People often assume that because LVP is waterproof, slab moisture is no longer a concern. The plank itself may be waterproof, but the system underneath it is not immune to hydrostatic pressure — water pushing up through a slab from the ground below.
Where it comes from
Hydrostatic pressure builds when there is water in the soil beneath a slab and no effective vapor barrier, or when drainage and grading direct water toward the foundation. That pressure can drive moisture up through the concrete continuously.
Why it still matters under waterproof flooring
- Glue-down installations can lose bond as moisture attacks the adhesive.
- Moisture trapped beneath the floor can lead to odor and microbial growth.
- High pH from slab moisture can degrade adhesives over time.
The takeaway: waterproof flooring solves spills from above, not pressure from below. Address slab moisture and drainage first; a moisture test and the right underlayment or barrier are cheap compared to a failed floor.
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