1. If you have removed plastic tiles and its adhesive is still on the floor, there are special strips that can be purchased to strip it. First use a scrapping tool to remove all of the topical adhesive. Then use the stripper (you can find a list of manufacturers on our website at Cleaners_and Sealers) to remove the embedded residuals of the adhesive. Or you can grind the adhesive off if it is over a concrete slab, but make sure it doesn't have any asbestos in it and provide adequate ventilation.
2. There are some manufacturers of thin-set mortars that say you can use their products to bond to the plastic tile adhesive residuals, but then you are bonding to the adhesive rather than to the concrete slab. You can find a list of tile installation product manufacturers on our website at Installation Products.
3. If the plastic or vinyl tiles are well bonded to the concrete slab there are some thin-set mortars that can be used to bond the tile directly to it, after its surface has been properly cleaned or scarified. You can find a list of tile installation product manufacturers on our website at Installation Products.