We are remodeling our basement bathroom because it was leaking into our guest bedroom. when we gutted it, we found out the plastic shower had a gap between the pan & drain. consequentely there was mold everywhere, along with wood debris in the drain! There was no connection between the shower drain and floor drain. Can i seal the concrete and use the floor drain as a shower drain? I have seen this arrangement in school basements.

what you see in a school locker room is a floor drain
what you dont see, is the drain pan material connected to the floor drain. so that the water wont seep into the foundation. there is no way to water proof the connection floor to floor drain, unless you install poly/shower pan material,
that intails, busting the concrete, putting in the material, and pouring back the crete.
others may tell you to spray epoxy paint over the floor and walls, but that wont stop the water from seeping around the drain
sorry...frodo

you will first have to get to the drain line, ensure there is a trap, and then decide on which direction you will go from there. this means you have to get down to the basement slab, and bust a chunk out around the existing drain.

if you are going to use a Schluter kit, you then follow directions in the kit to build up the floor drain. you will have to cut off the existing grate assembly, possibly lengthen the drain line vertically, and use their material from then on.

if you are going to make a mud pan from mortar, drain liner, sand mix cement, and a drain end and grate, you need to check websites for those materials. check oatey and sioux chief, for instance. the drain liner has got to come up the wall, and over the curb, to contain the water within the drain field of the drain grate assembly.

I have recently seen a collar and plastic arms that make smoothing the correct slope into a mud pan much easier, wish I'd known of it when I built ours a year ago in the basement.

don't forget to account for the thickness of your tile and thinset when you calculate your dimensions, cut off the drain pipe, and mount the drain/grate assembly, or you will be one sorry dude.

swschrad is correct for a shower stall,
i think that you are asking about a gang shower with no stall, just a floor drain in the room,
for that you will need to bust the floor, and install a 3ft x 3 ft poly shower pan material
under the crete and attached to the F.D.
that will suffice for any seepage that will occur around the F.D.
water seepage will ruin your foundation, the water will wash the dirt away leaving a void under the house.
post back with more info
frodo

hoping to avoid busting floor. sounds like this only option. could i install a tub and run the drain to the floor drain and extend it into the hole? the existing floor drain drains fine.

you can....but...it will be a splashy sob
cut a hole, the size of your drain in the floor drain grate, run the pipe over to it, and put an elbow on the end of pipe, looking into the FD
that will hold down some splash. but not all
also. a tub drain. drains out the bottom of the tub
so you will either have to raise the tub up on a platform OR order a raised "apron" tub
they come in cast iron, not baked enamel or plastic
pricey...
after setting your tub
use 1 5/8in unistrut bolted to floor to ancher pipe
also use 7/8 in unistrut. bolted to floor
he diff heights will give your pipe "fall" twards FD
use a unistrut pipe clamp to attach pipe to unistrut
ask at a plumbing supply for these items
homley bebo does not carry it
tell salesmen what your doing,to get correct size clamps.
ie.1 1/2 pvc use 1 7/8 clamp.. size matters!