What is the difference between primer and undercoat?

While both primer and undercoat are used to prepare the surface for painting, they serve a different purpose. They are essentially two steps of one whole process. A good rule to keep in mind is – if you’re painting a bare surface, use primer. If the base has been primed or previously painted, use undercoat.

Primer paint is the first layer applied when painting a raw surface. Its purpose is to give the following coats a good base to stick to. It helps reduce the absorbency of porous materials, such as wood and concrete, so less coating is necessary to achieve a solid colour.

Primer also provides a layer of protection, preventing stains from bleeding through the topcoat and appearing on your walls. Additionally, it makes it easier to work with hard-to-paint surfaces, such as glass or metal.

As mentioned previously, undercoat paint is the coat that follows the primer. Its purpose is to improve the overall look of the topcoat and provide an even surface to work with. It ensures even and unaltered colour application and protects the base from moisture.