Can I use exterior paint inside my house?
There are several reasons why you should not use exterior paint indoors.
First, exterior paints contain mildew inhibitors. They used to use mercury;
I'm not sure if they still do. But in any event, you DON'T want these
chemicals outgassing into your house. Knowing that interior surfaces can have the same problems as exterior surfaces, for example moisture in your bathroom or heat in your kitchen, you may want to turn towards an exterior paint to solve the problem because of its wonderful benefits of withstanding the elements, but this isn't a good solution. In fact, an exterior paint can cause more harm than good by using it indoors because of the VOC's (Volatile Organic Compounds), or what's commonly referred to as paint fumes that it gives off.
Second, exterior paints are designed to "chalk" as they weather. This is
definitely undesirable inside your house.
Third, exterior paints are formulated to be more flexible than interior
paints, because they are subjected to a much wider range of temperatures. This means that they don't dry as hard which means they'll always be a bit soft
It might seem so, but that's not the way it is. A good-quality interior latex
paint is plenty good enough for your bathroom. Use a bathroom / kitchen paint for these areas to stop mildew forming.
If you have mistakenly used exterior paint inside, there are specific things you must do before you re-paint an interior surface that was already painted with an exterior paint. A paint specialist can help, but it is usually recommended to remove as much of the old paint as possible, sand the surface, wash and dry the surface, and then apply a stain-blocking primer to the walls like KILZ before you paint. This type of primer will put a barrier between the old paint and the new paint.
Remember that an exterior paint is made to withstand the elements because the weather can cause many problems if the paint's viscosity isn't up to par. The sun can cause the color to fade, and the rain and snow can cause moisture buildup which may lead to cracking, peeling, and mold and mildew problems