Designing Kitchens and Bathrooms - Patching and Filling concrete bed

The concrete bed under the tile in my bathroom has turned out to be in pretty decent shape. There are however, little pittings and crevices here and there, not more than a 1/8" - 1/4" deep. In the far unused corner of the bed the concrete is gone, about 1/2 square foot maybe.

What type of cement patch should I use here? I can use the metal studs in the corner as a sort-of form for filling the missing corner, but I know you can't just have new concrete bonding to old. I read something about epoxy-based fill, but I didn't see it at HD.

Suggestions appreciated.

-Jesse

A self leveling cement works well here. Make sure you caulk EVERY crack crevice around the edges and at the toilet openeing, since the leveling cement will leak out. Just fill to cover the surface and imperfections, anything over 1/4". Thinset will fill in the small problems.

However, if the mortar bed is loose anywhere, it is best to dig it all out and start over with wonderboard or similar.