Many people find DIY projects slow, and are keen to speed them along in any way possible. When you’ve got plenty of other things to be getting on with in day-to-day life, waiting for paint, glue, primer, varnish, and other substances to dry can be a grueling process. A lot of people are tempted to rush things for this reason.
If you’ve just primed a surface, you’ve probably checked the primer can for the estimated drying time – but you might be wondering if you really have to wait this long, or if you can just slap some paint on and not worry about it. After all, some primers come mixed with paint, so do you really have to let the primer dry first?
What happens if you paint over primer too soon? If you try to paint over primer that is too wet, there is a high risk that the paint will bubble and fail to adhere to the primer properly. You may also cause the primer to pull away from the surface, ruining that coat too. Removing the paint will be challenging and you might have to start all over again. Don’t paint on primer that hasn’t dried properly.
Why Can’t You Paint Damp Primer?
The primer bonds to the surface it has been applied to as it dries, and it isn’t fully bonded until it is fully dry. This means that if you add paint to it, there’s a risk that you’ll rub it off the surface and ruin the adhesion.
Even if this doesn’t happen, the wetness of the primer will probably stop the paint from adhering properly, and may cause bubbling.
These are two separate issues, and you might encounter one or both of them, so let’s look at them separately, starting with ruining the primer’s adhesion.
Primers need to stick very well to the surface that they have been applied to, so that they can provide a solid base for the paint when you apply it. In order to stick, they need to dry for a certain amount of time, so that chemicals and moisture can evaporate from the primer, leaving it firmly bonded to the surface.
If you apply pressure or extra moisture (which will be in the paint) to the primer before it has dried, you may find that primer peels off, or doesn’t dry properly. The primer will not bind to the surface beneath, and you may be able to rub it off just by touching it. This obviously won’t allow the paint to stick well.
If this happens, you’ll probably have to sand the whole surface down, removing all of the paint and primer, so you can start from scratch. This will make the project take far longer.
In other cases, the dampness in the primer will cause bubbles in the paint. This is because the moisture needs to evaporate, but it can’t evaporate if it has been sealed beneath a layer of paint. As it tries to evaporate, it will put pressure on the paint from underneath, causing the paint to bubble up.
Even if both layers successfully dry after this point, the surface of your paint will have stretched and pockets will have formed underneath it, preventing it from sticking to the primer properly. Bubbled paint will not look good, either, and you won’t get the smooth, glossy finish you are probably seeking.
How Do You Tell When Primer is Ready to be Painted?
The best way to check whether primer is ready to paint is to touch it firmly with your finger. If you get traces of primer on your skin, it isn’t yet ready to be painted. The same is true if it still feels tacky. You may want to wait about 30 minutes after it no longer feels tacky before you apply paint to it.
Primer drying times can vary enormously, so it’s best to look at the primer’s can to find the estimated drying time in normal conditions. Oil-based primers usually take a lot longer to dry than water-based or latex primers. Oil-based may need around 15 hours to dry, while the other two will usually be dry in about 6 hours.
You should also be aware that if the primer is in a room that is cold or damp (or both), it’s going to dry more slowly than in a warm, dry spot. Bear this in mind if you’re priming surfaces during the winter, or in a damp room. It could as much as double the drying time.
Even in a suitable space, waiting for primer to dry might add a frustrating amount of time to your project, but it’s still worth doing. Primer massively improves the adhesion of your paint and will make the finished surface look better. It’s worth the additional time investment in most cases.
Do You Have to Paint Over Primer as Soon as It’s Dry?
Generally speaking, no. Most primers can be left for several days, or even as long as a month, before they must be painted over. However, the longer you leave them, the more dust will accumulate on the surface, and the more the primer will deteriorate and lose its strength.
It’s therefore best to paint over primer as soon as you can, particularly on certain surfaces. Metal primers, for example, should be painted as soon as they are dry, and will need to be re-primed if they are left for more than 2 weeks without being painted. Most concrete primers must be covered within 7 days.
Wood primers may last as long as 30 days without painting, but it’s still preferable to paint them much sooner. On the whole, applying the paint within 24 hours of the primer drying will give you the best results.
Painting over primer too soon will generally lead to the paint bubbling and failing to stick to your surface. In some cases, it will also ruin the primer, and you’ll have to completely strip the project and begin from scratch. You should always let primer thoroughly dry before you paint it.