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

By LL Flooring on August 27, 2010

When installing new flooring, you want to protect your investment whether it’s an inexpensive laminate or a top of the line exotic hardwood. 

Moisture is a big concern for flooring. You definitely don’t want it.

We’re NOT just talking about some water spilling or snow being tracked through the house (although, to help with that, we do recommend finding the perfect rugs to use in front of sinks and at home entrances). 

Moisture can come up through your subfloor, especially if you are installing over concrete, or on a level of the home that is below-grade (the level of the ground).

A moisture barrier is needed 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 quieter, significantly more comfortable.

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.
• 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 laminates that already have a pad pre-attached over another underlayment is not typically recommended. Too much padding material can actually lead to a weakening of the joints from the underside resulting in the floor separating. 

Our laminates that have a pad pre-attached have been tested for both sound suppression and support of the locking system and are sufficient. However, for customers wanting extra sound isolation and thermal properties, our cork underlayments are perfect for use under laminates with or without a pre-attached pad. 

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.

Learn about new flooring on our Flooring Basics page.

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In this video below, installation expert Mark talks about the dangers of moisture that naturally rises from concrete, and what that means for new flooring planks if you are trying to acclimate them safely from moisture using 6-mil Poly Sheeting.