What to Put Under Commercial Gym Flooring

The short answer is: While you can often install rubber directly on concrete, commercial durability requires a targeted approach. You must use specific underlayments based on moisture risks (vapor barriers), noise control (acoustic layers), or subfloor protection (kraft paper).

In my role overseeing gym flooring production, I constantly see projects fail not because of the rubber quality, but because the subfloor prep was ignored. A commercial gym is a high-stakes environment; you are battling hydrostatic pressure, structural vibration, and heavy impact loads. To give you the immediate answers you need, I have compiled a Material Summary Table below. This is your "cheat sheet" for determining what goes under your floor.

Underlayment Material	Primary Function	When to Use It
Vapor Barrier (6-mil Poly)	Moisture Block	Ground-level concrete; damp basements; "green" concrete.
Acoustic Underlay	Noise Reduction	2nd-floor gyms; mixed-use buildings (above office/retail).
Shock Pad	Impact Absorption	Heavy lifting zones (Olympic lifting, Cross-training).
Kraft/Rosin Paper	Chemical Barrier	Installing over leased hardwood/vinyl (prevents staining).
Self-Leveling Compound	Surface Flatness	Uneven, cracked, or pitted subfloors (prep before underlay).

Now that you have the quick overview, we need to determine exactly which category your facility falls into using a logical decision process.

How Do You Decide What Underlayment is Necessary?

You need to follow a simple 3-step decision tree: Check for moisture on ground floors, check for acoustic requirements on upper floors, and check for heavy impact zones. If any answer is "Yes," a specific underlayment is mandatory for system integrity.

When I consult with engineers on site, we don’t guess; we follow a strict diagnostic logic. You can use this same workflow to determine your requirements instantly:

Step 1: The Moisture Test (Ground Floor/Basement)

• Question: Is your concrete slab "sweating," or does it have high relative humidity (RH)?
• Decision: If YES → You must install a Vapor Barrier.
• Why: Trapped moisture rots adhesives and breeds mold under the rubber—a risk detailed in our guide on can mold grow under rubber gym flooring.

Step 2: The Acoustic Test (Upper Levels)

• Question: Are there tenants or sensitive areas underneath your gym space?
• Decision: If YES → You must install Acoustic Underlayment.
• Why: Concrete transmits vibration; your neighbors will hear every dropped dumbbell without it.

Step 3: The Impact Test (Lifting Zones)

• Question: Will athletes be dropping weights over 100lbs (45kg) repeatedly?
• Decision: If YES → You need Shock Pads or thicker tiles.
• Why: To prevent the concrete slab itself from cracking under kinetic load.

Once you have identified your needs, the next logical question is: how do you combine these layers effectively?

What Is the Best Flooring Setup for Your Specific Scenario?

The "best" setup depends entirely on your facility type. For ground floors, prioritize moisture defense; for upper floors, prioritize acoustics; for lifting zones, prioritize shock absorption. Below are the standard professional "stacks" we recommend for durability.

In manufacturing, we talk about "system stacks"—the specific combination of layers that work together. Using the wrong combination (like a soft acoustic mat under a heavy lifting platform) can cause instability. Here are the three most common and effective B2B configurations:

Scenario A: The "Ground Floor Commercial" Stack

• Best for: Commercial gyms on concrete slabs, garages, warehouses.
• The Stack:
  1. Subfloor: Concrete Slab (Leveled).
  2. Layer 1: 6-mil Polyethylene Sheeting (Vapor Barrier).
  3. Layer 2: 8mm – 10mm Rolled Rubber Flooring.
• Insight: This is the industry standard often referenced when asking what to put under commercial gym flooring—it’s cost-effective and protects the rubber from rising damp.

Scenario B: The "Upper Level / Luxury" Stack

• Best for: Hotel gyms, 2nd-floor fitness centers, corporate wellness.
• The Stack:
  1. Subfloor: Concrete or Plywood.
  2. Layer 1: Commercial Acoustic Underlayment (Bonded Crumb/Foam).
  3. Layer 2: 8mm – 10mm Rolled Rubber (Glued to underlayment, or taped).
• Insight: This minimizes structure-borne noise complaints. Ensure the underlayment density is high to prevent squishiness.

Scenario C: The "Heavy Lifting" Stack

• Best for: CrossFit boxes, Olympic lifting platforms.
• The Stack:
  1. Subfloor: Concrete.
  2. Layer 1: 10mm – 20mm Impact Shock Pad.
  3. Layer 2: 30mm – 50mm Rubber Tiles (Interlocking).
• Insight: Never use thin rolls here. You need mass to absorb energy and protect the building’s foundation.

However, none of these stacks will work if the foundation itself is flawed. This brings us to the most overlooked aspect of preparation.

Does Underlayment Fix Uneven Subfloors?

No, underlayment will not fix an uneven floor; it will actually "telegraph" imperfections to the surface. You must use self-leveling compound or grind the concrete to ensure the subfloor is flat within 3/16 inch over 10 feet before installing any mats.

A common misconception among first-time gym builders is that a thick rubber mat will hide a bumpy concrete floor. From my production experience, I can tell you the opposite happens. Rubber is flexible. If there is a divot or a ridge in the concrete, the rubber will conform to it.

• Telegraphing: This is when the texture or defects of the subfloor show through the finished floor. It looks unprofessional and creates tripping hazards.
• Gap Issues: If the floor is uneven, the seams of your rubber rolls will not align flush. You will have gaps that collect dirt and sweat.
• The Solution:
  • For Low Spots: Use a commercial-grade Self-Leveling Compound (cementitious binder) to fill voids.
  • For High Spots: Use a concrete grinder to knock down ridges.
  • Tolerance: Aim for a flatness tolerance of 3/16" per 10 ft radius. This is the industry standard for a professional install.

Now that we have prepped the floor, let’s revisit protecting the subfloor itself, particularly in leased commercial spaces.

How Can You Prevent Damage to Leased Hardwood or Tile?

To protect expensive finished floors in leased spaces, you must use a "sacrificial layer" like Kraft paper or red rosin paper. This prevents plasticizer migration, a chemical reaction where rubber permanently stains wood or vinyl finishes.

If you are leasing a space that was previously a showroom or office with nice hardwood floors, you are liable for that floor’s condition. The biggest danger isn’t scratches; it’s chemistry. Most gym flooring is made of SBR rubber, which contains plasticizers. When these sit directly on wood varnish or vinyl, they migrate out of the rubber and create a permanent yellow/brown reaction.

• The Fix: Lay down distinct rows of Kraft Paper or Red Rosin Paper (taped at the seams) before laying your rubber mats.
• Why it works: It creates a chemical break. The rubber touches the paper, not the wood finish.
• Cost: It is incredibly cheap insurance compared to the cost of sanding and refinishing a 5,000 sq ft hardwood floor upon lease exit.

We have covered what to use, but safety dictates we must also cover what to strictly avoid.

Which Materials Should Commercial Gyms Strictly Avoid?

Commercial facilities must strictly avoid residential carpet padding, cardboard, and low-density foam. These materials compress under heavy loads, create unstable lifting surfaces, and can trap moisture leading to bacterial growth.

I sometimes see facility managers trying to cut costs by using materials available at local home improvement stores. This is dangerous. In a commercial setting, "compression set" is a critical metric.

• Carpet Padding: It is designed for footprints, not 1000lb leg press machines. It will crush permanently, leaving your floor uneven.
• Cardboard: It absorbs sweat and creates a breeding ground for silverfish and mold. It degrades within months.
• Soft Foam (Yoga Mats): Creating a "squishy" floor is dangerous for lifting. If an athlete is squatting heavy, they need a firm base. Soft underlayment causes ankle instability and potential injury.
• The Rule: If you can easily pinch the underlayment flat with your fingers, it is likely too soft for under heavy gym equipment.

Conclusion

Subfloor preparation is not the place to cut corners. Whether you need a simple vapor barrier for a garage gym or a multi-layered acoustic stack for a luxury club, the right underlayment ensures your investment lasts for decades.

Author Bio

I am a Gym Flooring Production Manager with extensive experience in the technical engineering and manufacturing of sports surfaces. My work focuses on bridging the gap between factory production specifications and real-world installation challenges, helping facility owners build safe, durable, and compliant gym environments.

If you are struggling to choose the right "stack" for your specific facility, or need advice on subfloor leveling requirements, contact our technical team today. We can review your blueprints and provide a tailored recommendation or a sample kit.