Laying Travertine Tile

We have a window seat in the living room that is made out of 3/4" plywood and 2x4 framing 16" OC and is painted. We are interested in laying 18x18 in travertine tiles but I have a few questions. 1. Since this is a low impact area mostly used for plants can I use mastic or do I have to use thinset. 2. If I have to go with thinset can I rough up the painted surface or do I need to put down a backerboard? If so I was going to use 1/4" Hardiboard because there will be almost no weight on the tiles. 3. We will be edging the front with 2"x12" travertine moulding. Can I use mastic and hold in place with painter's tape until set?
Thanks in advance for any advice
kb
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Keith Boeheim wrote:

I encourage clients to plan not only for their own use, but for the people who buy the house later. You never know what their kid might do on that window seat. I might not be legally liable for someone getting hurt, but I don't want to be morally responsible either.
It sounds like your seat is plenty strong. I would use the concrete backer board and thinset. Mastic isn't any easier to apply than thinset.
--
Steve Bell
New Life Home Improvement
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