What is your favorite buttercream recipe for crumbcoat and dam on the inside? I've used the buttercream dream and I've also seen the viva method recipe on here as well.

Any recipe can be used for either. The crumbcoat is just thin icing that is spread around the cake. The dam is just thicker icing (can be thicked with powder sugar) that is piped along the inside edge.

I agree with Texas. I use Indydebi's buttercream and I use it to crumbcoat, fill and ice the cake. To make the dam I just thicken with powdered sugar until I can roll it in my hand. I usually don't thin it for the crumbcoat if I even crumbcoat at all.

I read once that a crusting buttercream has to have 4 X the weight of the fat in sugar.
For instance, for 100g of butter, 400g of sugar. The rest of ingredients may vary... But I have seen that 3 X is enough to make it crust.