I am thinking about using a 6 mil poly and a thicker sound/water barrier to make walking on the floors a bit softer. I plan to tape (or use silicon) as a means to seal moisture.

My question is, is it a good strategy to completely seal the floor like this? Judging by my crawlspace (which is sealed with 6mil poly), droplets gather underneath. Wouldn't the same happen for my insulation under the hardwood? Would it damage the concrete?

  • 1
    I would really rethink putting down engineered hardwood in a basement, especially one already with known moisture issues. Also I am assuming the floor is really flat.
    – DMoore
    Feb 5, 2015 at 15:04
  • We are actually going to be putting bamboo which is not per se hardwood. Moisture exists in the crawlspace which is just plain soil underneath. I haven't test the slab for moisture but there is already laminate flooring installed downstairs and it looks like it holds well together.
    – Michael
    Feb 5, 2015 at 15:06
  • If you have "droplets gathering" in the crawl space, you need to increase the crawl space ventilation...either through natural ventilation (more crawl space vents at the perimeter of the house) or through mechanical ventilation (fans and ducts to the crawl space.)
    – Lee Sam
    Mar 17, 2017 at 6:02

2 Answers 2


Use a combined moisture & sound deadening barrier like Roberts Unison 2-in-1. I put this under my engineered bamboo floor. It was an easy install and works great.


You can use a full underlay that includes cushioning as well as moisture barrier. There are also underlay options that will slowly absorb any moisture the concrete sweats and slowly release it in a way that does not harm your floor.

Most floors will need something that has a moisture barrier and cushioning for the warranty to be valid so be sure to have at least those two components.

You can find more information at the BuildDirect learning center link below: https://www.builddirect.com/learning-center/flooring/laminate-flooring-underlayment/

This covers laminate underlay but they will also work for floating engineered hardwood

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