Duckman, by "hay," do you mean bundled up dry grass used to feed livestock, or do you mean living grass growing in a field? Since you mentioned making them "stand up," I assume you mean the latter.
The simplest way I've found is to drill little holes in your groundwork, and plant your grass bunches at a time.
I suppose with wet plaster groundwork you could just stick 'em in, but you might not have much time to work with before it dries.
Hope this was some help!
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