You must sand between coats to improve the adhesion between the surface and paint. So, do you need to sand between coats of polycrylic?
You must sand between coats of polycrylic to remove dust particles and smoothen the surface for the next coat. Sanding also creates tiny ridges that the next coat can penetrate and stick to.
However, you must use fine-grit and not coarse-grit sandpaper. That’s because coarse sandpaper will remove the entire finish, while fine-grit sandpaper will only smooth the surface and make it ready for the next coat.
If You Don’t Sand Between Coats:
If you don’t sand between coats of polycrylic, the next coat won’t adhere properly. That’s because while polycrylic coating is drying (2 hours), the dust will settle over the wet coating. So if you apply the next coat, the dust will prevent it from sticking properly.
Sanding removes the dust, evens out the surface, and creates tiny scratches for the next coat to stick to. Polycrylic has a thin coat, so the surface must be even before applying it.
Sanding between coats is more important for high-gloss polycrylic. That’s because when dry high-gloss sheen has a glossy layer that repels liquid, including the new polycrylic coat. So, you must remove the high-gloss topcoat, and then apply the next coat.
Sanding Before Applying Polycrylic
You must sand a surface before applying polycrylic. That’s because polycrylic has a thin coating, and the surface must be even (flat) before applying it. Sanding will even out the surface, remove dust, and help the coating to stick better.
However, if the surface is clean, even, and has no imperfections, then sanding is optional. That’s because as long as the surface is in good condition, the sealant will stick.
For non-porous, or surfaces with imperfections, sanding is mandatory. That’s because polycrylic doesn’t stick to non-porous surfaces, such as glass. So, you must sand a non-porous surface and create scratches to help it stick.
It’s important to clean the surface with a clean rag to remove the produced dust from sanding.
Sanding The Last Coat of Polycrylic
You shouldn’t sand the last (final) coat of a polycrylic finish because it will remove the glossy topcoat, leaving the finish exposed to water and moisture. If the top layer of the polycrylic finish is removed, the surface underneath won’t be protected from weather elements.
Polycrylic is a topcoat that protects surfaces from moisture, water, scratches, and other damage. When dry, it forms a glossy finish that repels (prevents) liquid from penetrating its surface. Since water (or liquid) can’t penetrate its glossy finish, the paint and surface underneath are protected.
But, if you sand the glossy finish off, the moisture-resistant layer will get removed. So, water (or liquid) will penetrate and damage the paint and surface underneath the finish.
However, you can sand the final coat with ultrafine-grit sandpaper (600-grit). The ultrafine-grit sandpaper will smooth out the polycrylic finish and remove bumps or imperfections from the surface.
You can also sand the final coat if you plan to paint or seal it. For instance, if you want to seal the polycrylic with another sealer, such as polyurethane, you must sand (remove) the glossy finish so the next sealant coating can stick.
How To Sand Polycrylic Between Coats?
Sanding between polycrylic coats isn’t hard, but you must use the right type of sandpaper. To sand it, use fine-grit sandpaper (220-grit). If you use coarse sandpaper, you will remove the entire finish.
Here’s how to do it:
- Wait until the coat dries (2 hours).
- Clean it with a clean rag.
- Using fine-grit sandpaper, sand the whole polycrylic coating.
- Remove the dust produced from sanding.
- Apply the next coat.
- Do the same for all coats (except for the final coat).
To know if the polycrylic is dry enough for sanding, swipe sandpaper over the coating. The coating isn’t dry enough if the sandpaper gets clogged. However, if the sandpaper moves smoothly over the coating, you can sand it.
Painting Over Polycrylic Without Sanding
You shouldn’t paint over polycrylic without sanding. That’s because polycrylic has a glossy finish that repels liquid, including paint. So, if you apply paint over it, the paint won’t stick and will peel off.
Paint must penetrate (soak into) the surface to stick. But, since polycrylic prevents liquid from penetrating its surface, the paint can’t soak into the surface and won’t stick. This leads to a tacky (wet) paint finish.
Even if the coating is old (varnished) and doesn’t repel paint (very unlikely), the coating would be dirty and dusty, so sanding before painting over it is always necessary.
Sanding polycrylic will create tiny scratches on the coating that the paint can soak into. But, the adhesion between the paint and the surface won’t be good. So, the best way to apply paint over it is to remove the top layer or the entire finish.
Number of Coats
You must apply 3 coats of polycrylic on a surface to increase the durability and resistance of the surface against water, moisture, or scratches.
Less than 3 coats won’t give the surface enough protection because the polycrylic finish is light and thin. Also, applying more than 3 coats will create a thick coating, creating an uneven surface. So, you must apply 3 coats.
However, you must wait until one coat dries, sand it, and then apply the next one. You shouldn’t apply all 3 coats at the same time as that will increase the dry time and can ruin the finish. It takes polycrylic 2 hours to dry between coats.
Sanding between coats of polycrylic will improve the bonding between the surface and polycrylic and help the finish to be more durable. Sanding removes imperfections, dust, and bumps from the surface, leaving behind a smooth and even surface for the next coat to stick to.