Your surface was not clean when you started. You may have used a degreaser to clean the surface, vinegar or another cleaner, but did you get every spec of dust off? Dust is usually the culprit. Be sure to use a barely damp microfiber cloth and wipe your piece down thoroughly.
Scrape off the offending bits, then use your 150-grit sandpaper to smooth the wall. Tack it and paint again. If you can't get a big blister smooth, you may have to spackle the wall, let it dry, and then sand it smooth, he says. “Then tack and try again.”
This is perfectly common when spraying on primer. It's easily corrected by sanding with a fine-grit paper before the finish paint is applied; or it can be prevented by backrolling as the paint is sprayed. In this case, neither action was taken, and a low-sheen finish paint was applied.
It can be things like industrial fallout, paint overspray, metal shavings, dust, etc…
Old paint might have debris or clumps (even if it's an unopened can!) and new paint might need to be stirred.
If you want your paint to have a smooth finish, the technique you use is very important. Keep your brush at a 90-degree angle while applying the paint and feather as you go. Between coats, sand the wall lightly using a very high grit sand sponge of at least 220 grit.
High humidity levels can cause the paint to dry too slowly, trapping air and moisture, which results in a rough texture. Extreme temperatures can also affect the drying process; if the paint dries too quickly, it might leave an uneven finish.
Clear coat needs to "flow", which requires a full wet coat, which is applied with 50% overlapping strokes, with a little closer application of the nozzle, and sometimes with slower speed than you spray the paint. The trick is not to over coat it and get runs or sags.
Applying the second coat too early will result in lost time, money, and effort. Not only that but it'll also create additional stress that's not necessary. Applying the second coat too early will result in streaks, peeling paint, and uneven color.
Application
If your roller runs dry, you'll find yourself with uneven patches, leaving your walls looking inconsistent. Also resist the urge to rework wet paint and trust the process… it will look patchy whilst drying! Another common culprit in achieving a patchy effect is not maintaining a wet edge whist cutting in.
Why it happens: Uneven or blotchy paint occurs when you've either skipped priming or not adequately primed your wall before painting. This can also result from not applying enough coats of paint to get a uniform finish.
Uneven pressure is the most common cause of roller marks and noticeable edge marks. But cheap, poor-quality rollers can also cause roller marks. Sand away any raised marks, clean off the dust, then use a high-quality roller and apply a fresh coat of paint with even pressure.
Wall textures have been commonly used to finish interior walls surfaces and to hide imperfections in the drywall. In many cases, this was likely done as a cost-saving option.
You did not sand in between coats of paint. Not only is it important to sand between primer coats, but also between coats of paint and especially between coats of topcoat. If you have primed your piece, each coat is less rough, but I always do a quick sanding just to be sure.
If you want a really smooth finish, you can wet sand the first coat and remove all the stipples before putting on a 2nd coat, but that's a lot of work. Or you can thin down your 2nd coat so it won't go on too thick.
Use a fine grit (a 220 grit sanding sponge works great) and just go over everything quickly. You don't want to sand the paint off, you just want to smooth it out a bit before applying another coat. Believe it or not, I get this question fairly often so let me just be clear: do not sand your final coat.
Weathered Surfaces: If the existing paint is weathered, faded, or peeling, applying two coats is generally recommended to ensure proper coverage, adhesion, and protection against moisture and UV damage.
Humidity while painting: Humidity plays a role in causing orange peel paint texture. High levels of humidity can make your paint take more time to dry. In low humidity, the paint may dry too quickly. Both of these scenarios are likely to cause orange peel.
Eggshell finish, perennially popular with professional and DIY painters alike, has a low-sheen reminiscent of flat or matte, but it is infinitely more durable than its namesake.
Don't Overwork the Paint.
If you go back and forth over the paint, brushstrokes will almost certainly occur. Rather, THINK THIN. Instead of using globs of paint, apply multiple thin coats. Also, brushing (or rolling) from one end to the other of your piece will avoid starting and stopping strokes.
The clear coat is a type of paint that is pretty durable and resistant to scratching. It's most often used on cars since it can withstand any weather conditions. However, it also has other benefits. For example, it provides a smooth finish so your car looks shiny.