Cement Backer Board OK over vinyl flooring?

I am tiling a bathroom over the 4th of July and am considering laying down concrete backerboard over the existing NON-Padded vinyl flooring. The subflooring is 5/8th plywood.

I am not lazy, just thinking that the added water barrier might be a good idea.

I realize it is NOT smart to tile directly onto vinyl flooring. What about leaving the flooring down, applying a layer of backerboard, then tiling?

If I do this, is there anything special I should do -like sanding the vinyl?

Alternately, do you think it would be OK to remove the vinyl flooring and tile right onto the 5/8th inch subflooring? When my wife jumps on the floor I feel only the slightest bounce- no jokes please. It seems the builder intended this approach as the level of the floor tile laid directly on the plywood matches the level of the neighboring hardwood floor just outside the bathroom.

Thanks.

[Edited by RTD on Fri, Jul 3,2009 at 9:26 am EST]

[Edited by RTD on Fri, Jul 3, 2009 at 9:42 am EST]

Remove the vinyl and add 1/2" or better plywood over the 5/8", THEN add 1/4" cementboard or a membrane such as Ditra.

Or, remove the vinyl and do a full mud job, doubt that will happen.

Your ways will be rolling the dice, up to you.

Not that I would do this; but I was wondering if you could go over vinyl if you did a full mud job over it?

Listen to RD- vinyl be gone, and as he said use a membrane such as schluter ditra- a bathroom is a very wet place and an uncoupling membrane such as Ditra is engineered not only for wetness but for overall success in your installation. Removing the vinyl and putting in plywood is not that big of a deal- if you can get the vinyl out in a large piece or 2 you can use it as template for your plywood underlayment. A stitch in time saves 9. cheers. Jon.

Not that I would do this; but I was wondering if you could go over vinyl if you did a full mud job over it?

Nope, shouldn't be done.