Building code chunks in rmarkdown/Slidify with io2012 framework

Question

I'm building a presentation using Slidify and the io2012 framework and I can't figure out how to set up the slide so that R code chunks only execute when the slide is advanced(via click or the arrow key). I am preparing a workshop and would like code chunks to remain hidden while I discuss earlier code chunks.

Elsewhere I saw that adding .build to the right of the triple hyphens accomplishes what I would like:

--- .build

OR

--- {.build}

But neither works for me.