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All About Underlayments: Purpose, Benefits & Install Tips

by Crystal Hosking - Hosking Hardwood Flooring, Inc. ©2013, Copyright Protected. All Rights Reserved

Underlayments play an important role during the installation of new hardwood flooring or laminate flooring. Whether you intend to staple down, nail down or float, an underlayment offers a slew of benefits during and after installation.

Staple or Nail Down Installation

With a staple down or nail down installation over a wood subfloor using solid flooring or engineered flooring, it is recommended that an underlayment of 15lb. black felt paper is rolled out over the wood subfloor prior to installing the new floor. This hardwood felt paper is necessary to greatly reduce the chance of any moisture coming up through the subfloor and will help protect the new hardwood flooring. Even if you think you don't need it and you're tempted not to use it, it's always better to be safe than sorry. Especially when being sorry could mean $1000's in damage. 15 lb. black felt paper is relatively inexpensive and can be the difference between warped hardwood flooring boards in the future or a floor that stays perfectly beautiful for a lifetime.

15lb. black felt paper for flooring installations over wood subfloors looks a lot like roofing paper, but it is very different. Roofing paper is typically coated with asphalt or tar, which will emit harsh chemical odors, especially if enclosed in your home. Therefore, it's important to make sure the 15lb. black felt paper you're using is manufactured specifically for hardwood flooring installations.

Installation of 15lb. black felt paper is incredibly easy and fast. Simply roll the black felt paper out over the plywood subfloor, overlapping the seams approximately 4 to 6 IN. and then use a hand stapler to attach to the subfloor.

Floating Installation

Underlayments pads are especially important for engineered floors or laminate floors which are installed via the floating method over wood or concrete subfloors. When you float an engineered or laminate floor, none of the boards are actually attached to the subfloor. An underlayment is necessary for multiple reasons, floating floors will expand and contract, moving ever so slightly as a whole unit. The smooth surface of the underlayment allows the flooring on top of it to move slightly during seasonal relative humidty changes. Underlayments are also are used under floating floors to act as a cushion, allowing for a bit of a softer feel when walked upon.

 

 

Some underlayments pads these days are made with an attached plastic moisture retarder. 4-6 mil Plastic moisture retarders are basically non-negotiable when it comes to installing over concrete subfloors, we always recommend the use of a moisture retarder over concrete subfloors. (For underlayments without a moisture barrier attached, you can always install a 6mil plastic sheet separately directly over the concrete slab.)

Underlayment pads also helps to even out subfloors which may have minor imperfections, which is important for a smooth floating installation process.

Lastly, some underlayments pads have exceptional sound absorption properties and can be used as a sort of sound insulator, preventing sound transfer.

There are a multitude of underlayments available for floating installations. They range from simple foam pads to foam pads with a plastic moisture retarders attached to dense felt-like underlayments with remarkable sound absorption properties. Foam pads are typically thinner and their sole purpose is to add a little cushion. Foam pads with moisture barriers attached are also on the thinner side but also offer that moisture protection. The denser underlayment pads (usually a felt like material) are typically a bit thicker and offer more support and insulation because of there dense nature. Please note... that "Regular Carpet padding" is too thick and soft to use as an underlayment pad for any wood or laminate flooring and could cause the joints of the flooring to break when walked on.  

Some hardwood and laminate manufacturers make their own underlayments for floating applications, which they recommend for use with their products. However, in most cases, any industry approved underlayment will get the job done. It's important, prior to installation, to read the specific flooring manufacturer's installation instructions. If they require use of their brand specific underlayment in order for their warranty to be effective, it's always a good idea to acquiesce. 

Installation of underlayment for a floating floor is very simple. Underlayments typically come in rolls. After subfloor prep, simply roll out the underlayment. Many underlayments these days have self-stick overlap flaps for connecting multiple sections of underlayment together. If the underlayment you are using doesn't have these, you can simply use duct tape to secure the edge of one portion of underlayment to the other. (Some flooring manufacturers will sell seam tape, but, really, duct tape works just as well.)

 

One of our top selling underlayments (shown above) is Silent Stride underlayment pad is a dense felt-like material, using air-laid filaments. This product is renowned in the hardwood flooring industry as being one of the most advantageous underlayments for floating floors. Features of Silent Stride Underlayment include: sound absorption, moisture protection, minimizing of subfloor imperfections, insulation and anti-microbial properties. On top of all that, Silent Stride is pretty affordable when compared to similar products in its category (cork or rubber underlayments, which share some of the same properties). 

 

Cork Underlayment

Cork underlayments are certainly gaining popularity over synthetic underlayments in both residential and commercial settings. But, what are the major benefits of using a cork underlayment? Cork is a natural product from a renewable source. If you're looking to go more "green" with your home, cork underlayment is a step in the right direction. Cork underlayment also has superior sound deadening qualities more than most any other synthetic underlayments previously mentioned it also helps minimizing subfloor imperfections, adds a degree of insulation and has anti-microbial properties. Many homeowners with allergies love cork as it is naturally anti-bacterial as well as anti-fungal. It's important to remember that cork is naturally water resistant, but not waterproof. Therefore, a 6mil plastic moisture retarder is recommended under the cork for installations over concrete slabs.

Cork underlayments can come in a variety of thicknesses. We've found that the most popular are the 1/8 IN. thick cork underlayment (3mm) and the 1/4 IN. thick cork underlayment (6mm). The only difference is the thickness, the thicker 6 mm will give you twice the sound absorption if desired to lessen any noise when the floor is walked on. Cork underlayments can come in either rolls or sheets. If an installer needs to add height to a subfloor, he'll often choose to use the thicker 1/4 IN. cork underlayment, as most synthetic underlayments measure up at about 1/8 IN. thick.

Cork underlayments are a bit different from other underlayments, because they can be used in staple/nail down installations, floating installations and even in glue down installations. If you plan on installing your flooring via a staple or nail down method with a cork underlyament, you can choose to either float the cork or tack it down to the plywood subfloor. For floating installs, you can either float the cork underlayment or you can tack it down to the subfloor; and then simply install the floating floor on top. If you choose to glue down your engineered hardwood flooring using a cork underlayment underneath you would need to glue the cork down securely to the subfloor and then you can glue the hardwood directly on top of that cork.

Laminate Flooring with Underlayment Attached

Some manufacturers, like QuickStep and Alloc, make laminate flooring with an underlayment already attached to the back of each board. This makes installation quick and simple, negating the need to roll out a separate underlayment. Just keep in mind that if this attached underlayment does not have a moisture barrier attached as well, it's always a good idea to lay one down prior to installing your new laminate floor.

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Overall Rating: 4.5 stars - 99 reviews

By:
Date: August 5, 2020
Page Rating: (4.5/5)
Comments:
Hi guys, I like the article and detail. Im looking to not remove my 40year old solid oak 9"parquet 3/8" thick that is black adhiesive glued down on slab. My wife would just like a different wood floor. We did pergo in our cabin over foam and is too clickedity clack loud. She selected a 3/8" hardwood that is hickory birch, 4", 7" wide. My plan is to 40grit sand and float with a fixall the only 20ft sq area that is 1/8" low. Then install 30lb flooring felt. The new floor has 1/8" bull nose, TandG and doesnt click/snap together. Must I 45 degree nail it down, (I dont think the oak will like it and slab is underneath). or instead use a 1/8" tooth trowel with adhesive. Floating it is my preference but it is a non snap floor. Would this be a bad choice and I must get snap together? Im fine with replacing the base and trimming doors. The only other thing is my kitchen is linoulem over slab. Im planning to use a liquid self leveler to get to the existing oak floor height then follow
By:
Date: August 1, 2020
Page Rating: (5.0/5)
Comments:
I was not aware of cork as an underlayment. After reading this article I will be using cork.
By:
Date: June 25, 2020
Page Rating: (5.0/5)
Comments:
Very informative
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Date: April 9, 2020
Page Rating: (4.5/5)
Comments:
I am pricing out a job that involves engineered flooring installed on top of quicktrack radiant heat over 3/4" advantech subfloor. there is a crawl space underneath. new construction with a good waterproofing system on foundation but no guarantee of not having any moisture present at one time or another. with radiant tubing, what underlayment do you suggest that could perform as some level of vapor barrier but not interfere or react with heat from tubing. do not want a smell issue or a problem with reflecting heat back like a foil face might. I also thought about doing closed cell spray foam under subfloor as a vapor barrier. thoughts?
Reply by HoskingHardwood : We usually prefer using a floating engineered floor system when it comes to flooring for radiant heat,with that we use Silent Stride underlayment Or Cork underlayment which can be used under nail down installations. As far as a moisture retarder we use several coats of Shellac applied to the subfloor first which provide great vapor retarder seal but still allows the heat to transfer.
By:
Date: February 11, 2020
Page Rating: (2.5/5)
Comments:
if installing cork underlayment over concrete, with 6 mil plastic, how do you accomplish glue down installation per this article recommendation?
Reply by HoskingHardwood :  The method you describe would be when using a floating floor system.  If you want to use a glue down installation method over concrete you would want to first use an adhesive that has a moisture block within it like a Bostic Product directly over the concrete. Optional use of cork is fine but would also have to be glued over the slab adhesive then the flooring glued down over the top of the cork. 
By:
Date: February 10, 2020
Page Rating: (5.0/5)
Comments:
It was very reassuring to read this article to be sure that the installation is done correctly. Thank you so much!
By:
Date: November 30, 2019
Page Rating: (5.0/5)
Comments:
I have a concrete slab floor with hydronic heating in the slab I would like to install engineered wood flooring over What type underlayment is best Thanks
Reply by HoskingHardwood : We would recommend using Silent Stride 
By:
Date: November 8, 2019
Page Rating: (5.0/5)
Comments:
Thank you for the valuable information on underlayments. In regards to cork, I understand the need for extra moisture protection over a concrete slab, but what about on the second floor over plywood subfloor, is the cork enough? Thank you
Reply by HoskingHardwood : We wouldn't recommend using "plastic" vapor retarder on wood framing. Cork would be fine to use over the plywood.
By:
Date: October 20, 2019
Page Rating: (5.0/5)
Comments:
In a floating hardwood installation on concrete, can I lay poly, then 1/4"cork AND 1/8" Dura-son on top...to get better acoustic control? Cork has a high compression value...its stiff. Dura-son is cumbled rubber. Helps with height too..3/8"
Reply by HoskingHardwood : Probably could. 
By:
Date: October 13, 2019
Page Rating: (5.0/5)
Comments:
I have plank subfloor (older home) and recently removed the previous hardwood flooring. I am reinforcing the subfloor with 2 1/2" deck screws and then screwing down plywood on top of the plank subfloor. Between the plank subfloor and plywood do I need to use an underlayment paper/material to protect against moisture or only on top of the plywood between finishing surface?
Reply by HoskingHardwood : I would suggest putting the "Black Felt paper" over the top of the subfloor (under the hardwood) 

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