Foam underlayments are common, inexpensive, and easy to install. Using them directly on a concrete subfloor can create problems and damage your flooring instead of protecting it.

The Problem with Foam on Concrete:

Concrete is actually porous, so primarily in basements or slab-on-grade homes, concrete subfloors are prone to moisture wicking up and through the concrete slab. Foam underlay alone does not act as a moisture barrier, and it can trap water underneath your flooring.

This can result in:

• Mold and mildew,
• Warped or damaged flooring,
• Voided warranties from flooring manufacturers

When Should a Foam Underlay be Used?

Foam underlay should be installed over a proper vapor barrier or subfloor system to properly protect against moisture. Some foam underlayments do have plastic backing layer attached, but that may not provide the proper moisture protection needed, and could still trap moisture under the plastic layer.

Avoid Common Mistakes:

Placing foam underlay directly onto bare concrete with no vapor barrier or moisture protection is the leading cause of most flooring failures in basements and slab foundations.

Final Advice:

If you’re installing laminate, engineered wood, or carpet over a concrete subfloor, always, always, always make sure your flooring has the proper foam underlayment and proper moisture and vapor barrier underneath.