Most paint types expire after a while. But, does paint primer expire, and how long does it last?
Paint primer does expire. Unopened paint primer will last up to 3 years. However, when opened, a can of paint primer that is sealed and stored correctly can last up to 2 years before it goes bad. Opened and un-sealed primer will go bad within 2 months.
But that’s not all. You can re-use most of the old paint primers with a simple trick that we explain down below.
Does Primer Expire?
Primer goes bad when exposed to moisture, heat, cold, or air. Moisture and air can cause mold to grow in the paint primer container if the container isn’t sealed correctly; this will make the primer expire.
Primer doesn’t go bad the same way your household groceries go. Primer doesn’t go bad based on an expiration date but on the primer’s storage conditions.
An expired primer won’t stick, dry, or cure. Also, the finish will the uneven and the primer color will be inconsistent. All these signs indicate that the primer has gone bad.
So, the primer doesn’t have an expiration (or best before) date. Instead, the primer goes bad when exposed to external elements like air, water, or dust.
After opening, paint primer lasts about 2 years. This is because paint primer is prone to air, moisture, and heat. So, once the primer is exposed to air, the paint particles will harden and the primer becomes unusable.
When you open the primer container, the primer will get exposed to airflow and the evaporation process will start. Once the primer solvent is evaporated, the primer will harden, and you won’t be able to re-use it.
An opened primer will last 2 years before the whole primer hardens and becomes unusable. However, if you store the opened primer container properly and seal it in an airtight container, the opened primer can last up to 3 years. To last longer, the primer container must be kept in a cool and dry room and away from moisture and airflow.
Using Old (Opened) Primer
You can use an old primer if it’s still in a good condition. All you have to do is to mix (or shake) the primer inside the container before use. Shaking the paint container will mix the paint chemicals.
Old primer works as well as a new primer. The only factor determining if you can still use old primer is the condition of the primer. You can use the old primer if the chemicals inside the primer aren’t affected (or evaporated).
Primer is prone to moisture, air, and heat. If the primer is exposed to moisture (water) or air, the solvent will start to evaporate, and the primer will start to harden. Also, if the primer is exposed to moisture, mold will start to grow inside the container, making the primer unusable.
To re-use an old primer, you must store it in an airtight container and a cool and dry room. This protects the primer from airflow, moisture, and heat.
But, before you use an old primer, you must do a test. Apply 1-2 coats of primer to a dispensable item and check the quality of the primer. If the primer dries and cures properly, you can use it.
Unopened primer can go bad or expire after some time in storage. That’s because the chemicals in the primer will start to lose their form after a while.
The primer container will start to deteriorate after a few months/years of storage. The deterioration of the container and the loose chemicals will make the unopened primer go bad.
On average, an unopened primer will last up to 3 years before it expires. However, the expiration time depends on the storage conditions. For example, in a cool and dry room, an unopened primer will last longer. But, if the primer is stored in a hot room with constant moisture exposure, the primer won’t last more than 1 year.
The best time to use a primer is within the first year of purchase.
How To Re-use Old Primer?
To revive a can of old primer paint, you need to shake the container and then mix the primer to remove any clumps in the paint primer. Let’s check out how to do this in detail.
1. Open The Container
First, open the primer container and inspect it. If the primer is dull and thick, you can re-use it. However, if the old primer has inconsistent color and is thin, it means it has gone bad, and you can’t re-use it.
2. Shake The Container
Close the container and shake it. Don’t shake the container too hard, as you can spill out the primer.
Since the primer is dull, the chemicals have separated and must mix before usage. Shaking the primer container helps to revive and re-mix the chemical properties inside the container.
3. Mix The Primer
After shaking the primer container, open the lid and mix the primer. To mix the primer, use a paint mixer or a turning stick. Paint mixers are more effective and faster. While mixing, ensure to mix the primer at the bottom too.
You must mix until the primer has a consistent color and flow. If you use a paint mixer, mix for 5 minutes. If you use a turning stick, mix for 10 minutes.
4. Add A Solvent
You can add solvent to water-based primers to get a consistent flow and color. Water-based primers use water as their solvent, so adding water to the primer will help to revive it. However, this doesn’t work if the primer has gone bad. This works only if the primer is still in a good condition.
Add 1/4 cup of water to 1 gallon of primer. You shouldn’t add too much water because water will over-thin the primer. Once you add the water, re-mix the primer.
You shouldn’t add water or a solvent to oil-based primer. That’s because oil-based primers use natural (or synthetic) oils as their solvent, and you can’t add them. If you add water to oil-based primer, you will ruin it.
After you are done, test the primer in a dispensable material. If the primer dries well, you can re-use it.
Primer Has Gone Bad If:
Here’s how to tell if a primer has gone bad or not:
1. Primer Container is Puffed
If the primer container is puffed or swollen, that’s the first indication that the primer has gone bad. A puffed container tells you that there are microorganisms present inside the container.
The microorganisms inside the paint container eat and feed on the primer. After feeding on the primer, these bacteria release gasses that puff or inflate the container.
The gasses released by the paint-eating bacteria ruin the primer inside the container by contaminating the chemicals in the primer. So a puffed paint primer container indicates that the primer has gone bad.
Related Read: Will Primer Fix Peeling Paint?
2. If The Primer Is Light
Primer has a thick flow. The thick flow allows the primer to cover more surfaces and imperfections. The thick nature of primer also helps to improve the adhesion between the primer and the paint.
If the primer is thin, chances are that it has gone bad. You must mix (or shake) the primer to see if the primer gets a thick flow. If it doesn’t, then the primer has gone bad.
3. Mold Inside The Container
If mold or mildew appears in the primer, then the primer has gone bad. This happens when the container isn’t well covered or sealed. Moisture (water) and air will get into the primer container, and the mold will start to grow.
If you notice mold or mildew inside the primer container, you can’t re-use the primer.
4. The Primer is Hard
If the primer has hardened inside the container, the primer has gone bad. Hardened primer means the primer has already dried and cured inside the container, so you can’t re-use it.
If the primer container isn’t sealed, the primer inside will be exposed to airflow. Since primer dries through evaporation, the primer will start to dry once exposed to the airflow. Once the primer solvent evaporates, the primer will start to harden and cure. Also, primer is formulated with additives that make it dry faster than most paints.
If this happens, you won’t be able to re-use the primer. That’s because the solvent has already evaporated, and the paint particles have hardened.
Conduct A Test
To know if the primer has gone bad or not, conduct a test. Apply a coat of primer to a disposable surface. If the primer sticks, dries, and cures properly, then the primer hasn’t gone bad.
However, if the primer doesn’t stick, dry, or cure properly, then the primer has gone bad. An expired primer will have an uneven coat, and bubbles may appear once it dries.
If you suspect the primer has gone bad, it’s best not to use it. That’s because the primer is the base coat, and if the base coat is ruined, the paint won’t stick well and will peel off.
The lifespan of the primer depends on the storage condition and whether the container is airtight. If the primer is stored in a cool and dry room with no exposure to moisture, the primer will last up to 3 years. If the primer is stored in a hot room and is exposed to moisture, the primer won’t last more than 1 year.
However, the unopened primer will last more than opened primers. That’s because opened primers are exposed to airflow, and air makes the primer solvent evaporate and hardens the primer. So, you must store primer in an airtight container to make it last longer.