Does anyone have any suggestions on how to keep red velvet from bleeding through buttercream frosting?
Sounds like your BC isn't thick enough.
Agree with tiggy2.
I did a four tier square Red velvet cake covered with buttercream and didn't have any bleeding. I use a crusting buttercream and used the crusting buttercream to crumb coat it. Let it set overnight then the next day I covered it with the same crusting buttercream and did the quilted impression mat for decor.
I could be wrong, but are you using a box mix for the red velvet cake? I've heard this complaint a lot with the box mix. (not that there's anything wrong with box mix), its just that it could be part of the problem.
I used the boxix for my wasc red vekvet and have no bleeding. it was a 3 tier wedding cake.