I want to use isomalt to make a moat around my castle cake. I'm thinking of layering foamboard to form a cavity around the castle to hold the isomalt. Will the isomalt melt the foamboard? I also thought about using fondant or gumpaste "rocks" to cover the edges and/or bottom of the moat. Any suggestions ?

i would make it on a surface that can handle the heat and move it to the board -- you could use aluminum foil to pour it on and move the whole thing -- I'm guessing that florist foil would melt but I'm not sure but blue foil would be cool under there --

you can buy chocolate rocks that are delicious -- you could snack on those while you make the others out of fondant hahahaha

if you just got a bunch of blue hard candy -- you could just melt that on foil in the oven -- 

Thanks K8memphis. I will have to play around with this. I do have Isomalt already. Have you ever tried it the way you suggested?

on foil yes in cooked sugar, isomalt, venuance pearls and melted candy 

but pouring onto  a silicone mat would be a good choice too -- but you need to place something to act as a bumper or be ready to flip it over onto itself as it cools & stops spreading to form it into your shape

i find it interesting that you would challenge my experience -- I could take pictures of my equipment -- I could direct you to ices in Illinois some years ago where I made a blown sugar model in front of an audience -- 

do you disagree with my advice? why do you find it questionable -- not enough pictures in my gallery perhaps?

i think you'll have a real problem pouring it onto a foam board but I haven't done that -- it might work but I would not try it myself -- 

one way you could do it would be to first pour it out on silicone-- then start flipping it over and over and kneading and pulling it and it will cool and you could lay it in there probably/maybe after that -- it's incredibly easy to get horribly burned -- and you seem new at this so I just imagined pouring it from the pot -- clearly that won't work --

there's a big learning curve here for skill and safety -- you probably already have but be sure to check out some you tubes on this --

best to you

pulling it will make it cloudy if you want that effect

No offense intended.  Thanks for your advice. 

no of course not -- none was taken -- why did you ask though -- was my first answer too glib?

please let me know how you do -- best to you

Thanks.  I'm going to try the foil lining.  I'll post a pic. This is for a cake show in October so I have a while to play around.