An uneven finish can result from applying polyurethane too thickly, failing to stir it properly, or working in extreme temperatures. To correct blotchiness: Sand the entire surface lightly to even it out.
Another way to get it nice an smooth is to do a rubbed finish. Instead of applying with a brush, use a rag or wool applicator. This will allow you to do multiple things coats and get a nice smooth finish. You can also use the silicone oil with this with the same caveat.
To fix it grab a hard block with some 220 and do a directional sand until you get the surface even. And be very careful as you approach the edges, as there tendency to thin them more than the surrounding surface. Then clean with compressed air and a damp rag (mineral spirits). Apply another coat with thinned out poly.
Use a damp rag or sealant tool to smooth the bead of sealant and seal the seam. Clean up immediately with a damp rag.
Use Masking Tape
Before applying the silicone, use some tape to keep the sealant from smearing and to help you achieve straight lines. As you lay the masking tape, allow enough space for the sealant and ensure it is straight so that it leaves behind sharp lines when removed.
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.
“The most common causes for bubbles are shaking the can and improper brush prep—you don't stick a brush into the finish without first soaking the bristles in mineral spirits, for oil-based polys, or in water, for water-based polys.
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.
In short, that rough texture that you feel is basically a mix of micro-level dirt that has stuck to your clear coat that won't come off with a simple wash. It can be things like industrial fallout, paint overspray, metal shavings, dust, etc…
Bubbles and streaks can ruin the smooth finish of your polyurethane floor. To avoid bubbles, make sure to stir the polyurethane gently and avoid shaking the can. When applying, use a high-quality brush or roller and apply thin, even coats.
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. Wipe off any residue after sanding.
Use a Roller on Large, Flat Surfaces
rollers lets you apply the poly fast and evenly. No brushstrokes, puddles or thin spots.
Start sanding with coarse-grit sandpaper. It will strip away the top layers of polyurethane. Work methodically in the direction of the wood grain to avoid scratches. Once the majority of the finish is removed, switch to medium-grit sandpaper.
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.
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!
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.
*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.
Urethane can be stored for a long time as long as its kept dry and sealed tightly. You will know that its been contaminated or moisture got in if, when you open it, it looks like cottage cheese.
Paint Bubbling on Car Hood & Panels
As the moisture is painted over, air is then trapped within and will form bubbles underneath the paint. Over time these tiny bubbles will come up to the surface and cause the paint to chip off. To repair this problem the only answer is to refinish the panel.
Polyurethane will dry to touch in 3 hours. Under ideal drying conditions, allow 6 hours before recoating. Overnight drying is recommended.
Too thick of a coat: Applying too thick of a coat can extend drying times, leading to issues with subsequent layers.
Two coats of oil based Polyurethane are recommended on stairs. For added step protection and slip-resistance, opt for three coats, while water based polyurethane, you can apply four or more coats. Wait for at least 8 hours before reapplying oil-based Polyurethane and 2 hours for water-based polyurethane.