While applying multiple coats of a paint or sealant, DIYers are advised to sand between coats for proper adhesion. But do you have to sand between coats of primer?
You don’t need to sand between coats of primer because primers have good adhesives meaning that each primer coating will stick to the existing coat without sanding. However, if you are working with oil-based primer, it’s advised to sand lightly between coats using 320-grit sandpaper.
This is because oil-based primers dry slowly and can take up to 4 hours to dry enough for re-coat. This leaves enough time for dust and debris to settle on the existing oil-based primer coat. In this case, you need to sand the dust nibs off of the existing coat before a recoat.
This post reveals more about the need for sanding between coats of primer including cases where you must sand. Let’s dive in.
How Long Should Primer Dry Before Sanding?
If you need to sand between coats of primer paint, allow each primer coat to dry for at least 60 minutes before sanding with 320-grit sandpaper. This gives each primer coating plenty of time to harden enough to handle the sandpaper grit.
If you sand primer coating too soon, you’ll wear the coat and remove it because it wouldn’t be strong enough to handle the sandpaper grit. To know for sure how long to wait before sanding a primer coat, check the manufacturer’s instructions.
Though sanding between coats of primer isn’t always needed, you’ll need to do it sometimes, especially when using oil-based or enamel paint primer. However, before you can sand a primer coat, the coat needs to have hardened enough so it can handle the sandpaper grit. How long it takes for the primer to get that strong depends on the type of primer.
On average, it takes around 60 minutes for primer to dry enough for sanding. But, to be on the safer side, you should wait 2 hours before sanding especially if you applied the primer coating in cold temperatures.
Should You Sand Between Coats of Oil-based Primer?
You should always sand between coats of oil-based primer paint because oil-based primer dries slowly and absorbs dirt.
So, you need to sand the dirt off the existing coat using fine sandpaper so the next coat can bond strongly to the existing coat. Applying multiple coats of oil-based primer isn’t advised due to the thickness of the primer paint.
When purchasing your gallon or can of oil-based primer paint from the hardware store, kindly ask the storekeeper to hand you a pack of 320-grit sandpaper too. This is because you’ll be sanding between coats of the oil-based primer during application. Oil-based primer contains a high of synthetic or natural oils. As such, the primer coat takes some time to dry and can take over 4 hours to fully dry.
While the primer is drying, dust and debris that are carried by the wind will fall and stick on the wet oil-based primer coating, these contaminants dry with the primer coat. To allow the next coat to sit well, you need to remove these contaminants and dirt with sandpaper.
You should also know that oil-based primers have good coverage due to the thick nature of the primer. This means that you don’t need to apply many coats of oil-based primer. In most cases, a coat is enough.
Should You Sand Between Coats of Water-based Primer?
You don’t need to sand between coats of water-based primer because water-based primer dries quickly and doesn’t allow dust to settle on it. Also, water-based primer paint has a textured finish when it dries which allows the next coat to bite into and stick to the existing coat.
However, if you are applying the water-based primer coat in a dusty environment like a construction site, you need to sand between coats.
Unlike oil-based paint primers, water-based paint primers dry quickly. On average, you can recoat water-based primer in less than 30 minutes. This leaves very little time for debris or dust to settle on the existing coat.
Since there is no debris or contaminant on the existing coat, you don’t need to sand the primer coat. If you are taking on a full renovation of your apartment or you are applying the water-based primer on a construction site, you’ll need to sand between coats.
This is because in these cases, you would be working in a dusty environment and wood shavings, sawdust, grain, and dust nibs can easily fall on the water-based primer immediately after application. So you’ll need to sand to remove the contaminants.
Related Read: Oil-Based Primer vs Water-Based Primer
Do You Have To Sand The Last Coat of Primer?
You should always sand the last coat of primer before applying the paint or sealant. This is because the last primer coat has to be textured to allow the sealant or paint to stick strongly. If you don’t sand the last coat of primer, there will be weak adhesion between the paint/sealant and the primer coat.
After applying the final coat of primer paint, you have to wait for it to dry and then sand with fine sandpaper. The purpose of sanding is to create tiny ridges in the primer coating for the paint to bite into. When this happens, the paint or sealant will stick strongly to the primer coating. Sanding the final primer coat also helps to remove dust and paint pimples on the primer coating.
If you don’t sand the final coat of primer, then the paint will not bite into the primer coating leading to weak adhesion between the paint and primer coating. The paint will stick initially but may begin to crack and chip off after a few months. You should sand the final primer coat with fine sandpaper.
Do You Need To Sand Before Applying Primer?
Sanding is usually not required before applying primer because primers are designed with adhesives that allow the primer to stick to virtually any surface without sanding.
Before applying primer paint, the only thing you need to ensure is that the surface is completely dry and in good condition. As long as the surface is dry and even, you can apply primer without sanding.
Primer paints are preparatory coats that are used on the bare surface before applying the finish or paint. Since the primer paint is usually applied to bare surfaces, manufacturers always include adhesives in the primer paint to allow it to stick to just about any type of bare surface.
As a result of this, sanding isn’t needed before applying primer but it increases the chances of getting a smooth finish. So, sanding before applying primer wouldn’t hurt.
What Happens If You Don’t Sand Between Coats of Primer?
Honestly, if you don’t sand between coats of primer paint, nothing will happen except you are working with oil-based primers. Since oil-based primers dry slowly and absorb dirt while drying, you’ll need to sand between coats. If you don’t, the primer will develop problems.
As explained earlier, primer paints have adhesives that allow the primer to stick well to just about any type of surface. So, if you don’t sand between coats of the primer coating, the primer will still stick because of the presence of adhesives.
However, if you are working with oil-based primer paints, you may end up with a bumpy primer coating if you don’t sand between coats. The bumpy texture will be caused by dirt on the existing oil-based primer coating that wasn’t sanded off. Asides from oil-based primers, you can apply other types of primers without sanding between coats.
What Grit Sandpaper Should You Use To Sand Before and Between Coats of Primer?
Before applying primer paint, you should sand the surface with 150 grit – 220-grit sandpaper. These grits are coarse enough to remove bumps and existing finishes on the surface. To sand between coats of primer paint, you’ll need finer sandpaper and 320-grit always works fine between coats. 320-grit will buff the primer coating but the sandpaper is not strong enough to remove the primer.
Before applying the first coat of primer on a surface, you need medium-grit sandpaper to remove imperfections on the surface. For instance, before applying primer on wood, you need to remove and seal nail holes, splinters, bumps, and the like on the wood. 150-grit sandpaper will do this for you. After using the 250-grit sandpaper, you can finish the surface with 220-grit sandpaper to make it smooth for the primer coat.
However, while applying the primer, you can’t use 150-grit or 220-grit sandpaper between coats because these grits are too coarse for the primer coating. Using such grit between coats of primer will remove the primer coating. To sand between coats, you need super fine sandpaper like 320-grit sandpaper. This grit is safe to use between coats but you should be careful while sanding the primer so you don’t over-sand.
In summary, you usually don’t need to sand between coats of primer because primers stick to anything as long as it’s dry and even. However, when working with oil-based primers, you’ll need to sand between coats to remove the dust that settled on the oil-based primer while it dried.
To know for sure if you need to sand between coats of a primer, check the manufacturer’s instructions or how-to guide. You should remember to sand the final coat of primer so the paint or stain can stick smoothly.