Basement drywall ceiling mudded directly to concrete wall

Basement drywall ceiling was mudded directly to concrete wall. I am re-refinishing the space and am lining the walls with XPS foam and 2×4 framing on top. I am worried that the drywall mudd that is on the concrete behind the XPS foam might become a breeding ground for mold. What should be done about the drywall mud on the concrete, should it be removed or dont worry about it?
Replies
I would trim the DW back from the wall so that your XPS can be inserted. Use a long piece of lumber (or something) as a knife guide to keep the cut fairly straight. If you keep it fairly neat, the repair with tape & mud won't be very hard at all.