With water – based topcoats, sand any “grain-raise” smooth before applying the final coat . Note: Sanding between coats is not necessary, but it will provide a better finish. After a coat has dried, use 220 or 240 grit sandpaper or extra fine steel wool to lightly sand surface.
How to use water based polyurethane without brush marks ! Sand your surface in successively finer grits down to 220 grit with a random orbital sander. Spray the surface with water and allow it to dry. Sand your surface to 220 grit with a random orbital sander, to remove the raised grain. Open the can of water based polyurethane .
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.
Failing to sand between coats of polyurethane does not have a significant impact on the finish. Even so, I still advise that you sand between the coats when applying polyurethane as this will help increase the adhesion between the layers to give you a more level finish.
Generally, more than 3 coats of poly doesn’t do much good. It’s really not needed nor recommended. Each additional coat needs to be buffed so you are kind of buffing off half of the previous layer. It’s kind of like nail polish where it takes longer and longer to dry and cure for each coat .
It roughs up the surface just enough to give it a bit of grip. Multiple coats is the same as anything else. Multiple coats makes the coating thicker, stronger and more lustrous.
Apply polyurethane using a bristle or foam brush about 2″ wide. Foam works well and eliminates the chore of cleaning, because the brushes are cheap and thus disposable. Brush the polyurethane just like brushing paint. If there are bubbles, brush back over the finish lightly to make them pop out.
A roller is the recommended method for applying some water – based polyurethanes, as well as some oil- based polyurethanes and moisture-cured poly finishes. Rollers are good for finishing multi-direction floors, like parquets.
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 .
A 6-in. rollers lets you apply the poly fast and evenly. No brushstrokes, puddles or thin spots.
Hand Rub With Wipe-On Varnish or Oil If you want to transform the sheen from high gloss to satin or matte, then using a hardening oil such as tung oil is a good way to do it. Apply a base coat of gloss water- or oil-based polyurethane , let it dry and scuff it with 220-grit wet/dry sandpaper. Apply a second coat.
If unable to do so, wait a minimum of 72 hours, then lightly sand and recoat. Apply at least three coats on unfinished wood and two coats on surfaces already finished. After final coat, allow 24 hours before normal use.