I am going to install ceramic tile on a floor
which has black tile mastic appx 40 years old
how should I prepare the floor and what type
of adhesive should I use?

I failed to mention in my original message
that the existing floor is concrete.

thanks
Bob

[This message has been edited by stamper (edited August 15, 2000).]

 

This is the opinion of an DIYer. I welcome any professional to correct me.

(1) Clean the subfloor, level, smooth, and with no flex.
(2) Buy cement board (Wonderboard, Hardibacker, Durock). Use 1/2" or 1/4", depending on how high you want the finished floor. Cut it to fit.
(3) Trowel down (use 3/8" by 1/4" square notched trowel) a polymer enhanced thinset mortar (Versabond is one brand).
(4) Set the cement board into the mortar and screw (special screws for this purpose) or nail (roofing nails) it down. Leave 1/8" expansion gaps around the permiter and between sheets.
(5) After waiting a day, use the same mortar and trowel to set your tile.

 

The adhesive you describe, also known as cutback, is a problem. As thin set will not stick to it. It may look good at first. But will not hold to it for long.

1 It can be ground off. But most contain Asbestos. So this is not recomended.

2 Use of a Slip Sheet. This is a thin material (same as what's used on the back of sheet vinyl).. This is attached to the floor using vinyl floor adheasive. Then the tile is layed over this.

3. I recently heard, of a new thin set additive,(not sure of the name) that allows thin set to bond to this. I have not tried this yet, but plan to try it soon.