first off it needs to be noted that vct will conform to any slopes to drains. The slopes should be kept sloping if the drains are still used. If not still used, they can be patched in and over flat and smooth to the surrounding substrate. preparation for vct needs to be perfectly flat and smooth to look right over time. resilient tile will telegraph every substrate imprefection over time. in fact, there is no other floor covering requiring more preparation than a resilient tile floor does. That said, the prep should include grinding and scraping high spots, sweeping and shop-vac clean, filling in the voids and gouges with a cement-based floor patch such as Ardex SD-F Feather-FinishÂ, or Mapei PlanipatchÂ, allow patch to dry completely, sanding and scraping until smooth and flat, sweeping and shop-vac clean again, and repeating this process as necessary so the entire area is smooth and flat with nothing that will telegraph through over time. If you rub your hand over the floor and feel any rigge, high spot, depression, or low spot, it will telegraph through the vct over time. As to ease of install and the tiles sticking, the floor doesnt have to be that immaculately prepped to get the tiles to stick, but if it isnt, while the tiles will stick, the substrate imperfections will telegraph through over time and some deep spots and peaks can cause tile cracking. It all depends what you can live with. We prep to perfection because that is what the consumer demands.

Your foundation and subfloor are the critical aspects. Don't take any shortcuts. Have it inspected by an engineer. I know someone who lived through a nightmare situation similar to yours. Whatever it takes, the subfloor must be perfect and perfectly level. Keep good records and pictures of what they do as they go. The finish flooring is the least of the problem.

If you have cracks, you will need an isolation membrane, for the ceramic tiles, or the tiles will crack. You will need a vapor barrier, over concrete.

In some older applications, a black colored adhesive (called "cutback adhesive") was used to hold vinyl tiles. Both the tiles and the adhesive could contain asbestos. If you have old vinyl tiles or the adhesive residue on your concrete floor is black, you are much better off simply covering it with your new flooring. If that's not possible, hire a flooring specialist properly trained in dealing with asbestos to remove the adhesive. Your family's health is worth the cost.