Masonry will use the "Excerpt" text that can be defined in the post editor; if you're not seeing the editor box for excerpt, you may need to enable it in the "Screen Options" dropdown (top right corner of the editor screen).
I mean, how can I control how many number of words will be displayed from the excerpt field?
Is there a way?.. or it does not make sense at all?... I would just instruct my editors to limit it...