what problems might I encounter in trying to install ceramic tile  (
cheap from home depot) on an old basement concrete floor, which I
can't see yet, because some owner put in a plywood floor( a little
wobbly now) raised up on 2x3's. The customer wants to know  a price
for the job before beginning, so I can't just tear up the plywood to
see what's under it. The utility room and furnace room have no
plywood, and the concrete there looks reasonable. I've done ceramic
tile over plywood in a small bathroom before. There is one drain waste
vent pipe ( cast Iron)which seems to run along under the stairs

Be professional, tell them you can't commit until you can see the
concrete floor. Alternatively, I would price putting in the concrete
board that you can get from Home Depot I think its 15 bucks a sheet or
something, and go from there.

<q>I've done ceramic tile over plywood in a small bathroom before. </q>

Hopefully not on a floor ?

Don't go there

If it is your first time, and for a client, it will be hell

The plywood is there for a purpose - it is covering major problems

To do the thing properly you need to rip out the lot, test for
unacceptable lumps with a reference point and a straight bit of wood

Then level the area with self leveling cement.
Ceramic tiles (when trodden upon) dislike a moveable foundation.

Better tell the cheapskate to put down cork tiles, his glass will
bounce, and it can be laid on a well pinned down plywood surface.

Of course it is 1960's 'retro' - but that is a selling point.

I am not a reseacher, but am a construction tradesperson.
There is also the potential of serious mold build up (some folks are
very allergic) in the joist bays under the plywood. The prep work
would be very important.  Watch out for revealed cracks once the ply
is removed - potential of water seepage due to wicking caused by
hydostatic pressure on the surroundig watertable.  Seal these cracks
with high PSI patch and sealer.
Sounds like a T&M job rather than a bid.  good luck with it - synapse666b

Hi
 I didn't mean that I put tile right over plywood in the bathroom; I
used the cement board first
Ter