Outgassing

Concrete Outgassing compared to Standard Materials

Concrete generally emits far fewer VOCs and chemical fumes than OSB (Oriented Strand Board) and standard drywall. Concrete is a mineral-based product, whereas OSB and drywall rely on chemical resins, binders, and synthetic additives. [1, 2]

A closer look at the specific materials clarifies their off-gassing potential:

• Concrete (Lowest Outgassing): Primarily made of limestone, sand, water, and aggregate, concrete releases virtually zero VOCs. While fresh concrete can expel trapped air (referred to as "outgassing" in construction when applied with sealants), it does not release the chemical fumes associated with manufactured building materials.

• OSB (Highest Outgassing): OSB is manufactured using wood strands bonded together by synthetic resins (often containing formaldehyde or MDI). These glues can off-gas VOCs for years.

• Drywall (Moderate Outgassing): The gypsum core of standard drywall is relatively inert. However, the facing paper and the adhesives used to bind it can emit low levels of VOCs. Additionally, the joint compounds and paints applied over drywall during finishing are often major sources of off-gassing. [1, 2, 3, 4, 5]

If you are aiming to minimize chemical exposure in an interior space, you can achieve the lowest VOC levels by leaving concrete exposed, using low-VOC finishes, or installing specialized materials. For further information, guides from Chemical Free House provide detailed strategies on how to safely seal off-gassing materials in your home.

Outgassing (or off-gassing) is the slow release of volatile organic compounds (VOCs) and chemicals from materials into the air. In standard building materials like composite wood, paints, and insulation, this process degrades indoor air quality and can trigger headaches, respiratory issues, and asthma over time. [1, 2]

Common residential building materials are frequent contributors to long-term chemical emissions in your home:

Major Culprits & Emitted Chemicals

• Engineered Wood: Plywood, MDF, particleboard, and laminate frequently emit formaldehyde, primarily from the petroleum-based and formaldehyde-based resins used to bind the wood fibers together.

• Carpets & Padding: Synthetic carpets, vinyl flooring, and carpet pads release phthalates (plasticizers) and VOCs from synthetic backing and adhesives.

• Paints & Finishes: Traditional paints, sealants, and varnishes contain high levels of solvents that "flash off" during drying, releasing airborne VOCs for weeks to months after application.

• Foam Insulation: Polyurethane and polyisocyanurate insulation boards release residual blowing agents and flame retardants. [1, 2, 3, 4, 5]

Why It Happens

• The "Breakdown" Process: Most materials aren't just letting off built-up surface air. Rather, their chemical structures (resins, plasticizers, binders) continually degrade and break down, especially when exposed to heat, humidity, and direct sunlight.

• Sprinters vs. Marathoners: VOCs evaporate quickly (and have that "new" smell), while semi-volatile organic compounds (SVOCs) break down slowly over many years, binding to household dust and continually re-entering the air. [1]

Mitigation Strategies

• Ventilation: The most actionable step is increasing fresh air exchange. Use localized exhaust fans in the kitchen and bathrooms, and consider whole-house mechanical ventilation systems.

• Low-Emitting Materials: When building or renovating, select products certified for low or zero VOC emissions. Look for third-party badges like GREENGUARD, FloorScore, or Scientific Certification Systems (SCS).

• Air Purification: Use high-efficiency particulate air (HEPA) filters combined with activated carbon filters, which are designed to capture and neutralize airborne VOCs and chemicals stuck to dust.

• Bake-Outs: For new builds or recently painted rooms, you can accelerate the outgassing process by raising the indoor temperature and humidity for a few days while running exhaust fans constantly to pull the chemicals outdoors. [1]

Concrete Outgassing

Because concrete is a porous, sponge-like material, it naturally absorbs and releases air and moisture. When temperatures rise or barometric pressure drops, trapped air inside expands and travels through the concrete's capillaries to the surface. [1]

While this "breathing" is normal, outgassing can cause major issues when applying barrier coatings (like epoxy, polyurethane, or paint). As the expanding air escapes, it pushes through the wet coating, creating bubbles, craters, or tiny "pinholes". [1]

Key Causes of Outgassing

• Temperature Changes: Air expands when heated. Direct sunlight, rising daytime temperatures, or the exothermic heat generated by curing coatings forces air out of the slab.

• Entrained Air: Concrete intentionally contains tiny air voids (to help it survive freeze-thaw cycles). When these voids expand, they release air.

• Moisture Vapor Transmission (MVT): As air escapes, it often carries moisture from the concrete with it, worsening coating adhesion. [1, 2, 3]

How to Prevent Coating Defects

If you are painting or sealing a concrete floor, you can prevent outgassing from ruining the finish by taking a few precautions: [1, 2]

• Coat During Cooling Cycles: Apply coatings in the late afternoon or evening when the concrete temperature is dropping rather than rising.

• Use a Primer: Apply a specialized deep-penetrating concrete primer to seal the pores before rolling on your main coat.

• Mechanically Profile: Grind or shot-blast the concrete to open pores evenly and ensure a strong bond

• So save money and keep concrete chemicalized coatings out of your home.

• Natural is always better than synthetic.  The body does not know what to do with synthetic materials so it goes berserk.