I do not think you need backerboard. I had a similar situation. Just prime the wood subfloor and pour SLC and tile over that. Our contractor was going to install a plastic mesh imbeded in the SLC, but it appears that is not necessary either.

Here is a link that might be useful: Other Post

Well, I guess my work here is done! :-)

Thank you both for your help.

One more question. We are NOT installing any wires for heating elements. The floor is for a small bathroom 8 x 10 (including tub).

Do we need to install wire mesh/wire for proper strengh with the SLC?

Or just the following:
sub floor(s)
SLC Primer
SLC
Tile.

Thanks again. We are very handy DIY's with a 100 year old house, but a tile floor was new for us.

Amy

There was a statement from the pros on the link:

"There is an "open time" or working time with the SLC primer, so once I spray on the second coat, I have a certain amount of time to get the SLC mixed and set down over it."

What does this mean...once the wood is primed, you need to get the SLC in a certain period of time. So I can prime and come back at a later date to pour?

Forgot to add...wouldn't the plastic mesh be better than no plastic mesh. From what I read, you lay the mesh down and pour over it. I would think it would help bind everything together. I read this post and was interested in this being I am doing the electric mat install too.

Most SLC's I've worked with, the primers require that you wait 2-3 hours for it to dry, and then pour within 8 hours or you'll have to reprime.

Forgot to add...wouldn't the plastic mesh be better than no plastic mesh.

The problem being that it creates weak points between the sheets of plastic mesh. The whole idea of using any kind of lath-- plastic or wire-- scares the bejesus outa me because there've been so many failures as a reult of it.