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Having owned a VT with a retro fitted concrete floor for two years, I would say steer clear. Concrete is non-porous, the mortar in the walls is very porous, so if there's excessive moisture under the floor it'll come up the walls until it gets above the slab. That said, if he recons the walls are dry it may not be a problem. I have recently found another reason that may behind the moisture under my house being so high, so without that it may be fine.
Understairs cupboards are always musty, might just need a few vents.
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What @Howard & @Silly_Savage said, and why I asked - remedial work would be do dig up the concrete floor. Which can do one.
[Edit] If the plastic is a bodge to fix a damp problem caused by the concrete floor, I'd suggest that resin is a bodge too.
What kind of house is it? Age / Period?
I'd only fix damp stuff if there is an actual problem but if a concrete floor has been retrofitted in to an older property that should have a suspended floor it's worth finding out why and how it was done