Laminate

Underlayment for Floating Floors

When a floating floor needs separate underlayment, when it doesn't, the 6-mil poly question over concrete, and thickness limits, by manufacturer.

Updated · 3 min read

Underlayment rules depend on the product. Attached-pad floors usually take nothing extra, laminate without pad needs a foam underlayment, and over concrete most makers want a 6-mil poly vapor barrier. Mannington is the exception. Follow the sheet in the carton.

Attached pad: add more or not?

Manufacturers disagree on adding a second pad.

Product Extra underlayment under attached pad
Pergo Extreme No separate underlayment allowed[2]
Mannington ADURA Max Additional pad not recommended[4]
Shaw (COREtec, Floorte) A second underlayment is allowed in residential use, no more than 3 mm thick[3]

Shaw's sound testing doesn't show any added acoustic benefit from a second underlayment, and crumb rubber underlayments aren't acceptable under its resilient floors.[3]

Laminate without attached pad

Laminate needs an underlayment under it, but only one layer.

  • Use foam underlayment when the product has no attached pad, and never install Pergo over more than one layer of acoustic underlayment.[1]
  • Laminate pad can't be thicker than 3 mm.[5]
  • Underlayment supports the locking system, adds moisture protection and evens out minor subfloor flaws.[7]

Over concrete: 6-mil poly

Here Mannington parts ways with the others.

  • Pergo laminate requires a 6-mil polyethylene vapor barrier over concrete, overlapped 8", including concrete covered by vinyl, VCT, terrazzo or tile.[1]
  • COREtec Pro recommends 6-mil poly over concrete, with taped seams overlapped at least 4" and run 2" up the wall.[3]
  • AHF requires a 6-mil poly moisture barrier over concrete.[6]
  • Mannington ADURA advises against 6-mil poly directly under its floating products, and points to ASTM F3010 mitigation systems when moisture is above its limits.[4]

Over wood subfloors, Pergo doesn't require a vapor barrier,[1] and COREtec says not to put sheet plastic over wood at all.[3]

Seams

How the seams go together depends on the material.

  • Poly film overlaps: 8" for Pergo, at least 4" and taped for COREtec over concrete.[1][3]
  • Foam pad butts. On Mannington laminate, don't overlap the sheets; butt the edges and seal them with tape.[5]
  • Products with a built-in overlap: Roberts Black Jack has a 3" overlap and adhesive strip.[8]

Thickness and firmness

Thicker isn't better under a click floor.

  • Soft underlayment and soft substrates weaken the locking system and reduce indentation resistance.[3]
  • Underlayment under a floated wood floor should have a published compression resistance that meets the flooring's minimum requirements.[9]
  • Carpet pad is not underlayment. Pergo, Shaw, Mannington and AHF don't allow installing over carpet.[1][3][4][6]

Step by step

For laminate without attached pad over concrete:[1]

  1. Test the slab for moisture. See Subfloor moisture testing.
  2. Lay 6-mil poly, overlapping seams 8" (or per your maker).
  3. Roll out one layer of foam underlayment, butting seams and taping them.
  4. Install the flooring. Don't let the underlayment bunch at the walls.

Common mistakes

Most underlayment problems show up as bounce or broken locks.

  • Pad under attached-pad planks where the maker says no.
  • Two layers of foam.
  • Carpet pad under a click floor.
  • Skipping the vapor barrier over concrete where it's required.

Underlayments we carry

These are foam underlayments for laminate and engineered wood without attached pad.

Roberts markets these for laminate and engineered wood. Check the flooring maker's rules before using any of them under vinyl plank.

References

  1. Pergo: Installation essentials (laminate)
  2. Pergo Extreme installation
  3. COREtec Pro installation guidelines
  4. Mannington: ADURA Max installation
  5. Mannington: Laminate installation
  6. AHF: Rigid core installation
  7. NALFA: Laminate flooring FAQs
  8. Roberts Black Jack underlayment (product page)
  9. NWFA: Wood Flooring Installation Guidelines
  10. Roberts Serenity foam underlayment (product page)
  11. Roberts Unison 2-in-1 underlayment (product page)

Linked PDF documents are archived copies saved by PreFloor Tools so they stay available if the publisher moves or removes them. Check the publisher's website for the latest revision.

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