We had the flooring installed in Feb glue down method. Installers had to use levelling compound. After installation our builder covered it in black plastic sheets to protect the flooring whilst other works were ongoing. Water supply has been shut off this entire time. Now that the protective covering has been lifted in April we have discovered black patches of moisture damage in a lot of areas. Flooring company thinks it is because of the black plastic sheets that were used to cover the flooring. They said a breathable material should have been used to protect the flooring but didn't advise prior.
What is the best way to determine the cause of the moisture damage and who should be liable? Does the flooring company have a point or could it have been because the levelling compound was not given sufficient time to dry?