If either lacquer or wax are present, strip them before proceeding. Do this before and during application to evenly blend the ingredients that control sheen and UV resistance. Apply thin coats. Thick ones take longer to dry and are more likely to drip or wrinkle.
Dust interferes with adhesion and leaves unsightly bumps in the finish. Use a cloth dampened with mineral spirits on oil-based finishes; use a water-dampened cloth on water-based finishes. A dry microfiber cloth also works well with both finishes. Shaking creates bubbles, which leave a rough, pitted surface.
It's okay to shake wipe-on polys, however. Thinning doesn't improve adhesion, and you'll have to apply more coats and use more solvent. Use natural bristle for oil-based finishes and synthetic filament polyester, nylon, or a blend of the two for water-based and water-based oil-modified finishes. Don't use rollers or foam brushes—they create bubbles.
Your brush will be easier to clean, and will go longer between cleanings, if its bristles are dipped first in mineral spirits, if you're using an oil-based poly, or in water, if the finish is water-based.
Before using the brush, rapidly roll the handle between your hands inside a cardboard box to eliminate excess. Working from a separate container prevents the dust and other particles picked up by the brush from contaminating the finish in the can. After dipping about one-third of the brush into the finish, gently slap it against the inside of the container.
Scraping the bristles over the edge of a container leaves the brush too dry to apply a coat of the right thickness. It's the best way to work the finish into the wood pores and ensure an even appearance.
Wipe the wood with a damp cloth to raise the fibers; after the surface dries, knock them back with grit sandpaper. It leaves behind tiny bits of steel that you can't see—until they rust.
Use sandpaper instead. Cookie banner We use cookies and other tracking technologies to improve your browsing experience on our site, show personalized content and targeted ads, analyze site traffic, and understand where our audiences come from. By choosing I Accept , you consent to our use of cookies and other tracking technologies. All About Polyurethane.
By Thomas Baker. Pinterest Email Pocket Flipboard. What Is Polyurethane? Oil, Water or Both? Oil-based: Turns slightly amber, which warms up a wood's color. Forms a hard, durable film in a few coats.
Dries more slowly than water-based polys, so there's a longer wait between coats. Higher in VOCs than water-based finishes and therefore not available in all parts of the country. Cleans up with mineral spirits. Water-based: Looks like milk in the can but dries crystal clear. Good if you're trying to preserve a wood's color. More watery than oil-based polys, so more coats are needed.
Dries quickly. Lower in VOCs than oil-based finishes but still requires good ventilation during application. Cleans up with soap and water. Never use ammonia-based cleaners on the cured film. However, note the following differences:. But if you really need a sealer that can handle stronger stuff—such as daily, vigorous use or lots of foot traffic—oil-based polyurethane is your best bet. And if your finished piece will be exposed to high temperatures or moisture on a regular basis, oil-based polyurethane is definitely superior.
You have the choice to spray or brush on polyurethane and polycrylic. Polyurethane is very flammable while wet, so it requires careful storage to prevent a fire. As it is, polycrylic and polyurethane are good for many of the same projects, including desks, side tables, picture frames, and dressers.
If you need a tiebreaker, ask yourself the following when deciding which one to use include:. It's best to apply polyurethane to flat as in level surfaces so the finish can self-level and is less likely to drip.
When applying polyurethane on vertical surfaces, you may experience drips or runs. Minimize this problem by applying thinner coats or by switching from standard brush-on poly to a wipe-on or spray finish, both of which can be applied in very thin coats. If you end up with runs or drips, try to sand them out when sanding between coats, or carefully remove them with a sharp razor blade followed by sanding to feather in the blemish.
As you're finishing each fresh coat during application, check your work with a bright side-light. Crouch down so you see the light reflecting off of the surface. This highlights imperfections, such as bumps, bubbles, ugly brush marks, and spots that you simply missed or where the finish is too light. You can fix these problems when the finish is still wet but not once it starts to set up.
As with all wood finishes, good results depend on smooth, clean wood surfaces, but this goes double with clear finishes such as polyurethane. Sand your wood with at least grit sandpaper. For open-grain woods like oak , ash, or walnut , you can apply a wood grain filler before the polyurethane, to create an ultra-smooth finished surface.
Clean the wood very thoroughly to remove sanding dust before each new coat of polyurethane, using a vacuum if available and a tack cloth. You can also use a rag moistened with mineral spirits for an oil-based poly or cheesecloth moistened with denatured alcohol for a water-based poly.
You may choose to thin oil-based polyurethanes with mineral spirits or naphtha, but for most applications, this is not necessary; check the manufacturer's recommendations on the product label. Thinning can help the finish flow into fine details and nooks and crannies with less buildup. Apply oil-based poly using a fine-bristled brush natural or synthetic bristles or a foam brush.
Avoid inexpensive bristle brushes, as these tend to leave obvious brush strokes. Foam brushes are inexpensive and disposable and work well for most flat surfaces. Bristle brushes are better for molded edges and fine details. Brush on the polyurethane so the brush strokes are parallel to the grain of the wood. Use a sufficient, but not overly thick, coat of finish. Complete each area with long, straight strokes to brush out as many bubbles as possible.
The few remaining bubbles will typically disappear within moments. After the first coat has fully dried according to the manufacturer's directions , lightly sand the entire surface again, parallel to the grain , using grit sandpaper.
The polyurethane will sand easily, so be careful not to sand through the thin coat and damage the stain or wood underneath. Remove all dust with a vacuum and tack cloth before applying the second coat. Repeat these steps until the desired level of protection is achieved. For protection, two coats are the minimum, but floors and anything else that will see hard wear or occasional moisture should get at least three coats. Each coat also makes the finish a bit smoother.
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