Should I put a moisture barrier that is rolled on to slab before putting the 6 mil plastic sheeting?

Hello KRBP and thanks for your inquiry. The only requirement for installation over concrete is a 6-mil polyethelyne plastic vapor barrier over the concrete and no need for applying any additional moisture barrier unless you feel that there is a high water table under the home. The Style Selections Luxury Vinyl Plank is 100% waterproof, and the reason for a vapor barrier is basically to prevent mold / mildew from occurring and emitting odors. Hope this helps answer your question. Thanks again for choosing Style Selections Luxury Vinyl Plank.