Should You Sand Walls Between Coats of Paint?


Painting walls is mostly a very messy job. It’s easy to make mistakes and think that you’ve ruined your walls. Whether you’re painting your own walls, or helping out a friend, you should know some basics. Should you sand walls between coats of paint?

Sanding walls between coats of paint is a great way to get rid of some imperfections that you’ve made while painting. Your paint job will look smoother but it is not 100% necessary to sand in-between coats of paint.

Whether you will sand your walls depends on the type of your paint. The drying time will also depend on the type of paint. 

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Should you sand walls between coats of paint?

Whether you’re a professional painter or like to do it yourself, it’s important to know when to sand your walls. If you never sand your walls you might end up with a bad paint job, and if you always sand it, you might ruin it.

When you’re painting a wall and notice that no matter how many coats you apply, it always looks bumpy or textured, it means that you have roller build-up. This occurs when you have too much paint on your roller. It’s easy to get too much paint on your roller, as you’re dipping it more and more into the paint tray because it stopped applying smoothly. This makes the roller thicker and less efficient, which is then visible on your walls. 

If you want to use latex-based paint over oil-based paint, you will have to sand it first. Oil-based paint has a very smooth surface, so any paint that goes over it has a hard time sticking to it. To sand your wall, take a piece of sandpaper and wrap it around a block. Make sure you lightly buff the surface of the oil-based wall to create a rough surface that the latex paint will stick to. You’re not trying to strip the wall, just rough it up a bit, so don’t go too hard on the wall. To check if you’re dealing with oil-based paint, wash a small section of the wall with warm water and detergent. Next, dab a cotton ball that has been soaked in rubbing alcohol. If the paint comes off with the cotton ball, it’s a latex-based paint and you don’t have to sand it. If the paint doesn’t come off, you have oil-based paint and you will have to sand it.

Another thing that can cause you problems besides roller buildup is roller texture. You probably won’t like the way it looks. Throughout the years, you have maybe added some texture to your walls to make them more interesting, or maybe the previous owner did. No matter where the texture came from, you can easily get rid of it by knocking it down with some light sanding. 

Should you sand between coats of latex paint?

Sanding between coats of latex paint won’t remove messy paintbrush strokes, it will completely remove the paint. 

If you are having trouble with paintbrush marks, strip your paint completely, and start over. This time, use a foam roller or add floetrol to your paint to minimize brush marks.

Even though you can’t sand walls between coats of latex paint, it is important to sand cabinets, doors, and trims between coats because that gives them a glossy finish. You will have to wait until it is completely dry to sand it. The best drying temperatures are between 70 and 80 degrees, with humidity below 70 percent.

To sand latex paint, use 120- or 150-grit sandpaper or a fine to medium flexible sanding sponge to sand fresh latex paint. For sanding cured latex paint you can use coarser grits. It takes up to 30 days for latex paint to cure hard and coarser grits will scratch or remove fresh paint. 

How long should paint dry before sanding?

To prevent any rough patches, you will have to allow your paint to dry enough so you can sand it. Rushing the process is not in your best interest. 

Water-based paints will always dry much faster than oil-based paints. The reason why is because the water in latex paints evaporates to let the paint dry, and there’s no water in oil-based paints. 

There are binders in the paint to help it hold the pigment together. Flat paints will have the least amount of binders and glossy paints will have the most amount of binders.

The flatter the paint sheen, the faster it will dry. Glossy paint will always take the longest time to dry. Semi-gloss paint is somewhere in the middle of the paint sheen scale, and they will take an average amount of time to dry.

Even though the paints will be dry enough in an hour or two to apply another coat, you should wait at least 12-24 hours before sanding and then applying another coat. Whether you will wait 12,18, or 24 hours depends on the type of your paint, so make sure to read the instructions on your paint.

To quicken the drying time, keep the temperature in the room around 72 degrees. Water-based paints will dry optimally in a room that temperature, and with some humidity.

Oil-based paints are going to dry best in a room that is above 50 degrees Fahrenheit but under 90 degrees Fahrenheit. 

Make sure your room isn’t cold, because colder temperature and too much humidity will slow down drying time for water-based paints because the water from the paint needs to evaporate for it to dry.

Turn on a fan on a low setting to keep the air circulating and quicken the drying process. 

Keeping the windows open to let fresh air in will speed up the drying process, unless it’s too hot, cold, or humid outside. 

What grade of sandpaper should I use between coats of paint?

You have to choose the right sandpaper grit to use sandpaper properly. They are categorized according to the coarseness of the abrasive particles used. 

Sandpaper is sized by a gauge number, with lower numbers signifying larger, coarser grits. That’s why 24-grit sandpaper is very coarse, while 1000-grit sandpaper is very fine.

Lower-number grit, which is coarser, is used for removing wood and other materials faster and with less effort than finer sandpaper. It does this by cutting the fibers on the material’s surface. 

Fine sandpaper removes a small amount of material, and it has the effect of smoothing the surface. Remember, the finer the paper, the smoother the surface. 

100-150-grit sandpaper is the best for sanding walls between coats of paint. It is the most often-used gauge of sandpaper grit, and it is in the medium range. For most applications, it is hard to go wrong with sandpaper grits in this range. You are able to work down difficult materials by applying more pressure to your workpiece. You can also preserve fine materials by letting up on the pressure. 

Is sanding latex paint dangerous?

Latex paints are water-based paints that contain solvents and harmful chemicals. They are safer than solvent-based paints, which can contain high levels of volatile organic compounds. 

One concerning component of latex paints is crystalline silica. There are some health risks associated with crystalline silica when sanding it. When crystalline silica gets in your lungs scarring and tuberous growths can develop. Long term exposure develops into silicosis, which develops into cancer.

When sanding latex paint, you have to wear an air respirator, not a dust mask. Dust mask won’t filter out crystalline silica.

Another thing to keep in mind is that older walls painted with latex paint contain lead and mercury, which are really toxic. 

Indoor latex paint contains formaldehyde, which the paint can outgas as it is drying. Breathing in formaldehyde can cause headaches, dizziness, and vomiting as well as irritation of your eyes, nose, and throat. 

Outdoor latex paints often contain high concentrations of other biocides to prevent mold growth. Because of how toxic they are, you should never put outdoors latex paint indoors. 

When painting with latex paint, open the windows and use a high volume fan in the window to exhaust the paint fumes. It is also important to keep the room ventilated while the paint is drying. During this period, which can be as long as 2 to 3 days, the paint can outgas noxious vapors.

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