Not all Hardwood Flooring Moisture Barriers are Created Equal


Moisture barriers are a crucial component of many hardwood floor installs. Choosing the wrong barrier can result in problems like cupping, crowning, or abnormal gaps in the wood.

At the City Floor Supply one underlayment we recommend is Aquabar “B”. Aquabar “B” is a semi-permeable Class II vapor retarder and it is rated for moderate water-vapor resistance. It is comprised of two layers of kraft paper that surround a layer of asphalt.  This product also meets NWFA accepted product criteria for Class II vapor retarder membrane (0.7 less than or equal to 1.0 perm).

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Unfortunately, in the hardwood floor industry there is a bit of a misconception regarding moisture barriers. Felt and red rosin paper are both often used as moisture barriers when installing hardwood floors. While each of them do have an intended purpose, they are not the best suited products for hardwood floors.

Red rosin in particular actually traps and holds moisture. For example, any moisture that is emitted from a concrete subfloor will actually be trapped in the red rosin product. This will then lead to problems like cupping in the wood floors.

Aquabar “B”, however, is rated for hardwood floor installs. Aquabar “B” has a moisture vapor permeance of less than 1. This slows moisture vapor and allows the wood floor to acclimate to moisture changes slowly and smoothly. Since the product is semi-permeable, it is less likely to trap moisture between the subfloor and the hardwood. Additionally, Aquabar “B” acts as a “slip sheet” to minimize noise and dust.

If you’d like to order Aquabar “B” you can call City Floor Supply at (800) 737-1786 or by clicking here.

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