Exterior vs Interior Paint: What Is the Difference?

Exterior paint is made to withstand sun, rain, wind, heat and cold. Interior paint is made to be washable, look good and not smell too much. You should not use interior paint on a façade, because it fades, cracks and peels much faster.

What exterior paint has to withstand

An outside wall gets everything. By day it can be in strong sun, at night it gets cold. On rainy days it gets soaked and then dries out. The wind brings dust and, near the sea, salt.

That is why exterior paint usually contains ingredients that protect against UV rays, which fade colours, and against water. Many also have additives against mould and algae. The film it forms must be flexible, to keep up with the wall as it expands and contracts.

What is different about interior paint

It is designed to be cleaned with a cloth or sponge without being damaged.
It has less smell and gives off fewer fumes, because it is used in enclosed spaces.
It does not need to resist UV or rain.
It can become brittle or lose colour outdoors.

If you use interior paint outside, the film is weak. It can blister after a few months of rain and the sun will take the colour out of it.

And the other way round: exterior paint indoors?

That is not a good idea either. Exterior paint can have a stronger smell and release more fumes for longer. Indoors, with the windows closed, that is unpleasant. Use each paint where it was designed to be used, unless the label says it is suitable for both.

What to read on the label

Before buying, read the tin carefully. Manufacturers state where it can be used, how much area it covers, the drying time and how to thin it.

Check that it says "exterior" or "interior and exterior".
Check the type of surface: render, concrete, brick, or metal and wood.
Check whether it states resistance to algae and mould, if your wall is damp.
Check the coverage per litre, to work out how many tins you need.
Check the application conditions, such as minimum temperature and humidity.

Primer and finish coat

On new walls, weak render or repaired areas, a primer is usually needed before the finish coat. The primer helps the paint bond and use less paint. If the wall is dusty or crumbling, there are primers designed to bind the surface. Follow the manufacturer's recommendations.

On façades, water-based paint is widely used, as it is easy to apply and the tools can be cleaned with water. For metal gates and railings or for exterior woodwork, specific products are used, which are not the same as masonry paint.

Matt, satin or gloss finish

On façades, a matt finish is the most common, because it hides small flaws in the render. Glossier finishes show imperfections more, but are usually easier to clean. It is a matter of taste and of the condition of the wall.

Tip: Ask in the shop whether the paint you have chosen suits your type of wall and the climate where you live. Always buy tins from the same batch for the whole façade, so the colour does not vary from one wall to another.