On Mon, 07 Sep 2009 10:27:50 -0500, dpb wrote:

The difference is the level of water resistance; neither is truly
waterproof as epoxy/resorcinal/etc. but use TB-III for exterior work
that does get wet; otherwise no real reason to use it. Well, there is
actually one other reason but not particularly related to the
water-resistance issue; TB-III has quite a lot lower chalk temperature
(I forget the exact number and am too lazy to look it up at the moment
, after all it is Labor Day vbg) but it's roughly 50F. That can be
a benefit in exterior use as well.

TB3 also has a slightly longer open time than TB2 and is less runny than
TB2.

--
Intelligence is an experiment that failed - G. B. Shaw