Paint primer will cover imperfections and provide a smooth layer for the paint to stick to. But, do you need to sand between coats of primer?
You don’t need to sand between coats of primer because they have good bonding qualities and will stick without sanding. However, you must sand the oil-based primer with 320-grit sandpaper.
Oil-based primer has a slow dry time (up to 4 hours); this leaves enough time for dust and debris to settle over the coating. In this case, you must clean or sand off the dust before painting.
Primer Dry Time Before Sanding
Before sanding it, you must wait 60 minutes (1 hour) for the primer to dry. This gives it enough time to harden to handle the sandpaper grit. If you sand too soon, you will wear out the coating and remove it because it wouldn’t be strong enough to handle the sandpaper grit.
Just like paint, primer also dries through evaporation. The solvent (water or oil) must evaporate from the coating, so it gets dry and hard. So, the dry time will depend on the type (oil or water-based), room temperature, and humidity levels.
Use fine-grit sandpaper to know if the primer is dry enough for sanding. The coating isn’t dry enough if the sandpaper gets clogged while sanding. If the sandpaper moves freely, the coating is dry enough.
Sanding Between Coats
You must always sand between coats of oil-based primer because it has a slow drying time and attracts dust while drying. The dust can prevent new coats from sticking. So, you must sand or wash the dust off the coat using fine-grit sandpaper so the next coat can bond better.
While the primer is drying, dust and debris will fall and stick over the wet coating. Once the coating dries, removing the dust and debris with water or a clean rag is hard because they are inside the dried coating. So, the only way to remove them is to sand the coating with fine-grit sandpaper.
On the other hand, you don’t need to sand between coats of water-based primer because it dries fast and doesn’t allow dust to settle on it. Also, it has a textured finish when it dries, so sanding isn’t required.
Related Read: Oil-Based Primer vs Water-Based Primer
Sanding the Final Coat
Sanding the last coat of primer is optional, but it helps with paint adhesion. The last coat must be textured to allow the sealant or paint to stick strongly. Most primers have a textured finish, especially water-based types, but you can increase the textured finish by sanding it.
Sanding will create tiny ridges on the coating that the paint can stick or penetrate into. When this happens, the paint or sealant will stick strongly over the coating. Also, sanding will remove imperfections and dust from the final coating.
If you don’t sand the final coat of primer, the paint will still stick. That’s because primers are formulated with extra additives that help the paint to stick better over it. However, sanding will increase the bonding quality.
Sanding Before Applying Primer
Primer is formulated with extra additives that allow it to stick over all surfaces without sanding. However, to increase the adhesion quality, you must sand before applying primer. Sanding will remove imperfections from the surface, even (flat) out it, and create a smooth surface for the primer to stick to.
If the surface is uneven or finished with a sealant, you must sand it before applying primer. That’s because an uneven surface will create an uneven paint finish. Also, while primer will stick over a sealant, the adhesion won’t be good. So, it’s best to sand off the glossy layer of the sealant, and then apply primer and paint over it.
However, if the surface is even, dry, clean, and smooth, you don’t have to sand it before painting over it.
Sandpaper Grits (Types) To Use
Before applying primer, you must sand the surface with 150-220-grit sandpaper. These sandpapers are coarse enough to remove bumps and existing finishes on the surface.
Use fine-grit sandpaper (220-grit and upwards) to sand between primer coats. Fine-grit sandpaper will remove imperfections and bumps from the surface, but not the coating.
To sand the final coating, use ultrafine-grit sandpaper. This sandpaper will only smooth the surface (or coating) but won’t remove anything.
Final Words
In summary, sanding between coats of primers is optional because they stick over all surfaces. However, sanding will improve the bonding between the primer and the paint or surface.
Tony Adams
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,