Tiling over old mastic

[Judithr3]

We want to install ceramic tile on a below grade concrete slab floor that was previously covered with asbestos tile and asbestos mastic. The tile was in extremely bad shape, we assume because of moisture. There were actually powdery holes that went straight through the tiles, and many tiles were loose. A remediation contractor removed the tile by scraping. There is still a layer of asbestos mastic on the slab. We understand that the mastic will continue to loosen from dampness. There is no pooling of water, but the slab does hold moisture. How do we install ceramic tile on this adhesive, which is both toxic and may loosen? Is a liquid separation membrane a good idea? We have also seen solid membranes with raised dots. We have also contemplated removing the mastic residue with a solvent.