neutralizing caustic soda or lye

[Pater]

Does anyone know how to neutralize caustic soda (or lye) that has been used to bleach floorboarding? Some friends in France have a house where it appears that the previous owner (Swedish) may have used caustic soda to bleach floorboards. As a result the floors get wet as it appears that the lye was not cleaned off properly and they absorb moisture from the atmosphere.