Lambswool Applicators The method recommended for applying oil-based polyurethane to hardwood floors is with the use of a lambswool applicator on a wooden block. One word of caution with lambswool applicators: The fibers of these applicators have a tendency to get stuck in wet finish.
It depends on what type of poly you are putting down. Oil based polyurethane I use a lamswool applicator on a wood pad and foam brushes. I use the same wood block with a special foam pad. I use 16--18 inch pads on my floors and mostly the water-borne polys like Bona . Do not try the T-Bar applicator.
For the best results, apply thin, even coats of polyurethane. Multiple thin coats are preferable to one thick coat, as they reduce the risk of drips and bubbles. Use a high-quality floor finish applicator, such as a brush or roller designed specifically for floor finishes, to achieve an even coat.
But when it comes to applying a smooth coat of clear finish, such as polyurethane, a foam brush is not my first choice. Instead of bristles, it has a blade. The blunt sides leave two parallel ridges of finish, like a snowplow on the highway. Also, the foam head contains air, which can leave bubbles in your finish.
Oil based polyurethane I use a lamswool applicator on a wood pad and foam brushes.
Prepare the polyurethane by reducing it about 10 percent with mineral spirits, unless you're using water-based polyurethane, which doesn't need thinning. Thinning the polyurethane makes it flow on more smoothly and reduces brush marks. Quick Tip!
Wetting your brush before applying polyurethane is not necessary and can actually hinder the application process. Instead, ensure your brush is clean and dry before dipping it into the polyurethane.
Two coats of finish are suggested for most interior projects. When sealing floors, you should apply three coats. However, do not apply more than two coats in one day. 220 grit sandpaper should be used between coats to remove any air bubbles, but avoid using steel wool.
I prefer to use a wipe-on poly because it goes on thinner and does not leave the brush marks. You could sand what you have to smooth it, then thin the poly about 50% and use it as a wipe-on. Using it as a wipe-on applies it in a thinner layer and with it thinner it will also dry faster.
Waterborne polyurethanes usually require a minimum of 3-4 coats to be effective. Although there is some evidence that too many coats can result in a plastic-like finish, waterborne polyesters are thinner than other types and therefore require several more coats to provide the same protection for hardwood floors.
Contrary to popular belief, no further buffing is necessary after the finish dries. Polyurethane dries to a pre-determined level of shine (the can will tell you whether it's satin or semi-gloss). Its luster will be dulled by any further buffing or polishing.
Instructions for Applying Your Polyurethane Finish
Remember to always work in the direction of the wood grain on the second and third coats. Abrade the finish/floor in between coats, but do not buff the final coat! Usually you'll need about 3-4 coats to fully protect the floor, one or two seals, and two finish coats.
Lambswool Applicators
The method recommended for applying oil-based polyurethane to hardwood floors is with the use of a lambswool applicator on a wooden block. One word of caution with lambswool applicators: The fibers of these applicators have a tendency to get stuck in wet finish.
Make sure to sand the polyurethane between coats.
You should use an automotive polishing compound and a buffer for big areas. Small areas will have to be polished by hand unless you have some funky buffing tools. Make sure the poly has cured for a minimum of 4-5 days at 70f. Do not try to polish an uncured film.
Polyurethane will dry to touch in 3 hours. Under ideal drying conditions, allow 6 hours before recoating. Overnight drying is recommended.
Thin your polyurethane with mineral spirits.
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.
If your existing urethane finish needs extra protection but not a total refinishing, you can re-coat it with Minwax® Helmsman® Spar Urethane, provided you follow the three rules for re-coating: clean, dry and scuff.
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.
Lambswool applicators
A lambswool applicator on a wood block is the recommended method for applying oil-based polyurethane to a hardwood floor. But if you've recently bought a lambswool applicator, be careful. The fibers tend to get stuck in wet finish.
When applying polyurethane use a soft foam brush not a bristle brush which should eliminate bubbles. It is highly recommended to use very fine steel wool to smooth the surface between coats and that will also remove any small air bubbles providing a glass like finish.