: Does the moisture curing one part urethane have as high a UV rating as the
: two part?

I asked this of the lady at Noah's and she didn't know but said it was routinely used for boat brightwork.

: Does anyone know if the one part urethane is isocyanate free,it seems like it
: would be and therefore much safer to use?

I'm not sure on this one. I looked on the Sikkens website, but couldn't find the exact product for an MSDS or other technical specs.

: Does it require any special conditions to use it effectively such as low
: humidity to prevent too fast a cure . Does the manufacturer recommend
: roller application or spraying etc?

I have used moisture-cure adhesives at work, where we build automotive interiors. It's the glue we resort to when we have to adhere to vinyl, which has plasticizers that prevent most glues from sticking. It holds extremely well, but is expensive and prone to delivery-equipment problems during the humid summer months (the stuff cures at the application nozzles and can cause the pumps to over-pressure.) Moisture-cure urethanes are also used to glue windshields to car bodies and weatherstripping.

Low humidity isn't a problem. Our adhesives reach full strength within 72 hours -- sooner if it's more humid. I think the only problem with the moisture-cure clearcoat would be working time. If it was really humid, I'd make more frequent trips to the can of clearcoat, only using a little at a time and making sure the can was well sealed in between.

: How many coats are required if you roll it on or spray it?

2 or 3 coats is recommended over previously finished surfaces. The recommend 8 or so for bare wood, but we kayak builders don't need to coat bare wood.

: Even at $100 a boat it would seem that either of these urethane products
: offer much better UV and scratch resistance to any varnish on the market
: and the way it holds up on cars is amazing. Automotive paint jobs used to
: fade badly before the introduction of this technology.