Can you use normal emulsion paint outside? It's a pretty common question we get, and the short answer is 'no'. The longer and slightly more geeky answer is below, so strap in and read on...
Paint: The Basics
All paint is similar in the sense that it's made from the same four ingredients: solvent, pigments, additives and resin. The big difference for Interior vs Exterior paints is in the additives and resin used. These things affect how the paints perform under indoor or outdoor conditions.
Exterior paint has more additives, so it can withstand the weather
Difference 1: Additives
Exterior paint has different additives to make it more hardy and resist cracking, fading and mould from harsher conditions outdoors. Interior paint has some level of protection against these things, but not nearly as much because it won't be exposed to the elements.
Painting the outside is a big job, so choose a specialist paint
Difference 2: Resin
Exterior paint also uses different resins, which binds paint to the surface. For exterior paint the resin is flexible, so the paint can flex with heat expansion and contraction of materials outdoors without cracking. Interior paint doesn't need that flexibility, so it uses harder resins that make it tougher against marks and easy to clean.
Exterior paint has more Pigment so colours can withstand UV rays
Difference 3: Toxin Levels
A critical difference is that interior paint is often made to reduce VOCs as much as possible. VOCs or 'Volatile Organic Compounds' are breathable toxins released when paint is applied, which are nasty and harmful for humans. For interior paints being Low VOC is way more important because they're applied in our living spaces. For exterior paint we have less regular exposure to these VOCs because they're outdoors, so the hardiness of the paint is prioritised over being Low VOC.
Interior paint has less nasty breathable toxins
So, can I use Exterior paint indoors?
Nope. Both Exterior and Interior paints exist because they're specially formulated for the job in-or-outdoors. Interior paint used outdoors won't stand up to the elements and will look terrible pretty quickly. Exterior paint used indoors won't take the scuffs and stains of daily life and is likely to be pretty harmful in terms of VOC levels.
There are some 'multi-purpose' paints out there, but you'll always be compromising on something. So it's always better to choose the right paint for the job to get the best long-lasting result.
COAT has the perfect range of water-based Low VOC interior paint colours. Ready to shop? Browse all colours here.