Hi all
I am going to be making some letters to stand on a cake, I however only have alittle bit of Gumpaste and am not going into to town for a couple days, How much Gumpaste powder do you think I need to mix with Fondant so that it hardens well enough to stand on my cake without crumbling?

Even just a little gumpaste in the fondant should dry hard enough to stand up. Ive even used straight fondant if it has a good 3-4 days drying time and it isnt too thick! HTH

If you have plenty of time for them to dry, fondant alone works fine. I've never used gum paste powder...just pre-made gum paste to mix with the fondant or tylose...I'm assuming you wouldn't need a whole lot especially if you do have some drying time.