I am covering a styrofoam dummy with fondant to make a shopping bag - not very big. Do I need to put buttercream on the dummy for the fondant to adhere?

you can use the tiniest bit, some people just use a bit of water or piping gel, you only need a tiny bit to make the surface tacky

Hi, I use water.

I use a tiny bit of buttercream only if there are marks on my dummies (I've reused them a few times). If the dummy is already smooth, just use water, piping gel, or shortening.

thanks for your help on this! Hoping to get it done today to leave time to dry

Spritz with water, very lightly though. You can also use piping gel or corn syrup.

I always brush with corn syrup.......works like a charm!

Don't mean to hijack your post; but this is related: How do you get the styrofoam dummy smoothed before putting the fondant on? I've seen posts citing both RI and regular spackling paste. Which works better? I tried RI this past week on a styrofoam separator, but it didn't work too well. Perhaps I didn't let the RI harden sufficiently before "sanding" it down? Thanks!

I use crisco on my dummies--no water, no buttercream, no gel.

I find that it fills in the imperfections very nicely and it's easy to move the fondant around, if necessary. I just massage it all over the dummy & cover.

I sand all of my dummies with fine grit sandpaper before doing anything. If big sections are missing or damaged, I get another dummy. Most anything you use will shrink away over time if used to fill a very large hole.

HTH
Rae

Thanks, Rae! I'll give that a try.