Sanding removes imperfections and bumps from the surface, allowing the paint to stick to an even and clean surface. So, should you sand latex paint?
You must sand latex paint if you are painting over a bumpy surface. The bumps or imperfections will prevent the paint from sticking properly. However, sanding will remove those imperfections.
You must also sand if the surface is painted or sealed because the existing finish will prevent the new coating from sticking. Sanding will remove the glossy layer of the sealer and create tiny ridges for the paint to stick to.
Latex Dry Time Before Sanding
You must sand latex paint after it has fully dried, which takes 3 hours. Latex paint is water-based, so it dries faster than most paints.
To dry, the solvent (water) of the paint must evaporate. Once the solvent evaporates, the paint particles start to harden, and the coating becomes rigid. Once the finish is rigid, you can sand it.
If you sand before the latex paint has dried, you will ruin the finish. If the solvent isn’t evaporated and the particles haven’t hardened, the coating will be wet and weak so the sandpaper will remove it rather than smooth it.
To know if the finish is dry enough for sanding, feel the texture using your hand. If the finish feels dry and textured, it means it has dried, and you can sand it. On the other hand, if the coating texture feels wet and it sticks in your hand, it hasn’t dried (yet), and you can’t sand it.
You can also use fine-grit sandpaper to know if the finish is dry or not. Swipe it over the coating; if the sandpaper starts to clog, it means the paint isn’t dry yet. If it goes smoothly over the coating, the paint is dry, and you can sand it. You must use fine-grit sandpaper for this and not coarse sandpaper.
Sanding Between Coats
Sanding latex paint between coats isn’t mandatory. However, it will help the paint to stick better and provide a smoother finish.
While the latex paint coating is drying, dust and nibs will settle over it. If you apply the next coating without sanding, its finish will have bubbles on its finish (because of the dust).
Sanding will remove the dust and other imperfections from the existing coating and allow the new coating to stick to a smooth and even surface. As an alternative, you can use a clean rag to remove the dust from the finish and then apply the next paint coating.
Sanding The Last Coat
You shouldn’t sand the final coat of latex paint because the last coat will reveal the color of the finish. If you do it, the finish will look discolored and scratched.
Except for bumps in the coating, sanding also removes some layers of the paint. So, if you sand the last coat, you will remove its bright shade. As a result, the finish will look old and scratched. Also, it will weaken the finish and cause the coating to peel off (wash off) easier.
But, you can sand the final coating of latex paint if you will apply a sealer over it. Since most sealers are clear coats (have no color), they will reveal imperfections and bumps on the surface. So, sanding will remove the imperfections from the surface and allow the sealer to stick properly.
Sanding Before Applying Latex Paint
To get a better finish, you must sand before applying latex paint. Though latex paint has impressive bonding qualities, it won’t stick properly to a dirty surface. So, sanding will remove the imperfections (and dirt) from the surface and create a smooth layer for it to stick to.
Also, you must sand if the surface is already painted or sealed. That’s because the latex paint won’t stick to oil-based paint or sealer. A sealer, such as polyurethane, forms a glossy and thick layer that repels moisture, including paint. So, if you apply latex paint over a sealed surface, the glossy layer of the sealer will prevent it from penetrating and sticking.
However, if the surface is painted with water-based paint, you can apply latex paint without sanding. But, the surface must be even and have no imperfections. If that’s the case, you must clean the surface with a clean rag, let it dry, and then apply the paint.
Final Words
Overall, sanding latex paint is necessary if the surface is dirty, dusted, or uneven. It will remove the imperfections from the surface and help it stick better. Also, if the surface is painted with oil-based paint or sealer, you must sand it before applying it.
To sand between coats of latex paint, use fine-grit sandpaper. Fine-grit sandpaper won’t remove the paint coating; instead, it will smoothen the layer. To sand before applying latex paint, use coarse-grit sandpaper. Coarse sandpaper will remove the old finish and even out the 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,