Moisture Barrier and Underlayments: Don’t Leave It Out!

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When installing hardwood floors, you want to protect your investment whether it’s a $0.69 laminate or a $6.69 exotic hardwood.  Moisture is a big concern for flooring, you definitely don’t want it!  And we’re not just talking about some water spilling or snow being tracked through the house (although, to help with that, we do recommend putting down rugs at home entrances and in front of sinks).  Moisture can come up through your subfloor, especially if you are installing over concrete or below-grade.  A moisture barrier is need to protect the flooring against moisture or moisture vapor.  Along with the moisture barrier, you may want to install an underlayment.  It insulates and cushions the flooring, making it more comfortable to walk on. 

For moisture barriers, there are three basic methods of protection:

  • Nail Down Installations – In crawl spaces under the subfloor, 6 mil poly sheeting plastic should be placed over the dirt.  IN addition, a 15 lb felt paper should be placed between the sub-floor and the new hardwood flooring.
  • Glue Down Installations – When gluing down wood to concrete, a moisture barrier is almost always needed, especially below-grade.  Usually, a trowel applied product is recommended, such as Bostiks MVP or Mapei’s WFM.
  • Floating Floor Installations – When installing laminate or other floating floors over cement, VCT, ceramic tiles, or kitchen vinyl, use 6 mil poly sheeting plastic as the moisture barrier.  Omit plastic when covering bare wood subfloors thereby allowing the subfloor to breathe.

Some underlayments have a built in moisture barrier.  These are typically used for floating floor applications.  If you live in a condo, many have association rules regarding noise levels.  Underlayments can really help absorb sound.  As well, they can insulate the floor, leaving it warmer in the winter and cooler in the summer.  Cork is especially popular for these types of applications. 

One thing to consider when choosing an underlayment is that in this case, too much can be a bad thing.  Installing laminate that already have a pad pre-attached over another underlayment is not recommended.  Too much padding material can actually lead to a weakening of the joints from the underside resulting in the floor seperating.  Our laminate that have a pad pre-attached have been tested for both sound suppression and support of the locking system and are sufficient.  However, for customer wanting extra sound isolation and thermo properties, our cork underlayments are perfect for use under laminates with or without a pre-attached pad.  The Quiet Walk (which has a built in moisture barrier) and Insulayment underlayment would also be appropriate.

Both moisture barriers and underlayments are important parts of your floor.  Make sure you find out what works best with your needs to have the best experience you can with your beautiful new floors!

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23 Comments

  1. I am rebuilding my basement floor after a flood with a sub-floor with 2×3’s ( floor is too uneven to install laminate directly on concrete) and since no vapour barrier was put under the concrete, I want to know if putting a 6mil plastic vapour barrier directly on the concrete will do any harm. I will be installing 1 1/2 foam bettween layed down 2×3’s, laminate underlayment, and then 12 mm laminate floor.

  2. MICHELLE M HARE on

    I plan to install coreluxe ultra EVP over a concrete basement floor. When I installed a lesser level evp over a wood subfloor on upper level I was advised to buy this peach this foam like under layer which seemed to aid in keeping it in place. With the coreluxe ultra would that already have an underpad and not need the foam roll? And would the floor slide around or shift on the 6 mm plastic and come apart. My upper floor seams split right in the center after i put heavy furniture back, hoping to avoid that this time, also was given completely different advise from multiple associates on what to buy for under my floors so I wanted to see what a query from this site yielded.

  3. Question, we have put down a vinyl wooden tiles and used the 6mil moisture barrier underneath it. We have begun to notice that when you walk on the floor you can hear the moisture barrier underneath it. How can we omit this noise? The moisture barrier is covering cement/concrete.

    • Lumber Liquidators on

      Thanks for your interest, Ann! Yes, a moisture barrier should be used when floating over concrete.

    • yes, try covering every room with a moisture barrier. I did, but didn’t in my kitchen with a linoleum floor and now may have to take it up and put in some barrier as I am having trouble with condensation leakage.

  4. My son’s laminate floor has water damage from a washing machine could it be dried out with a humidifier or hot iron with towel?

    • Lumber Liquidators on

      Thanks for your question! A hot iron w/ towel should not be used – that could damage the finish on the floor. A humidifier and/or fans may help the boards dry and straighten out. Please reach out to our Tech & Installation team at 800-366-4204 for more tips and best practices.

  5. When installing Hermitage Red Oak (Quick Click) as a floating floor, it is recommended to use 6 or 8-mil vapor barrier with an impermeable vapor barrier to limit moisture. Thanks for asking! – Lumber Liquidators

  6. just purchased the Hermitage Red Oak Quick Click Floor. I plan to install below grade (basement) on top of concrete. also I purchase the ECO Silent Sound HD Underlayment for moisture barrier. Do I also need the 6 Mil Poly Sheeting?

  7. I intend to install laminate flooring. I live in second floor condo with cement floors with hot water heating pipes in the floor. Do I still have to install a vapour barrier first?

  8. Hi I’m confused. I live in a condo 2nd floor, my floors are concrete and I’m planning to install laminate 12mm, I got the underlayment 3 in 1 its 4mm. Do I still need to use the moisture barrier plastic or with the underlayment will be enough?

  9. I am putting a pre finished hardwood (Hickory) floor down over a plywood subfloor that is over a crawlspace od aboyt 18 inches. Which moisture barrier would you reccomend?

  10. So if I have a laminate with no pad attached and am installing in the basement over prior vinyl flooring, and I have Eco Silent Sound, is that all I need or do I need another pad for cushioning? Also, if I choose instead to use a laminate with a pad attached, should I not use the Eco Silent Sound and instead use only a moisture barrier?

  11. I am installing a 10mm laminate with a 2mm pad attached on a wooden sub floor (press board) in a family room. The room is over a crawl space. I was told I needed to put down a moisture barrier, but I am seeing different opinions. I have the sub floor prepared and ready for install. Where do I go from here ?

  12. Hi Aaron, Depending on the underlayment you choose, you may or may not need one. These are the approved underlayments for gluing down Morning Star Bamboo over concrete: Bellawood Premium, install (film side up) Eco Silent Sound install (film side down) Dream Home Insulayment, install (smooth side up) Dream Home Cork (3/8″?thickness). Requires plastic poly-sheeting when placed over cement. Requires PVA wood glue be applied to the short ends. Installation instructions for all should be available in our Flooring 101 section. I hope this helps! Our Tech & Install team can provide additional assistance at 800-366-4204.

  13. Hi Tom, You should never install a laminate floor or another wood flooring product over a wood subfloor that is installed over concrete in a basement unless you are certain that the wood subfloor has a vapor barrier underneath of it that has a perm rating of .15 or less. If there is no moisture barrier under the wood subfloor, our Tech & Installation team suggests removing the wood subfloor and installing the laminate floor over the concrete using 6 mil polyethylene sheeting under the laminate. You could also keep the subfloor and install a vinyl click product over it. We do offer underlayment pads like Bellawood Premium underlayment that will block 6 lbs of concrete moisture. This pad can be installed over wood subfloors, and can be installed under laminate floors. Keep in mind the pads have limitations on how much moisture it will block. For further assistance, you could try contacting the Tech & Install pros at 800-366-4204. I hope this helps!

  14. I’d like to know what the answer to Mikes question was, because I have the same experience. I was told just to use the Bellawood premium underlayment. After watching a video it said I still need moisture barrier and on the website to not use extra padding…lots of conflicting information.

  15. Hi Mike, thanks for your question. Please contact our Tech & Install team at 800-366-4204 for detailed assistance!

  16. Good morning, and thanks for your question! The additional padding is not required, however the recommended products to use for the Golden Teak Laminate are: Underlayment: Eco Silent Sound HD, Dream Home Insulayment, OR Bellawood Premium Underlayment and Moisture barrier: Dream Home 6 mil Poly Sheeting over concrete I hope this helps!

  17. I bought the golden teak laminate at lumber liquidators and the salesman put me down for a underlayment from nirvana plus which is a sound and moisture resistant. My question is will that be too much padding since I already have padding on the underside of the laminate? Also is the underlayment good enough to keep moisture from the concrete from seeping into the flooring or do I need a vapor barrier as well?

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