What combo to use for Earth shiled cocoon?

So I've been playing magicka for the past few days. I'm new obviously and I'm still getting the hang of somethings.

I was in the area where you fight jormungandr or how ever you spell it and I had cast earth + shield on myself to get the shards of rock to come out and make a cocoon around me, which would disapear on cast of a new spell. Now when i go to self cast this same combo I get spikes coming out of my body. Same deal with Ice and Shield combo.

Am I doing something wrong? Or is there another way to get the cocoon thing?