Am doing a wedding cake.8",12" & 16".I know that I have to use dowels & I have a sturdy, silver covered board for the base. Do I have to use thick boards for the other two tiers or do I use the cardboard rounds for the 8" & 12". The cake will be covered in fondant. Do the boards have to be the same size as the cake or slightly larger?
I would use double or triple bords or they will bend and cause you major problems. if you do not want to have to put a border big enough to hide the boards, then you can cut them the same size as the cake.
I use one cardboard (and dowels of course) circle to support each tier. For the 8" cake, I would use an 8" circle. For the 12" cake, I'd use a 12" circle. I would recommend assembly and final borders be done on site. At least that's what I do.
i also only use single boards on layers other than the bottom (with dowels of course)
I have never used more than one board on a tier. Only the bottom board needs to be thick & heavy.