Do you have to sand between coats of polyurethane?

person sanding polyurethane

If you are working with wood, chances are strong you will need to pull out a stack of sandpaper at some point and put it to work. You may be wondering if you need to sand every layer of polyurethane. The truth is sanding between layers may help to make the piece of furniture look better but will not make or break your project.

Let’s start with the basics to answer this question and help you to get the best-looking project. We will discuss all the different aspects that can affect a project with polyurethane. Beginners may be surprised by how many steps are involved in making a wood project perfect.

What is Polyurethane?

Polyurethane is a synthetic resin that’s used as a varnish for woodwork. What makes it such a good option is it’s transparent and resistant to mold, mildew, fungus, water, and abrasions. Moreover, it dries quicker than other types of varnishes, and you can get it in matte or glossy sheens.

Next, polyurethane comes in both water or oil-based options. Water-based polyurethane is more environmentally friendly with less noxious smells but not as resistant to wear or tear. Oil-based polyurethane smells horrible because of toxins and VOCs but lasts longer. Always wear protective gear with oil-based polyurethane, including a respirator mask, gloves, and protective clothing. Also, make sure you are in a well-ventilated area.

Oil-based polyurethane is easier to apply because it’s thicker as it has more solid compounds. Water-based polyurethane just cannot achieve the same level of shine and gloss as its oil-based counterpart. However, oil-based polyurethane takes longer to dry and is prone to brush marks. Finally, water-based polyurethane looks milky when wet but dries clear, while the oil-based has a slight reddish-amber hue, but this helps to accentuate the wood grain.

Materials

Gather your supplies before you start your project. You will need a vacuum, sandpaper of varying grits, a sander, mineral spirits, the polyurethane, a brush or roller, lint-free cloths, and cleaning agents.

How to Apply Polyurethane

Applying polyurethane is a fairly straightforward process. Some believe you need to sand between layers to help them stick to the previous later, but that’s not true; it’s simply to ensure the layers are level.

Before Applying Polyurethane

The most important step is to remove as much dust as possible, not just from your project but from the room, you are working in too. Vacuum everything first, and make sure to vacuum after sanding layers too. Next, make sure your project is clean and smooth. For larger surfaces, you may want to power wash first. Allow the surfaces to completely dry before starting.

If you plan to stain your wood, you will want to do that before you apply the polyurethane. Allow it to dry completely before going to the next step. If you plan to use oil-based poly over water-based poly, make sure you sand the surface to ensure the finish sticks well. Use either rough sandpaper or steel wool to get the job done.

First Coat

To get started on your project, you will want to put the first layer of polyurethane and thin it with paint thinner. The thinner allows the finish to dry faster so you can get to sanding faster. Wait until the wood is dried and cured to sand, which takes about a full day. Start with very fine grit and sand with the grain of the wood. Remove the dust before adding another layer.

Other Coats

Depending on the level of shine and protection you want, you will add between one to three additional coats of full-strength polyurethane. It’s best to sand between each layer as it will help to level out the layers, but you do not need to stand to make the layers stick. If you are sure the layers are even, you can sand very lightly or skip completely. Make sure to allow each layer to dry and to apply as thin a coat as possible to avoid leveling issues. Wait one to two full days to allow the thin layers to cure and harden.

Last Coat

For the final coat, you do not need to sand the polyurethane. Simply allow it to harden, and then you can apply a paste wax or protective wax to finish off the job. But the wax into the wood with a soft dry cloth and wait half an hour for it to set and buff for a beautiful shine. Reapply every 6 to 12 months. You can also use wipe-on poly if you prefer and then use the finest grit sandpaper for a smooth finish.

How Many Coats is too Many

Adding more than three coats will increase the cost of the project without offering any real benefits to your project. More layers mean more costly polyurethane and more work for you, too, along with more of your time and dealing with a space you can not move around freely. The surface could also peel or turn yellow if you use too many coats as they oxidate. Stick with three coats unless you are a professional.

Benefits of Polyurethane

Polyurethane has many benefits as it’s very versatile and works on a variety of surfaces. First, it’s the perfect option for heavy traffic areas as it’s very strong and resists abrasion from impact better than any other option available. Second, it’s resistant to oil and chemicals, meaning if you spill something on the floor, it should not ruin your finish. Third, polyurethane can handle more weight from furniture or even cars, and it’s still flexible enough to work for the garage or even the kitchen table.

Final Thoughts

While sanding between layers of polyurethane is not a technical necessity, it’s definitely a good practice to ensure your project is level and looks its best. Sanding, while not a fun process, helps to give you a high-quality finish ready to last for years and look beautiful.