Laminate

Patching and Skim-Coating Under Resilient

Choosing and using cement-based patch and skim coat under resilient flooring: primers, thickness limits, wood subfloors, and wait times.

Updated · 2 min read

Patch and skim coat fill the small stuff: trowel ridges, scratches, joints, old adhesive lines and low spots that are too small for a self-leveler. Resilient flooring shows everything underneath it, so the patch job often decides how the finished floor looks.

Cement-based vs gypsum

Most resilient manufacturers want a cement-based patch because it's stronger.

  • Portland and calcium aluminate patches are the standard. Mapei Planipatch, for example, is a polymer-modified cement-based patch.[3]
  • Gypsum is inherently weak, so it's limited to dry interior areas.[1]
  • AHF allows Portland, calcium aluminate or gypsum products, but the patch must reach at least 3,500 psi compressive strength.[4] Check the flooring maker's requirement before you pick a patch.

Primer or not

Whether you prime depends on the substrate and the product. Here is how ARDEX Feather Finish handles it:[1]

  • Normal, porous concrete: no primer needed.
  • Gypsum or very absorbent concrete: prime (ARDEX calls for P 51 double prime or P 4).
  • Metal and non-porous surfaces: a primer made for them (ARDEX P 82).

Mapei Planipatch needs no additive or primer over clean, porous concrete, and can go over existing sheet vinyl, VCT and cement terrazzo.[3] Every system is different, so read the bag.

Thickness limits

Skim coats are made to feather out, but they all have a maximum depth.

Product Range Over
ARDEX Feather Finish True featheredge to 1/2" Concrete and other approved substrates[1]
ARDEX SKM Featheredge to 1/2" Untreated plywood, plus concrete[2]

For anything deeper or wider, use a patch rated for depth or a self-leveling underlayment.

Step by step

The process is simple; mixing and timing are where it goes wrong.

  1. Clean the substrate: sound, dry, and free of dust, oil and loose adhesive.
  2. Prime if the product and substrate call for it.
  3. Mix with the exact water the bag specifies. ARDEX Feather Finish takes 2 1/2 quarts per bag and has a 15 to 20 minute pot life.[1]
  4. Apply with a flat trowel, pressing hard for the first pass and feathering the edges.
  5. Let it harden, then scrape or lightly sand ridges before the flooring goes down.
  6. Wait the specified time. Feather Finish can take resilient flooring once it hardens, typically in 15 to 20 minutes. Wait 16 hours before wood flooring or epoxy and urethane adhesives.[1]

Common mistakes

Most patch failures trace back to the wrong product or rushing the next step.

  • Adding extra water to extend working time. It weakens the patch.
  • Patching over dust or old adhesive. The patch comes loose, and the floor with it.
  • Going past the depth limit. Thick skim coats crack and shrink.
  • Using gypsum patch in wet areas. Keep it interior and dry, if the flooring maker allows it at all.

Products we carry

These are the patches, primer and trowels we carry for this job.

References

  1. ARDEX Feather Finish technical data
  2. ARDEX SKM technical data
  3. Mapei Planipatch
  4. AHF: Dry-back LVT and VBT installation instructions

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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