What Happens If I Skip Moisture Protection on a Slab?

Skipping moisture protection might save time and money upfront — but it’s one of the most common causes of flooring failure over concrete.

Even if your slab looks and feels dry, concrete naturally holds and releases moisture vapor over time. Without proper protection, that moisture becomes trapped beneath your flooring — and the results aren’t pretty.

Common Problems When Moisture Protection Is Skipped:

1. Buckling, Warping, and Gaps

Moisture causes wood, laminate, or engineered flooring to swell unevenly. Boards may lift at the edges, buckle in the middle, or separate at the seams.

2. Mold and Mildew Growth

Trapped moisture creates under foam or carpet underlays are the perfect conditions and ideal environment for moisture to rot the underlay. This leads to mold and moisture, allergens and a terrible smell. 

3. Flooring Discoloration or Delamination

Vinyl tiles and laminate flooring can bubble, swell, peel, or separate from their layers when exposed to moisture.

4. Cold, Damp Feel Underfoot

Concrete floors already feel cool, but moisture makes them feel clammy or wet — even with flooring on top.

Concrete subfloors feel cool but can also hold moisture. Without a barrier, your finished laminate, carpet, or wood flooring may feel damp, wet, or clammy year-round.

5. Voided Warranties

Most flooring manufacturers require a moisture barrier or underlayment on concrete. Skipping this step can void your warranty and leave you paying to fix or replace your flooring, again. So double the price because you're installing it twice.

What Many DIYers Miss:

  • Moisture doesn’t have to be visible to damage your floor
  • New concrete subfloors can release vapor for months as they fully cure. 
  • Basement and slab-on-grade subfloors are most vulnerable, 
  • A dry slab today doesn’t mean dry conditions during the wet and freezing months.

How to Protect Your Floor:

  • Use a vapor barrier or a subfloor system that lets your flooring breathe,
  • Test your concrete subfloor for moisture before installing your flooring, 
  • Always follow the flooring manufacturer’s guidelines for concrete installations

Bottom Line:

Moisture protection is more than an extra step, it’s essential to protect your flooring to save money long term. Skipping it might not show issues right away, but in the long run, damage is almost guaranteed.

Back to FLOORING 101 - Subfloor Preparation and Moisture Protection