

09-24-2006, 10:01 AM
I have a 40' S&S sailboat, Nevins built, mahogany planked, that a previous owner puttied the seams with "Lifecaulk" polysulfide. The problem is that the stuff stays so flexible that paint won't stick to it. So toward the middle of the season, the paint cracks off the seam compound, then water starts getting in behind the paint on the planking, and getting it off. I worked for years to get rid of this stuff and replace with with conventional seam compound. It adhered so well and was so flexible that it was nearly impossible. Then I discovered an electric hot-knife tool specially made for the purpose. It creates clouds of noxious fumes, otherwise works like a charm.
I'd suggest that at the VERY LEAST you try caulking a couple of seams with the stuff, then see how paint sticks to it. Then try to figure a logical reason why this stuff is better than plain old Dolfinite.

09-25-2006, 07:04 AM
You may want to search old threads for information on this - seems like there was a heated debate a couple of years ago ... involved Scott Rosen, if memory serves. Good luck.


09-27-2006, 05:37 AM
Thanks seo and bark for the information. The test area sounds like a good idea and I'll also check the archives for the discussion

09-27-2006, 08:04 AM
I would not use the polysulfides or polyurethanes as a caulk in your plank seams. The reason being that those compounds set up "relatively speaking" hard over the years. Your wooden boat was engineered & built to flex a little. Your boat will most likely end up slowly tearing itself appart as the planks expand and contract with these hard seam compounds in between them.
However, that said, there is a case where a wooden boat maufacturer has use a polysulfide and that was Chris Craft, but only in their wooden lapstreak sea skiff line of boats, as they were particularly engineered and built to use polysulfide like caulk between the plywood laps.
There is tons of information/threads on this subject in the forum - so do a search on it.

Dan McCosh
09-27-2006, 09:48 AM
Polysulfide is a kind of synthetic rubber. Depending on its formulation, it sets up much like a strip of neoprene in the seam. It's adhesion is medium--normally requiring some primer in the seam to adhere well. Dunno about the specific brand, but I've used both Boatlife and 3M. The idea that it cracks the paint is a minimal issue, as anything in the seams that squeezes or moves cracks the paint. The thickness of the seam is the main issue here. It sets up and adheres to damp or even submerged wood, in fact uses the water as part of its curing process. It is a good underwater seam compound, and sands and paints well on the topsides--although the flexibility may yield an inferior finish to traditional putties that set up hard.

09-27-2006, 10:17 AM
If the seam maintains its width through the seasons it does not really matter much what you put in there. If the seam moves, the paint will crack no matter what you have in the seam.

In my circumstances where boats are hauled for half the year, I have come to the conclusion that the best seam compound is the one that is most easily removed/renewed. I use linseed oil putty on the topsides and bitumen in the underwater part.

Plywood is a different matter altogether because the seams maintain their dimensions.