Scafing Glue

[Nick.K]

Par. Very interesting post, thanks.
When you say "Accelerated cures tend to make the end result more brittle"" are you refering to a polyurethane modified to react faster or one that is persuaded to react faster by adding moisture?
Of the polyurethanes we used, the rapid hardening tube varieties tended to be rubbery rather than brittle...but then I have never studied the failure through a microscope, perhaps time I bought one?

[PAR]

There's more then one way to get polyurethane to dry quicker. Hydroscopic additives can make polyurethanes suck up ambient moisture vapor in the air. I've found these tend to increase elongation, which is what you're seeing too Nick. A good look at the compounds employed is the usual give away as to how they do it, assuming you have a reasonable grip on the basics of these polymers.

In fact Nick, the polyurethanes that are modified this way are the only ones I do like. You can further increase their cure rate, but once they "skin" over this rate drops dramatically and it'll take the usual 2 weeks to get fully cooked. I use these materials as a bedding or light adhesive in many applications, particularly if I need removal later in it's life span. They aren't trustworthy for hard structural joints, as far as I'm concerned, but just fine under a rub strip (as an example).