Not all plastic sheeting is waterproof.
Of virgin resin, engineered plastic sheeting is waterproof! HOWEVER Construction and Agricultural grade sheeting (C&A), is not normally considered waterproof.
C&A film (often referred to as visqueen) can have pinholes, fisheyes, and other imperfections, which are considered normal for those grades of sheeting. These imperfections generally keep this grade of plastic sheeting from qualifying as waterproof.
Liner grade sheeting is not supposed to have any pinholes or other significant imperfections, which would allow water to leak from the liner. So liner grade (and all our engineered films) qualify as being waterproof.
Water vapor transmission happens at a microscopic level, where water is a vapor (gas) rather than a liquid. Microscopic levels of vapor transmission do not keep a liner from being waterproof.
What is a good vapor retarder?
The goal of a vapor retarder is to reduce the rate at which water vapor can pass through a the plastic sheeting/liner/ vapor retarder.Putting down any sort of plastic sheeting while waterproof does not stop water vapor from passing through. Understand the perm rating of the liner before you begin your project.
Call 760 597 9298 and we will explain this further.