How to Spray Polyurethane | Steps + Must-Read Tips [2023] (2023)

FAQs

How to Spray Polyurethane | Steps + Must-Read Tips [2023]? ›

To achieve the best results when spraying polyurethane, you want to try to focus on applying as thin of coats as possible. This will typically require making faster passes across the product surface, as well as using smaller fluid nozzles (1.0 – 1.4 mm typically) or air assist airless tip sizes.

To achieve the best results when spraying polyurethane, you want to try to focus on applying as thin of coats as possible. This will typically require making faster passes across the product surface, as well as using smaller fluid nozzles (1.0 – 1.4 mm typically) or air assist airless tip sizes.

You can use mineral spirits, paint thinner, or turpentine to thin oil based polyurethane. Since the final mixture should be 3/4 poly and 1/4 solvent, you'll need to add eight cups of solvent to the mixing container.

Thinning polyurethane for spraying isn't completely necessary (unless you want a super smooth finish.) Thinned polyurethane will be able to lay down better, with less texture bumps. It will also dry to a buttery smooth finish.

Use a drop cloth or newspapers to protect surrounding areas from spray mist. Spray light mist coats, holding can 10-12 inches from surface. Move can with a smooth sweeping motion to avoid runs and sags. Several light coats give a better finish than one heavy coat.

Apply only one thin coat. Then, remove any dust nibs with 1,500-grit sandpaper or a piece of brown paper bag. Finally, using a soft cotton rag or polishing pad, buff the finish to a high shine using automotive paste wax, photo below, which has fine abrasives that polish the finish even further.

You can use mineral spirits, naptha, lacquer thinner... assuming that you have an oil base poly (not a waterborne). Naptha and mineral spirits are safer choices, but I often use lacquer thinner and even combinations of any of these products.

Water-based polyurethane requires at least two hours of dry time between coats, and you should only apply two coats in a day. It's important to remember that drying time is affected by temperature and humidity.

The thinner to use for oil-based varnish and polyurethane is mineral spirits – 3 or 4 parts varnish to 1 part mineral spirits. The ratio isn't crucial. If you prefer to apply these finishes with a rag, thin them with about 50% mineral spirits, essentially creating your own 'wiping varnish'.

The mineral spirits will provide a more forgiving coat of polyurethane and will also help any bubbles in the finish to burst before it sets up and dries. Pour the polyurethane into a separate container and add some mineral spirits. A good formula is three parts polyurethane to one part mineral spirits.

Do you sand after spraying polyurethane? ›

Sand Between Coats

Make sure to sand the polyurethane between coats. Sanding removes drips, bubbles and other uneven spots in each coat. Dry the first coat for a full 24 hours. If the coat feels tacky or sticky after that, let dry until it feels completely dry.

Wipe-ons form thinner coats than brush-ons, so use them when wear isn't a concern. Spray-on polys come in handy on hard-to reach surfaces, such as shutter louvers and chair spindles. Aerosol sprays require good technique to avoid drips, and extra prep time to protect surfaces from overspray.

Test Varathane Polyurethane in an inconspicuous area before beginning. Shake the can vigorously before and during use. Use a drop cloth or newspapers to protect surrounding areas from spray mist. Apply light mist coats, holding can 10-12” from the surface and spray with a smooth sweeping motion to avoid runs and sags.

Surfaces finished with oil-based polyurethanes can be used after around 4 days, but full cure normally takes 30 days. Even if the manufacturer's recommended time has passed, if you can still smell the polyurethane, it probably isn't dry. Fast-drying polyurethane is available in both water- and oil-based formulas.

After application, oil-based urethanes take about 24 hours to dry, while water-based urethanes require six hours of dry time. However, there's a significant difference between dry time and cure time. Cure time refers to the time needed before the wood floor is ready to be used.

Generally, a few coats are needed to achieve a smooth surface, as water-based polyurethane is thin; usually at least three coats will do the trick but sometimes as many as five coats will be necessary. One reason why water-based polyurethane is preferred over oil-based polyurethane is because it dries quicker.

Whenever water or any stain or finish that contains water comes in contact with wood, it causes the wood fibers to swell, which is called “grain raising” or “raised grain.” After the water has dried the wood feels rough to the touch, and thinly applied finishes also feel rough.

#1: Dust and Bubbles Will Get Trapped in Prior Coats

When applying polyurethane for the first time, bubbles are inevitable. Dust specks would appear if the bare wood wasn't cleaned properly before the polyurethane finish was applied or if all the sanding dust was blown onto the wooden surfaces.

Sounds like the poly might have picked up some dust. Try "sanding" its surface with a piece of kraft paper (for example, a piece of a brown paper bag), which is just abrasive enough to polish the surface.

1.3mm: 2-Pack top coats, enamels & polyurethanes.

How long does it take for 3 coats of polyurethane to cure? ›

Polyurethane dries in 24-48 hours and takes about 30 days to fully cure. Your new hardwood floor is installed, and just one more thing needs to be done to protect the wood and bring out that beautiful grain. It's time to apply the polyurethane varnish.

Standard thermoset polyurethanes can typically withstand temperatures between -80°F to 200°F. However, some polyurethane chemistries can have a higher tolerance to temperature, as high as 300°F. Outside of these temperatures, thermoset polyurethanes will tend to weaken or degrade over time.

Several substances can be used to thin polyurethane including turpentine, mineral spirits, paint thinner or, in some cases, water.

I use 220 grit. You sand polyurethane to (a) remove any dust bumps in the lower coat, and (b) cut the surface of the lower coat so that the upper coat has more surface area to bond to. You don't need the lower coat to be super-smooth because the upper coat will cover the roughness from sanding anyway.

Always use regular mineral spirits (Use mineral spirits if you are using oil-based polyurethane. Use water to dilute water-based polyurethane), not the odorless variety, to dilute the polyurethane; it has greater cutting power. To insure good adhesion, stay with the same brand of polyurethane.

Mineral spirits will not affect polyurethane, so a rejuvenator is needed for this. This is simply paint stripper thinned with solvent. It will soften the polyurethane so some of the top material can be wiped off.

To achieve the highest level of gloss, and to create the smoothest possible finish, wet sanding each coat of polyurethane is the preferred method. It is imperative that polyurethane be allowed to cure thoroughly before wet sanding to get the best results.

Polyurethane is so durable and water-resistant, it has largely replaced shellac and varnish as a wood finish. Originally, it had to be brushed on, but different formulations mean it can now be applied as a spray or by wiping it on with a rag.

What tool do you use to apply polyurethane? Oil based polyurethane can be applied with a natural bristle brush, foam brush, rag (if it's the wipe on type), or a spray on finish. Water based polyurethane can be applied with a synthetic bristle brush, foam brush, rag (if it's the wipe on type), or a spray on finish.

Can you sleep in house after polyurethane? ›

It's best to stay out of the house until the polyurethane is dry and the fumes have dissipated. Once it has dried, it is considered to be relatively safe and non-toxic. However, while it is still wet, it can release fumes that can be harmful to breathe.

The poly simply needs to cure for a while. Even after it "dries" and is safe to work on, the solvents that keep the polymers in suspension aren't all gone; they'll continue to evaporate, and the clear coat will fully harden in time. Check the can for your particular product; it should have a full cure time.

Set up a space heater in an adjoining doorway to keep the room temperature in the 70s F if you are drying the urethane in early to midspring or mid- to late autumn. Outside of the summer months, the need to ventilate might lower the temperature in the room below the optimum for drying urethane.

If you experience oil-based polyurethane not drying well, it's not likely that it's bad polyurethane. It's more likely that the wood you're finishing contains a natural oil or you have applied an oil to the wood and the oil hasn't dried.

Use a fan to direct fresh air over the area. It can take up to seven days for the urethane to be 90 percent cured and 30 days to be cured completely. However, you should need the fan only for the first day, with periodic use after to remove buildup of fumes.

Thinning polyurethane for spraying isn't completely necessary (unless you want a super smooth finish.) Thinned polyurethane will be able to lay down better, with less texture bumps. It will also dry to a buttery smooth finish.

The average coating thickness for urethane is 0.032” to 0.058”.

How to Apply Polyurethane: Brush On, Wipe On, or Spray? Every poly has its preferred applicator, typically a brush or cloth. Some polys also come in aerosol spray cans. Brush-on polys work best on flat surfaces where it's important to build up a durable film.

What is the best applicator for polyurethane on furniture? ›

Use a foam brush! It doesn't leave brush marks because it has no bristles. And it's easier to control the amount of polyurethane being applied. It's also easy to gently smooth out any line marks caused by the ends of the foam brush (if too much is applied) and the lines are easy to see and smooth out while applying.

Airless. As I mentioned above, you're better off spraying water based polyurethane with an airless sprayer — especially if you're tackling a big project. Water-based coating is more affected by temperature and tends to increase in viscosity the cooler it gets — a whole 10 percent for every 10-degree drop!

Applying three to four coats of oil-based polyurethane to a surface should create a strong and long lasting barrier. Even though oil-based polyurethane is thicker, you still have to apply multiple coats to ensure the entire surface is protected.

Even after sanding, fast-drying and most water-based polyurethanes will remain glossy, which won't help with adhesion. Finally, sanding polyurethane between coats is required for a perfect finish.

If the final coat of polyurethane dries with a smooth finish, sanding the entire surface is unnecessary. However, if you see the material with obvious signs of a rough finish, it's a step we don't recommend skipping.

Polyurethane is so durable and water-resistant, it has largely replaced shellac and varnish as a wood finish. Originally, it had to be brushed on, but different formulations mean it can now be applied as a spray or by wiping it on with a rag.

If you have larger bubbles that just won't pop with light sanding, you'll have to sand down all the polyurethane. This can be a time-consuming process, but it's the only way to get rid of all the bubbles. Once you've sanded down the surface, you'll start from scratch and apply new coats of polyurethane.