Streaks and brush marks can be fixed by sanding and reapplying. Let the coat with streaks or brush strokes dry completely. Next, lightly sand with 220 grit sandpaper to remove the streaks or brush strokes. Then, remove the sanding dust.
*How Do I Remove Brush Strokes from the 3rd Coat of High Performance Polyurethane? Sand down the final finish with a 220-grit foam sanding pad, and then add another layer of General Finishes High Performance PolyurethaneTopcoat. Apply liberally than you did previously without heavy back-brushing.
Sand: If wiping doesn't resolve the issue, lightly sand with 220-grit sandpaper and apply a fresh coat of polyurethane. Improper sanding between coats can result in uneven gloss, so ensure each layer is sanded smoothly before reapplication.
Just sand that smooth after it dries and repeat a couple times to build up a nice thick coat. After you have a few layers thick, sand it smooth one more time and make your own wipe on poly (50:50 - mineral spirits:poly) and wipe it on.
Wet-sanding is a technique that can be used to create a buttery smooth finish on painted surfaces unlike anything else. It is a less abrasive method to remove dust nibs, orange peel texture, brush strokes, and other surface imperfections from paint.
Additives like water or linseed oil can help smooth out your paint and prevent brush marks. If you don't have additives on hand, try using a roller instead!
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. Sand the topcoat with 180 to 220 grit sandpaper.
Sand it with 220 on a foam block, vacuum off, sand with 400, vacuum, 0000 steel wool, vacuum, tack rag, and apply your final coat with a wide foam brush. Before my "final coat", even if my previous coat was perfect, I sand with 400-600 and 0000 steel wool to make it silky smooth before that last coat.
You can rub out all types of film forming finishes, including shellac, lacquer, oil based varnish and polyurethane, waterbased coatings and catalyzed or conversion coatings.
Brush on a coat of varnish; hold the brush at a right angle 10° to the surface; and, working in the direction of the grain, lightly skim the varnish with the bristle tips to help level it.
The streaking you are describing seems to be the result of the finish being applied too thin. But you don't want to go quite as thick as a brushed-on coat. The way I get a coat that is “just right”, is by using the wipe on/no wipe off method. And I would abandon the sponge applicator in favor of a simple folded rag.
Polyurethane can help make your wood surfaces look smooth and glassy, but it may feel a bit bumpy or uneven at first. To create a completely polished surface, it may be worth it to sand the surface of your wood. Buff the surface with car polish for a shiny finish or use paste wax for a satin finish.
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.
Coarse-grit sandpaper (around 60-80 grit) is ideal for the initial sanding phase. It effectively removes the bulk of the polyurethane. Use a floor sander or a hand-held orbital sander for larger surfaces to ensure even coverage. A sanding block or detail sander may be necessary for edges and corners.
An oil-based Polyurethane is going to take 24 hours before being ready for sanding or touching. Type of Wood: Aromatic cedars and Rosewood may result in drying and curing delays because their natural oils slow the process.
Simply just give your polyurethane finish a good buffing with a new 180 or 220 grit screen. This will remove flaws such as brush marks, lap marks, bubbles, raised grain and any particles left on the polyurethane finish. Uneven sheen and coatings are simply fixed by stirring more and applying a more even second coat.
Minwax® PolyShades® is an easy way to change the color of your currently stained or polyurethane finished wood. There's no stripping or heavy sanding necessary to remove the old finish!
Use a Paint Additive
You can use a product like Floetrol, which is an additive for latex paint that helps eliminate brush strokes and extend the paint's drying time.
Tip: If the trim is new or already smooth, lightly sand using 120-grit sandpaper until all shine disappears from the trim. If the trim is rough and worn, start by sanding with coarse, 80-grit sandpaper. Then, move to less-coarse sandpaper such as 100- or 120-grit to smooth the surface.