I'm sure there's probably already a thread about this.  Everytime I add fondant accents to a custing buttercream, the fondant sweats and becomes sticky. Nothing seems to stop it.  Could it be caused by shortening?

I doubt it's the shortening.  Is the cake cold when you add the accents?  Is it very humid/rainy?  Those are the things that cause condensation [sweating].

If the cake was previously frozen its condensation so you need to let it cool like 2 hours or more before start working again with the cake.

I haven't frozen or chilled the cake.  And seems to only happen when I'm using a crusting buttercream.  I make cupcakes a while back and had put fondant ribbons on them, they began to sweat so much they pretty much 'melted' within about 2 hours of putting them ontop of the icing.  And I made these ribbons about 2 days ahead of time and let them dry to keep their shape.

BUT...I am making my own MMF.  Could that be it maybe? Am I not doing something special to help control the stability of the fondant?

I think it's the fondant more so than the buttercream.  Crusting BC has very little liquid in it--not enough to make anything "melt".

Most commercial fondants have some gums(s) in them that aid in drying--gum paste has more of those gums.  Even commercial products don't really dry rock hard unless you add more gum tex, cmc, tylose, or gum trag. 

Marshmallow fondant, having none of these, probably doesn't develop a resistant crust on it so my guess is that the decos are absorbing grease and any available moisture.

You can add gum(s) to homemade fondant, if you choose.

Maybenot - I'm thinking that may be it.  I'll tweak it a bit and see if I can get a better consistency.  Thanks!!

TL Jones then its the fondant. Fondant should not melt and should not need to be frozen. Never put fondant on the freezer because "condensation" and water is fondant no 1 enemy...trust me!

Thanks. I've never put fondant in the freezer.

You can freeze fondant--or something with fondant on it.  It's the manner in which it's defrosted that matters.

Box the item, wrap the box well in saran wrap & foil, freeze it, defrost the still wrapped box in the fridge, put the defrosted cake [still in the wrapped box] on the counter to come to room temp, and then unwrap & unbox it and it'll be fine.  By doing so, you've controlled the formation of condensation--which is what causes the sweating & the "melting".

Just adding my two sense worth too :) Fondant covered cakes can be frozen...I've done it myself without any problems. As maybenot  says, it's how you store your cake in the freezer and defrost it. I've also actually frozen cakes with fondant on, covered just in plastic wrap and aluminium foil. All the cakes except for two did just fine when defrosted. Two cakes did form some condensation while defrosting but I followed some advice I found on the internet and they turned out fine. Advice was to have the cakes in room temperature and set a fan on them and not touch them until they dried up!! And it worked :) I probably have some help from the climate where I live as well. I live in Sweden and here the climate is quite dry with very little humidity.

Thanks everyone.  I'm not freezing fondant or anything with fondant on it.  I make a cake/cupcakes, ice it, then add fondant accents to it at room temperature - that's what's happening and the fondant is sweating after being on the icing for a while.  I haven't put anything in the fridge or freezer.  This is just all at room temp.  I may try the lmf recipe and see if that gives my fondant a better consistency. I love the MMF but I think mine is just lacking that stability to hold up.