Question for the Chemist, or somebody...

[Dan McCosh]

I was sealing a seam on a metal roof with something called DeWitts rubber sealant--which is supposed to be a neoprene compound. It's interesting stuff, having some of the qualities of asphalt roofing sealant. Dries kind of stretchy and rubberlike, softer than polysulphide. I, of course, started thinking about seam compounds, having used roofing sealants successfully in the past. Question is: what is the stuff? (It's supposed to last 20 years or so, and seems to have possibilities.)

[thechemist]

I dunno whatzis. If it is supposed to be some sort of neoprene compound , well, it might be........depending on where the supposition come from.

Adhesion........again I dunno except to warn that things that sitck to old, oxidized galvanized steel roofs don't always stick underwater to wood.

Take some and put it on a piece of wood and tie a fishing weight to it and a bit of baling wire and hang it in the water for six months, and then come back and tell me what it did and we will both know.

Wish I could have been more help, but I am not familiar with the stuff.

[Bayboat]

It seems like a lot of people are looking for substitutes for seam compound. I wonder why, when there are several good tried and true marine compounds on the market, for example Interlux and Sika.

[Dan McCosh]

It's a good question, and the answer is that the perfect seam compound is as elusive as the perfect varnish. Traditional oil-based seam compounds are pretty good, although I can't really use a knife-grade compound, due to the time and effort it consumes in the 1,200 feet of so of seams I have to deal with. The main problem is the paper-clogging that comes with oil-based compound when the bottom is being sanded. The Sika products are urethanes, which I avoid for the usual reasons--mainly the difficulty of dealing with old compound, and poor adhesion in old seams. Polyhsulfides work pretty well, are easy to sand, but likewise don't adhere to old compound very well. So it goes.

[Bob Adams]

It's a shame, because I haven't seen it in years, was some imported stuff called Seal Once.This was a polycarbonate based goo, dispensed from a tube which when cured had the feel of chewing gum. When removed from a seam after years of submersion, it would still adhere to itself and to wood. Was great stuff, naturally you can't get it anymore.

[Bayboat]

Bob: Yep, that was good stuff. Another good seam compound was Kuhl's, which I haven't seen for years.