If this is a kitchen and you tile over the existing floor, watch the
height under the dishwasher opening.

It's certainly possible that the older layer might be asbestos tile
and/or have been installed with an asbestos containing mastic.

One red flag for possible asbestos floor tile is a 9"x9" size, another
is an appearance like one of these:

http://mainegov-images.informe.org/d...estosfloor.jpg
http://www.dolir.mo.gov/ls/nursingho...stos_tiles.jpg
http://www.bainenvironmental.com/images/whitetile.jpg
http://www.isitasbestos.com/images/floortile_sm.jpg

Needless to say, you probably don't want to turn a weekend tile project
into a asbestos abatement program, so before removing tile or adhesive
that might contain asbestos have an industrial hygienist or other
qualified individual sample and identify suspect material, and if it is
asbestos research your options, asbestos contaning material can
sometmes be left in place if in good condition.

Michael Thomas
Paragon Home Inspection, LLC
Chicago, IL
mdtATparagoninspectsDOTcom
Eight47-721-0776