[Expert advice] How multipurpose acrylic primer differs from alkyd primer

This article is about aerosol primers only: water-based acrylic products applied with a brush or a roller are a different story.

Although both primers are called multipurpose, there are significant differences between them, both in the way they are applied and in what they are used for. Let us look at this in more detail.

To begin with, an acrylic primer does not have to be used only under acrylic enamels, and an alkyd one only under alkyd enamels. Acrylic materials can be applied over an alkyd primer, and alkyd materials over an acrylic one.

Alkyd primer

Alkyd primer is a good choice for priming ferrous metals, and works on non-ferrous metals as well.

On wood, alkyd primer creates a good base that keeps the enamel from soaking into the wooden surface. Two coats of enamel are therefore enough to obtain a smooth, high-quality finish. There is a catch, though: the first coat of primer, like any paint coating, raises the grain, which has to be sanded down before the second coat of primer is applied. That means waiting several hours until the primer has dried completely, because alkyd primer that is still wet cannot be sanded.

Alkyd primer is not used as a filler primer, the kind used to hide minor coating defects before painting. It cannot be applied in a thick enough coat, it takes a long time to dry and it is very hard to sand.

It is not suitable for priming plastics because of its relatively low adhesion to them.

Acrylic primer

As a first primer coat on metal it is inferior to the alkyd one: adhesion to metals is lower and barrier protection against moisture is weaker.

Acrylic primer works well on wood: like the alkyd one, it creates a base that keeps the enamel from soaking into the wood, and it dries much faster and sands well. Priming a wooden surface with it takes far less time than with an alkyd primer.

It is well suited for priming plastics. The exceptions are Teflon, silicone and polyethylene, which cannot be painted at all, and polypropylene, which needs a special primer.

It works well as a filler primer: it can be applied in a thick coat, it dries quickly and it sands easily. That makes it a convenient way to hide minor surface defects.

Acrylic primer is widely used as a primer sealer applied over an acid etch primer.

Alkyd and acrylic primers can also be combined. For example, a coat of alkyd primer can be applied to metal for better barrier protection against moisture, and several coats of acrylic primer applied over it and sanded down to obtain a perfectly even, smooth surface.