When it comes to installing epoxy or polyaspartic flooring, most people focus on the look—the high-gloss finish, the flake blend, the bold metallic swirls. But before any of that can happen, there’s something far more important happening beneath the surface: moisture control.

At Polzin Epoxy Designs, we’ve seen countless floors that looked beautiful on day one—but peeled, bubbled, or discolored within a year due to one issue: moisture vapor rising through the concrete.

That’s where a moisture vapor barrier (MVB) comes into play. In this blog, we’re going to explain exactly what an MVB is, why it matters, and how we use it to create long-lasting, problem-free coating systems—even in Wisconsin’s challenging climate.

Whether you’re a homeowner coating a garage, a business owner upgrading a commercial space, or a contractor comparing systems, understanding moisture mitigation is crucial. Let’s break it down.

Concrete Is Not Waterproof—And It Was Never Meant to Be

Concrete looks solid, but it’s actually a porous material. Water can pass through it in vapor form, especially when there’s moisture in the ground beneath a slab.

In Wisconsin, we see it all the time: a garage slab that’s 10, 20, even 30 years old, still allowing moisture vapor to rise up through the concrete. The source might be:

• Seasonal ground moisture

• Poor drainage

• Lack of a proper vapor barrier under the slab

• Hydrostatic pressure from a high water table

• Snow melt from vehicles in the winter

And here’s the catch: epoxy and polyaspartic coatings are impermeable. Once they cure, they block moisture from escaping the surface. If vapor continues to rise through the concrete, it has nowhere to go—so it pushes back against the coating. That’s when you see:

• Blistering

• Delamination (peeling)

• Discoloration

• Bubbles or pinholes

This is not a product failure—it’s a substrate condition that needs to be addressed.

What Is a Moisture Vapor Barrier (MVB)?

An MVB is a specially formulated epoxy primer that’s designed to resist moisture vapor transmission from beneath the concrete slab. It’s not a waterproofing system, but rather a breathable membrane that reduces vapor transmission rates to a safe level for coatings.

Think of it like an airlock between your concrete and your floor coating. It allows moisture to stay where it belongs—within the slab—and protects the finish on top.

At Polzin Epoxy Designs, we use high-performance MVBs that are moisture-tolerant, self-priming, and designed for compatibility with our full coating systems. They’re applied after mechanical prep but before the decorative layers (flakes, metallics, or color coats) go down.

How We Test for Moisture (And Why We Always Do It)

Before we install a single flake or pour any epoxy, we test the concrete for moisture.

There are several industry-standard ways to do this:

1. Calcium Chloride Test (ASTM F1869)

This measures the moisture vapor emission rate (MVER) in pounds per 1,000 square feet per 24 hours. If the rate exceeds manufacturer specs (often 3–5 lbs), an MVB is required.

2. Relative Humidity Probe (ASTM F2170)

This measures RH levels inside the concrete slab. Most coatings require RH levels below 75–85% to be considered safe without an MVB.

3. Visual Inspection & Surface Readings

Though not as scientific, we also look for signs like efflorescence, discoloration, or previous coating failure. A surface moisture meter gives real-time data but is only one part of the equation.

Even if there’s no standing water, vapor transmission can still ruin a coating. So we don’t guess—we test.

Why MVBs Are So Important in Wisconsin

Our region presents a unique set of challenges:

• Freeze/thaw cycles put pressure on slabs and increase microcracking, allowing more moisture movement.

• Snow, ice, and road salt in garages melt and reintroduce water to the surface daily in winter.

• High water tables in spring and fall can raise hydrostatic pressure.

• Lack of vapor barriers under older homes or outbuildings is common.

For us, MVBs aren’t a rare add-on—they’re a crucial part of building a reliable, long-lasting system.

What Happens If You Skip the MVB?

If moisture is present and no MVB is used, your floor may look good for a few months—or even a year—but eventually, the symptoms will show.

Imagine this: you walk into your garage and notice the coating has lifted in a few small areas. A month later, those areas are bigger. It starts to look like blisters or even peeling paint. The floor feels spongy in spots. It’s no longer bonded.

At that point, the fix isn’t a touch-up—it’s a full removal and reinstallation, often including mechanical re-prep and reapplication of the entire system.

Using a moisture vapor barrier on the front end is a tiny investment compared to the cost and hassle of floor failure.

Common Misconceptions About Moisture and Epoxy

Let’s address a few myths we hear often:

❌ “The concrete’s old, so it shouldn’t have any moisture.”

Age doesn’t guarantee dryness. Many older homes were built without underslab vapor barriers, meaning they’ve always been drawing moisture.

❌ “It’s a heated garage, so moisture won’t be a problem.”

Heat may reduce surface dampness but does nothing to stop vapor transmission from below. In fact, warm slabs can sometimes increase vapor drive.

❌ “I didn’t see any water, so I don’t need an MVB.”

Vapor is invisible. You won’t see it until the coating fails—unless you test for it properly.

How We Apply MVBs as Part of a Professional System

Here’s a simplified look at how we incorporate moisture vapor barriers into our full coating process:

1. Mechanical Prep We grind or shot blast the concrete to open up pores and create the required CSP (Concrete Surface Profile), ensuring the MVB can penetrate and bond.
2. Moisture Testing Using the methods described earlier, we test the slab to determine if moisture levels exceed safe thresholds.
3. Apply MVB Primer If needed, we roll or squeegee on a specialty moisture vapor barrier epoxy. This layer penetrates the surface and chemically bonds with the concrete.
4. Re-Inspection After curing, we check for proper adhesion and coverage.
5. Continue with Coating System From there, we proceed with flake broadcast, metallics, or color coats, followed by a polyaspartic or urethane topcoat.

The result? A floor that’s not only beautiful but also engineered for long-term durability.

Where MVBs Are Commonly Used

Moisture vapor barriers are standard in many of our projects, especially:

• Garage Floors

• Basements

• Commercial Kitchens

• Veterinary Clinics

• Warehouses

• Retail stores

• Bathrooms or Laundry Rooms

• Outdoor Entryways with Covered Concrete

Any space where water exposure, high humidity, or slab-on-grade construction exists is a candidate for moisture mitigation.

Final Thoughts: Floor Prep Isn’t Just About Aesthetics

Too often, homeowners and even some contractors focus on the finish—the color, the texture, the sheen. But what determines a floor’s performance over time has more to do with what’s underneath.

Skipping an MVB on a moisture-prone floor is like painting over rust. It might look good for a little while, but you’ll be dealing with failure sooner than you’d like.

Our philosophy at Polzin Epoxy Designs is this: do it right the first time. That means:

• Testing for moisture

• Understanding the site conditions

• Choosing the right coating system

• Using a moisture vapor barrier when necessary

It’s not just about protecting the coating—it’s about protecting your investment.

Interested in a Floor That Lasts?

If you’re planning to coat your garage, basement, shop, or commercial space, we’re here to help. We’ll assess your floor, test for moisture, and recommend a system designed for performance—not just looks.

Want to learn more or book a consultation? Contact us here and follow us on Facebook to see real project photos and behind-the-scenes insights.