Preventing Mold and Mildew Under Laminate.
Why This Matters
Mold and mildew can cause huge health problems, especially in a basement, but how does it get there? Concrete is porous. It naturally releases moisture and if it gets trapped against your underlay and the laminate, it creates the perfect condition for mold and mildew growth.
What can Lead to Mold and Mildew?
Mold and mildew have a better chance to develop if:
- There isn't a sufficient moisture barrier
- Moisture gets trapped in the underlay and can rot sections
- The floor is installed in a basement or on slab-on-grade concrete
- Moisture levels in the concrete were never tested or addressed before installation
- Spills or leaks are allowed to seep into seams and remain trapped
How to Prevent Mold and Mildew
1. Test the Concrete for Moisture First
Use a moisture meter or perform a calcium chloride test before you install. This ensures you know the risk level before laying your floor. A quick and easy way to check a concrete floor for moisture is to use a plastic sheet. Tape a 18"x18" or 24"x24" sheet of polyethylene plastic to the concrete surface and seal the edges with tape. After 24-72 hours, check under the plastic for condensation or darkening of the concrete. If moisture is present, it indicates a potential moisture problem
2. Always Use a Moisture Barrier or Subfloor System
A 6 mil plastic sheet is the bare minimum. A dimpled subfloor membrane or anything that creates an air gap to allow moisture to evaporate.
3. Expansion Gaps
Leaving an expansion gap ensures the floor has space to move with temperature and humidity changes, which helps prevent trapped moisture. Follow your laminate manufacturer’s recommended gap size to allow airflow and prevent buckling.
4. Clean and Dry Spills Immediately
Even small spills can seep into seams and create a breeding ground for mold if left untreated.
How Airflow Under the Floor Helps
Flat foam underlay or plastic sheets can trap moisture directly against the underlay and laminate floor. A dimpled subfloor membrane lifts the entire flooring assembly off the concrete and creates an air space that allows air circulation and moisture to evaporate instead of letting it collect under your floor.
In Summary
Stopping moisture or water is near impossible, but you can control it. The best way to prevent mold and mildew damage, don't give it a breeding ground. Test your concrete before you start and use the right underlay. Ideally use something with an air gap that will naturally and safely let moisture evaporate.