Although applying polyurethane to a hardwood floor can be a difficult and frustrating challenge if you're inexperienced with this product, with a set of good instructions and the right tools and materials, you should be able to successfully complete the process on your own.
The amount of polyurethane you'll need will depend on the surface area you want to cover. You'll find this coverage information on the product you choose.
Before applying your product, you'll need to prepare. Here are five things you should do.
1. Urethane Fumes
Get rid of them. This is critical. Use a window fan when applying the product and be sure to open as many windows as possible to get proper ventilation.
2. Floor Preparation
To avoid getting unwanted urethane on your baseboards, you will need to apply masking tape along the floor or just remove them while applying the coating.
Strip the floor of any old coating by sanding it with an orbital floor sander. If the floor is new you may need to scuff sand it before applying your product as well.
Vacuum all dust on the floor remaining from sanding and then clean the rest of the floor to remove any dirt or debris.
Wear an organic vapor respirator while in the room where the urethane is being applied—and even for a day or two afterward if you're going to spend extended time in the room.
5. Keeping the Extension Cord Off the Floor
When applying your product and using a fan it is important that you keep the fan's AC cord off the floor you are applying coating to. A good way to do this is to cut some split-flex tubing into short pieces and screw them into wall studs. Then insert the extension cord into the slit in the tubing.
Once you’ve finished preparations, it’s time to spread the coating on the floor.
Applying the Urethane
Apply the polyurethane with a lamb’s wool applicator. Start with a three-foot-wide strip, brushing with the grain and using a mop like a push broom to back-brush the urethane (back-brushing means to move the mop from the wet edge back into the wet finish). If you stab the brush into the finish and then move it, you'll see a mark where the brush landed. You might still see tiny—almost imperceptible—brush marks where your brush first touches and then is lifted from the floor. It is nearly impossible to apply urethane without leaving these unless you can find a way to brush completely across the room in one stroke. However, these tiny marks will rarely be noticed.
After each of the first three coats dries, scuff-sand the floor with 120-grit sandpaper on a pole sander. Clean any debris before continuing to the next coat, and then after the fourth and final coat, allow the urethane to dry completely. Typically, depending on the temperature and humidity, it takes about 72 hours for the urethane to fully cure.
When you’re finished, if you’ve followed these rules, you should have a nice looking finish that will protect the floor from moisture and from becoming dull.