Polyurethane vs. polysulfides?

BALANCE · Post by **BALANCE** » Tue May 13, 2008 7:02 pm

I need to caulk the caprail, it's a Westsail malady due to the hull/deck joint. This is what someone else's looks like with the caprail removed.

I had ordered a case of 3M 101 but just found out that it is on back order. Another WS'er used sikaflex which is a polyurethane.

What's the difference between the two?

Figment · Post by **Figment** » Tue May 13, 2008 9:07 pm

Polyurethane has better adhesion. Polysulfide stays flexible longer, and permits less arduous removal come "one day".

Here's a rough rule of thumb...
Use polyurethane to make a bead of sealant.
Use polysulfide to make a bed of sealant.

(yeah, yeah, polysulfide doesn't play well with some plastics, yellows under UV, etc. We're talking about bedding a wooden caprail.)

Please tell me that Someone Else reinstalled the caprail after that photo!

Post by **Tim** » Wed May 14, 2008 6:06 am

Boatlife LifeCalk (that's how they spell it) is also polysulfide and is a good substitute for 3M 101.

Hirilondë · Post by **Hirilondë** » Wed May 14, 2008 6:12 am

I use Sikaflex 291 LOT on almost everything. If you check the chart Tim posted you will see that it is no where near as adhesive as some polyurethanes. Decide the properties you need from you product, then pick the best one to meet them. Having some adhesion isn't necessarily bad.

BALANCE · Post by **BALANCE** » Wed May 14, 2008 2:35 pm

As always, thanks all for your thoughts. I'm going with the sulfide, it's cheaper and easier to undo (which I think is probably in the cards for the winter).

Fig, yes, the caprail is back on.

Capn_Tom · Post by **Capn_Tom** » Thu May 15, 2008 5:20 pm

I've got the same project lined up for this summer. I've been toying with the idea of using butyl caulk to fill the joint. I'ts a tricky question since removing the caprail is such a big job. I don't want to make the wrong choice. When rebedding the caprail definitely stick with polysulphide. Someday you may need to remove it again and with polyurethane you might end up removing it in pieces.

BALANCE · Post by **BALANCE** » Mon May 19, 2008 8:09 am

Well, I did it and it was THE MOST awful job so far. The prep was the easy part (as it turned out). Contortions are now my specialty. Left hand caulking? No problem. I wish this job on no one. It still baffles me that such a 'well made' boat would have this as an issue. Not removing the cap rail and doing this every couple of years reminds me of that Einstein definition of insanity. It seems though that a permanent solution, lifting the cap rail and applying 5200 or more glass or anything else that has been bandied about is offset with the idea that now you have removed the ability for the hull to flex.....? I'm inexperienced, no doubt, but I just find it so hard to believe that there is not a good, permanent solution.

Rachel · Post by **Rachel** » Mon May 19, 2008 9:41 am

Disregarding that it would be a less-than-fun task, I don't see any problem with permanently bonding the hull and deck together with fiberglass. In fact, I'd consider it a plus. I don't think they need to (or should) "flex" separately.

Rachel

Capn_Tom · Post by **Capn_Tom** » Mon May 19, 2008 6:21 pm

The problem with glassing the joint on a westsail is the hull is only about 3/8 thick at the top which doesn't give enough bonding area. You could of course wrap the edge and bond to the outside of the hull but that is an unpleasant prospect with more grinding and fairing than I am interested in. One possibility would be to build up the gap from the bottom with a turn up the inside of the hull until flush and then lay a single layer over the entire top of the bulwark.