Interior paints aren’t expected to handle harsh environments and changing temperatures, so they don’t have many additives. Exterior paints, on the other hand, are infused with mildewcides and fungicides to help them resist fading in sunlight.
The interior and exterior painting contain pigment for color, a solvent or base for mixing, and additives to preserve the paint. They also contain resins to bond the ingredients to the surface being painted.
Pigment
The pigments are the finely ground material that gives paint its color. They are natural or synthetic, and can include plant, mineral or animal materials.
Pigments are the key ingredient in all paints, and they contribute to both wet hide and dry hide. The most common pigments are titanium dioxide, which contributes to a paint’s whiteness, and zinc oxide, which provides durability.
Exterior paint must withstand moisture and huge temperature changes. That’s why the resins in these types of paint are stiffer. This helps to cut down on smearing and scuffing, as well as fading and chipping.
Resins are the binding agents that hold all of the other ingredients together into a dry film on your home’s surface. They are the key ingredient that directly relates to a paints performance characteristics, including adhesion, washability and scrub resistance.
Resin
Paints contain resins to bind the pigment and additives together. Different resins provide different properties, which affect the way the paint behaves.
Resins used in exterior paint are much softer than those used in interior paint. This is because the exterior paint must survive being exposed to moisture and huge temperature changes. It also needs to combat fading, mildew and fungal growth.
Paint for the inside of a home is not subject to any of these issues, so it doesn’t need as robust a resin. This allows it to be formulated with additives that aren’t suitable for the outside, such as fancy textures and colors. In addition, it can be formulated with lower amounts of volatile organic compounds (VOCs), which are better for indoor air quality.
Solvent
Interior paint needs to be scrubbable and stain-resistant in order to handle kids, pets and other messes that are bound to happen. It must also be washable so that roller and brush marks, as well as smudges caused by furniture can be easily removed. This type of paint should also have a low or zero VOC level, which is important to preserve air quality within the home and lessen health risks.
VOCs (volatile organic chemicals) release fumes that can be toxic if inhaled. This is why most latex paints are lower in VOCs than oil-based paints. Real Milk Paint has a low VOC level, and when mixed with Outdoor Additive, can be used on exterior surfaces as well. This helps bridge the gap between interior and exterior paint, providing the best of both worlds.
Additives
There are a lot of paints that contain additives to help with specific tasks. Insulation additives, for instance, are used to insulate surfaces and save money on cooling and heating costs.
All paints have a basic makeup that includes resins, additives and pigments. They are all made of the same components, although some have different properties depending on what they're formulated for. Interior paint is formulated to allow cleaning and resist staining, while exterior paint is made to combat fading and mildew.
Binders are an additive that helps the paint keep its integrity and provides adhesion to the surface. They are often found in outdoor-friendly formulations, which are also added with other additives to combat the effects of different weather conditions. Mildew resistance additives are used to prevent the growth of mildew, typically in areas that are shaded or along the bottom of an exterior wall.
Finish
Paints are made for specific purposes, such as protecting walls from the elements or looking great. Extra additives make exterior paint tougher so it holds up to harsh weather, while interior paint is designed to look great and protect surfaces within your home.
In addition to pigments, solvents, and additives, exterior paints also contain resins, which help it bind to surfaces. Resins make the paint dirt-repellent and more durable. Other specialty paints such as textured or grained paints can give you a unique aesthetic stance on your facade.
Interior paints usually contain fewer solvents than those used in exterior paint, meaning they emit fewer odors and low levels of VOCs, which can cause health issues such as headaches and dizziness (short-term) or respiratory disease and liver damage (long-term). They also come in a variety of finishes such as matte, eggshell, satin, and gloss.