Flexbond and Versabond are both modified thinsets.

You can get the same by using dryset, which is the unmodified CustomBlend (or MasterBlend), and adding the liquid acrylic latex modifier in place of some or all of the water.

In your situation, concrete trim over stucco, you'll want the best bond you can get.

"Best" means that the bond will not only be strong, but can withstand and difference in the rate of expansion between the trim pieces and the wall that they are bonded to.

You get that "flex" in the bond joint with the addition of the acrylic latex modifier.

In your situation, between FB and VB, I would have chosen Flexbond. Simply because it's more modified than Versabond.

Since the installation instructions say "modified" and you're using "modified" you can continue with your existing materials.

You can certainly continue with the Versabond as is since you've already purchased it. If you want to "juice it up" a bit more, you can get a jug of the acrylic latex additive and add some when you mix it up.

With an exterior situation like yours you want a strong bond, and unless the installation instructions differ, you probably want to make sure that you have full thinset coverage between the trim pieces and the stucco.

You don't want and cavities or voids where water could enter, freeze, and cause the trim pieces to crack, spall, or come loose.

Best, Mongo

Normally I would "laugh" at the water freezing comment since I live in Phoenix. But this year, we had many areas of the city where pipes actually burst from freezing. Whodathunkit!

Anyway, the first piece is coated very well and is stuck solid. We made sure of that. But I have other things I can use the Versabond for and it's cheap enough that I think I'll go ahead and switch to the Flexbond. Thanks again for your wonderful advice.

I used to live in Tucson back in the late 80's early 90s.

My in-laws came out to visit, my father-in-law hoping to golf. They'd come out for a week around Jan-Feb, looking for a break from the Wisconsin winters where they lived.

Each and every time they came out it snowed!

Best, Mongo

Yes, people are surprised that we get snow in the desert. I live far enough north so we can usually go about 15 minutes farther north to play in the snow.