Using Exterior Paint Indoors

Using exterior paint inside the home is a common mistake made by DIYers and amateur painters. At first glance, interior and exterior paints may seem interchangeable. But there are good reasons why exterior and interior paints are formulated differently. Using exterior paint indoors can lead to strong odors, health risks from VOCs, poor adhesion, and other issues.

Using Exterior Paint Indoors

Key Takeaways on Using Exterior Paint Indoors

  • Always read paint can labeling – only use paints in recommended locations.
  • Ventilate aggressively after applying exterior paint indoors to allow VOCs to dissipate.
  • Primer and repaint interior surfaces with interior grade paints for best results.
  • Monitor pets and sensitive individuals carefully for irritation symptoms.
  • Hire professionals for the most thorough exterior paint removal and repainting.
  • Dispose of unused exterior paint cans properly according to local hazardous waste guidelines.
  • Limit future mistakes by clearly labeling exterior paint cans after purchase.

While convenient and readily available, exterior paints simply have no place inside occupied residential and commercial structures. Follow these tips to safely remove exterior paint and improve your indoor air quality.

Overview of Main Concerns with Exterior Paint Indoors

While using exterior paint inside is not highly dangerous, it is certainly not recommended. Here are some of the main problems that can occur:

  • Strong Odor – Exterior paints contain higher VOCs and chemicals that resist mold and mildew. These additives produce a very strong and unpleasant odor when used indoors.
  • VOC Off-Gassing – The VOCs from exterior paint will continue emitting at high levels as the paint cures. This can cause eye, nose and throat irritation along with headaches or dizziness.
  • Poor Adhesion – Exterior paints are formulated for surfaces like stucco, brick and siding. They may not properly adhere to drywall, plaster or wallpaper.
  • Flaking/Chipping – Since exterior paints don’t flex as well indoors, they are prone to flaking or chipping over time. This looks unsightly and requires repainting.
  • Longer Cure Time – It takes exterior paints much longer to fully cure and stop emitting VOCs when used inside. This prolongs odor and off-gassing issues.
  • Higher VOCs – Some exterior paints contain more VOCs than interior paints, as they are designed for outdoor use. VOCs should be minimized indoors.
  • Unnecessary Additives – The mold/mildew additives are not needed indoors and introduce unnecessary chemicals.

While letting exterior paint dry as-is is an option, properly fixing the issue involves repainting for best results and indoor air quality.

Dangers and Health Risks of VOCs

VOC stands for volatile organic compounds. VOCs are carbon-containing chemicals that easily evaporate at room temperature. High VOC exposure has been linked to the following health risks:

  • Headaches, dizziness, nausea
  • Throat and eye irritation
  • Exacerbation of asthma symptoms
  • Liver, kidney, and central nervous system damage
  • Increased risk of cancer

VOCs are common in paints, stains, varnishes, wax, adhesives and other building products. Exterior paints in particular have higher VOCs since they are designed to withstand outdoor elements.

When exterior paint is used indoors, the VOCs have nowhere to disperse. As the paint cures, it will continuously emit VOCs into the indoor air over a long period of time. The VOC concentration builds up and causes severe discomfort and health issues for building occupants.

Sensitive groups like children, pregnant women, the elderly and those with respiratory issues are most vulnerable to VOC overexposure. Using exterior paint indoors poses the greatest risk to these populations.

Steps to Fix and Remove Exterior Paint Used Indoors

Once you’ve applied exterior paint on interior surfaces, what is the proper way to fix it? Here are the recommended steps:

1. Ventilate the Space

The first step is to ventilate the area as much as possible after application.

  • Open all windows and doors
  • Run exhaust fans at full speed
  • Use box fans in doorways to circulate air
  • Consider setting up a window air conditioner to ventilate and provide airflow
  • Use HEPA air filters and purifiers to filter VOCs

This will allow much of the initial VOC off-gassing to leave the home. Ventilate the space for at least 24-48 hours after applying the paint. The longer the better.

2. Prime Over the Paint

Once the exterior paint dries, apply an interior primer over the paint. This seals in any remaining VOCs from off-gassing further. Be sure to use a high-quality, low-VOC primer specifically designed for interior use.

Priming also improves adhesion for the new layer of interior paint. Make sure to use an appropriate primer for the surface material (drywall, plaster, etc). Apply two coats of primer and let fully dry.

3. Repaint with Interior Paint

After priming, the final step is to repaint the entire surface with high-quality interior paint. This completes the sealing process and gives your walls a fresh coat of paint formulated for indoor use.

When selecting interior paint, look for zero-VOC or low-VOC options. Avoid oils-based paints and go for latex or acrylic-based. Water-based paints are lower in VOCs.

Apply two to three coats of top-quality interior paint. Allow each coat to fully dry before adding another. Once repainted, the hazardous exterior paint will be safely covered up.

4. Air Out Property During and After Painting

Be sure to keep ventilating the property during and after painting. Open windows and use fans to circulate air as primer and new paint is applied.

After repainting, allow fresh paint to cure for at least 48 hours with open windows. The new interior paint will also off-gas slightly. So continue ventilating for a few days after finishing.

5. Dispose of Paint Cans Properly

Don’t forget to properly dispose of the exterior paint cans, primer cans and any painting supplies. Check local household hazardous waste guidelines on how to safely dispose of half-used paint cans and other chemical products.

Solutions for Already Dried Exterior Paint Indoors

What if you realize weeks or months later that exterior paint was improperly used inside your home? Here are some solutions if the paint has already dried:

  • No action is needed if occupants are not bothered by odors. Since the paint has cured, any potential VOC hazards are gone. Simply repainting the walls for aesthetics would be fine.
  • Strong odors may linger for a very long time for certain types of exterior paints. If this is the case, apply an interior primer followed by interior paints.
  • If the exterior paint is flaking or chipping, repair damaged areas then prime and repaint the entire surface.
  • Hire a professional painting company to strip the exterior paint and properly repaint affected rooms. This provides the most thorough fix.
  • As a simpler option, have painters apply new primer and paint without fully removing the existing coating.

The key is adding new layers on top of the dried exterior paint to control odors and improve appearance. Fully stripping the paint is ideal but not absolutely necessary in all cases.

Typical VOC Content: Exterior vs. Interior Paint

Why does exterior paint have higher VOCs? Here is a look at typical VOC levels for exterior vs. interior paint from major brands:

Paint TypeTypical VOC Content
Exterior Latex Paint50-300 g/L
Interior Latex Paint0-50 g/L
Exterior Oil-Based Paint300-400 g/L
Interior Oil-Based Paint100-300 g/L

The indoor air quality standard for non-flat paints is a maximum VOC content of 150 g/L. For flat ceiling paints, the limit is 50 g/L.

As shown above, many exterior paints far exceed these limits. But quality interior paints specifically comply with these VOC restrictions through better formulations.

Some exterior paints like Behr Premium Plus Ultra line advertise lower VOCs around 50 g/L. But even paints with lower VOCs are not made for indoor use. Sticking with true interior paints is always the wisest choice indoors.

Health and Odor Issues from Specific Exterior Paint Brands

Here is a look at some top exterior paint brands and the potential issues that can occur if used indoors:

Behr Exterior Paint

  • Very strong odor during curing phase, lasting 3-7 days on average
  • Eye, nose and throat irritation reported if used indoors
  • Higher VOCs than Behr interior paints

Sherwin Williams Exterior Paint

  • Oil-based exterior paints have high 300+ g/L VOCs
  • Duratapex exterior has 97 g/L VOCs, still above indoor limit of 50 g/L
  • Resilience line has VOCs around 50 g/L but optimized for exteriors

Benjamin Moore Exterior Paint

  • Worst odor noted from MooreGard mildew-resistant exterior paint
  • Higher VOCs than their interior Regal Select paints
  • Sticks well to interior surfaces but takes weeks to fully cure

Valspar Exterior Paint

  • Reserve Line – This includes zero-VOC tintable bases like Reserve Flat and Reserve Satin. However, even zero-VOC still means it’s designed for exterior use.
  • Solid Hide – The standard Solid Hide line of enamels, flats and satins have VOCs ranging from 50-100 g/L.
  • Duramax – Higher end options like Duramax Flat have VOCs around 100 g/L after tinting.
  • Professional – Professional grade enamels and elastomerics can have 150+ g/L VOCs. Designed for heavy commercial use.

Olympic Exterior Paint

  • Woodland Oil – The high-end Woodland Oil semi-transparent stain contains VOCs around 380 g/L. Emits strong odor.
  • ONE – The ONE line has zero-VOC tintable bases. But the resins still cure slowly indoors and require ventilation.
  • Premium – Options like Premium Flat and Satin have VOC levels around 50-100 g/L post tinting.
  • Storm Proof – Their mold/mildew resistant Storm Proof Paint poses indoor air quality risks if used inside.

Using Exterior Paint in Specific Rooms in a House

Using exterior paint indoors is not advised for any room. But some rooms require even more caution due to their function and ventilation.

Exterior Paint in Bathrooms

Bathrooms are the most hazardous place to use exterior paints. The moisture level leads to excessive mildew and mold growth indoors. To combat this, bath paints include additives that inhibit mold and mildew.

Many exterior paints also include these additives at even higher concentrations. Using exterior paint in bathrooms can leach these chemicals into steam and moisture. This leads to greater inhalation and exposure risk.

Additionally, bathrooms have limited ventilation. Trapping exterior paint VOCs in a small, humid bathroom is dangerous. It allows concentrations to build up rapidly.

If exterior paint was wrongly used in a bathroom, thorough repainting is highly recommended. Hire professionals to strip paint to fully remove additives.

Exterior Paint in Kitchens

Kitchens also have elevated humidity and cooking byproducts in the air. Any VOCs from exterior paint will mix into food particles and steam.

In kitchens, exterior paint VOCs also risk contaminating food prep surfaces. Use extreme caution and repaint any surfaces that contact food.

Kitchen ventilation is often limited to a range hood.Complement with open windows or external ventilation to reduce VOC levels. Kitchen cabinets painted with exterior paint should be replaced or refinished.

Exterior Paint in Living Spaces

For living spaces like bedrooms, living rooms and finished basements, the health risks are lower. These spaces have more air volume and better ventilation.

But odor and curing issues will linger much longer throughout an entire home’s living space. Off-gassing exterior paint in living areas require diligent ventilation day and night.

Living spaces should still be primed and painted over with interior paints. But this can be carefully done room-by-room to spread out cost and labor.

Special Concerns for Exterior Paint Indoors with Pets

Pet owners must take extra precautions when using exterior paints in homes with dogs, cats, birds or reptiles. Pets face higher health risks from airborne VOCs.

Dogs and cats have a more sensitive respiratory system. They develop eye, nose, and throat irritation faster when interior air quality declines. Keep pets outdoors as much as possible during and after application.

Birds and reptiles are even more vulnerable. Off-gassing paint fumes can quickly sicken or kill a pet bird or reptile if their cage or habitat is inside the home. Again, find alternative housing for pets until VOCs disperse.

Once interior levels are safe for humans again, they should also be safe at similar levels for pets. But continue to monitor animals closely for any irritation or discomfort.

How Long Does Off-Gassing Last from Exterior Paint?

A key question is how long does exterior paint keep emitting VOCs when used indoors? This depends on the specific paint product’s VOC level and composition.

Here is a general timeline for off-gassing and curing of exterior paint applied indoors:

  • Initial off-gassing: Highest VOC emissions occur in the first 48-72 hours as paint dries. Ventilate aggressively during this period.
  • Odor dissipation: Lingering paint odors usually go away within 5-7 days as more VOCs get released. But it takes 2-4 weeks for odors to fully disappear in some cases.
  • Curing completion: Exterior paint can take 4-6 weeks to fully cure and harden when used indoors. Curing time depends on humidity, temperatures, and ventilation.
  • Fadeout of VOCs: The last remaining VOCs get released over 4-8 weeks after application. But concentrations become very low past the first 1-2 weeks.

Again, these are rough estimates that vary by exact product. The key is keeping indoor areas well-ventilated for at least 1-2 months after application.

Is Exterior Paint Safe Once It Dries?

Is exterior paint safe to leave on walls after it dries and cures? In most cases, yes the hardened paint itself is safe if properly applied as directed.

However, potential issues that remain even after exterior paint dries:

  • Lingering paint odors from off-gassing for weeks to months
  • Irritation if dust from dried paint is inhaled
  • Chance of poor adhesion leading to future flaking and chipping
  • Presence of unnecessary mold-resistant additives indoors
  • Lower quality aesthetics compared to interior paint

So while dried exterior paint on walls is not hazardous if left alone, it is still advisable to apply an interior primer and paint. This provides a cleaner, healthier interior environment.

Can Exterior Paint Be Used in Interior Spaces Like Closets?

For confined interior spaces like closets, basements, and hallways, using exterior paint is strongly discouraged. These spaces have limited ventilation. Trapping VOCs and odors in a confined area makes concentrations escalate rapidly.

However, some sources claim spaces like closets and basements are fine for exterior paint since natural lighting is also limited. Since exterior paints resist fading, they will retain color even with minimal light exposure.

But the health risks outweigh any potential benefits. Stick with top quality interior paints only in these types of interior rooms without windows or ventilation. The CIR safety report concludes exterior paint should never be used in confined indoor spaces.

Is It Okay to Use Exterior Paint on Interior Trim, Molding and Doors?

Applying exterior paint to interior trim, crown molding, baseboards and doors is another practice to avoid. These surfaces are “breathing zones” where people are closest to off-gassing VOCs.

Some painters wrongly assume trim takes more abuse and should be coated in durable exterior enamel paint. While exterior trim paints are tougher, they are unsuitable for interior wood trim and doors.

Instead, use interior grade trim paints in satin, semi-gloss or high gloss sheens. Top brands like Sherwin-Williams offer durable interior trim paints for high-traffic areas.

Can Exterior Paint Be Used in a Garage or Shed?

Attached or detached garages, sheds and outbuildings are suitable spaces to use exterior grade paints. These structures resemble outdoor environments.

The risks come when exterior paints used in garages or sheds off-gas into interior living spaces. Be sure to isolate garage or shed air flow during and after painting.

Close doors and seal any vents or ductwork. Ventilate the outdoor structures themselves to allow VOCs to dissipate outdoors.

Exterior paints are also fine for interior walls of detached sheds or workshops. Just take care to allow proper curing time before use. Wear a respirator when entering until odors disappear.

How to Dispose of Leftover Exterior Paint

When tackling an interior painting project using exterior paint, you’ll likely have leftover paint. The EPA recommends these steps to properly dispose of oil-based or latex exterior paint:

  • First allow paint cans to air dry completely with lids off. The local hazardous waste center may require paint to be dried out before acceptance.
  • For liquid latex paint, mix in an absorbent material like cat litter or sawdust until it forms a thick, doughy paste. Allow paste to dry fully.
  • Place lids back on dried out paint cans and transport to the local hazardous waste disposal center. Many communities have special collection days.
  • If no hazardous waste center is available, put dried paint cans in normal household trash. Remove lids so trash collectors can see paint is dried out.
  • Leftover primers, thinners, strippers and cleaning solvents also require special disposal. Follow same process to allow drying fully before disposal.

Never pour excess exterior (or interior) paint down drains, into storm sewers, or directly onto the ground. Dried out paint cans can be safely landfilled without environmental risk.

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