: Do you have any feeling for the exposure hazard difference between water
: based LPU and the "oil based" LPU's? I have alwasy had the
: impression that the real nasty stuff in LPU's are isocyanates. But aren't
: they required to form polyurethanes regardless of the solvent?

Quite right. It is the isocyanates that catalyze the formation of the long chain molecules, and even the moisture-cure urethanes have 1.5% or so of isocyanate content. The hazard is less than with convetional two-part urethanes, but the same precautions should be taken, i.e. shop ventilation, skin protection and organic-vapor respirator. Otherwise one could incur a temporary headache and/or skin rash.

The relative percentage of urethane actually contained in "polyurethanes" varies widely. Some are more urethane-modified oils, while others are more oil-modified urethanes. A rough rule of thumb is that the less-expensive ones contain less polyol. The lower the urethane content of the mix, naturally the lower the concentration of isocyanate will be. Regardless of the formulation used, the small quantities and short duration of exposure required to paint a kayak reduce exposure risks to very small numbers.