Hi, I am wondering if it is a good idea to put a subflloor over the basement concrete under the shower base or if I should just use mortar or even PL200 glue.

Are you using a pre-built shower base?

If so, then I would NOT put down a subfloor. Unless it was a cementatious type. (Hardi, DuRock, etc). Even then, as long as the floor was level, clean and relatively free of cracks, I would probably still not put down a subfloor.

Depending on the manufacturer of the sub-base, they may require that it be laid in a mortar bed.

These are just my thoughts. I would suggest to wait to see what Tom (Speedball1) has to say.

Dan

Please post plumbing questions on the plumbing page.
Thank you, Tom