Being in business for 34yrs and the fact that we want to do what's right by our clients has taught us that it is always wise to do whats right as in the end that what counts. Not who's the cheapest, what the easiest approach and why bother it's not my problem attitude.
What the inexperienced contractor won't tell you, that we will!
Installing a floating floor (such as Luxury Vinyl Plank/LVP or laminate) directly over existing engineered hardwood on a concrete basement subfloor creates a severe double-vapor barrier effect. Maryland Carpet and Tile explicitly warns against this setup due to Maryland's high relative humidity and concrete slab hydrodynamics.
The fundamental risk factors and biological/structural consequences include:
The Mechanism of Failure: Trapped Hydrostatic Moisture
Concrete subfloors constantly transmit invisible water vapor upward—a process known as hydrostatic pressure or vapor emission.
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The Sandwiched Vapor Trap: When you lay a waterproof or non-breathable floating floor (like LVP) over engineered hardwood, you create an airtight sandwich. The moisture rising through the concrete passes into the wood sub-layer but gets blocked by the new floating floor above.
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Absence of Evaporation: Normally, engineered hardwood allows a controlled amount of moisture to escape into the room's ambient air. Blocking that airflow traps moisture inside the wood core, elevating its moisture content to 100% saturation.
Major Failure Risks 1. Severe Buckling, Cupping, and Warping
As the plywood or HDF core of the engineered hardwood absorbs trapped moisture, the wood fibers expand horizontally and vertically.
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Tension Peak: Because it has no room to expand under the weight of the floating floor, the engineered hardwood will shear away from its adhesive, cup upward, or "blow out" (buckle).
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System Breakdown: As the base hardwood warps, it lifts the top floating floor, dislodging its locking mechanism and causing seams to pop, unlock, or crack.
2. Mold and Toxic Spore Proliferation
Wood fiber, organic glues, and dark, unventilated cavities provide the exact conditions needed for mold growth.
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Hidden Colonization: Toxic mold (such as Stachybotrys chartarum) will proliferate beneath the new floor long before visible signs appear on top.
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Indoor Air Quality Hazards: Air movement through expansion gaps around baseboards forces hidden mold spores and musty odors into living areas.
3. Delamination and Core Rot
Engineered wood relies on cross-ply layers bonded by adhesive resin. Constant moisture exposure causes the adhesive bonds to break down completely (delamination). The wood softens, rots, and turns into a spongy substrate that no longer supports structural loads.
4. Voided Manufacturer Warranties
Flooring manufacturers state that installing over an existing wood subfloor on concrete below grade (in a basement) violates baseline installation guidelines. If the top floor fails, claims are denied automatically.
Recommended Corrective Steps
To prevent catastrophic moisture damage, flooring professionals recommend:
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Tear Out Existing Hardwood: Rip up the old engineered wood and scrape down all lingering adhesives down to the bare concrete slab.
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Moisture Testing: Conduct a Calcium Chloride or Relative Humidity (RH) pin test to measure slab emissions.
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Vapor Barrier Installation: Lay down a minimum 6-mil polyethylene vapor barrier or an integrated waterproof underlayment directly over the concrete slab.
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Install Rated Flooring: Place a 100% waterproof product—such as Glue Down LVP or LVT with the properly rated adhesive, WPC Vinyl Plank or Porcelain Tile—directly over the protected slab.
If you want it done right, call us today for a consulation.
