Patchy paint can result if paint has been applied unevenly. Patchy paint can be down to a variation in surface absorption. Walls might appear patchy if they have variation in texture. Using paint that is not fully mixed can cause a patchy appearance.
You need to paint the whole wall. Prime the patch. Let dry. Sand the primer. Paint the patch. Let dry. Sand the whole wall. Cut and roll just that wall and paint the whole wall. Best results.
Patchiness in a painted wall can happen due to several factors, such as applying too thin a coat of paint, uneven surface texture, or not allowing each coat to dry properly before applying the next. Make sure to use quality paint and apply multiple thin layers for better coverage. For more, check out my Quora Profile.
Having paint streak is very common when not applying enough material, or using tools that don't hold enough material to disperse it properly. You want to make sure the roller has a uniform amount of paint on it while rolling, if it starts ``screaming'' at you on the wall, there's not enough paint left on the roller.
So you have two choices - either sand the whole wall smooth and repaint all of it or get a mini roller and put a few coats of paint on the patches with that which should build a bit of texture and might help. To be honest though, starting with it all flat would be the only way to lose those patches completely.
Don't worry if the wall looks patchy at first – this is normal for claypaint. Wait a few hours and you will notice that the colour evens out as it dries (dark colours take much longer to settle to their final colour). We advise that you wait until the colour has settled before applying subsequent coats.
When newly applied latex paint is exposed to high moisture or humidity while it's drying and/or curing, the surfactants can rise prematurely to the film's surface, producing a residue or splotches. This residue can be sticky, discolored, glossy or soapy in appearance.
Unfortunately, roller marks will probably not go away when the paint dries out. However, as the paint dries some of the roller marks will become slightly less noticeable. But simply waiting until the paint has dried won't solve the problem completely.
Maintain a Wet Edge: To avoid paint streaks and overlap marks, always maintain a wet edge by painting over a section before it dries completely.
Brush marks are caused by strokes that leave the paint with a rough texture and visible brush strokes. The rough texture and visible brush strokes can be easily covered in a second coat of paint by using a slightly different technique than you used for your first coat.
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.
Not Fully Loading the Roller
The roller needs to be fully loaded with paint to the core, otherwise you'll get air bubbles on your wall, resulting in “paint acne.” To avoid this mistake, roll back and forth on the roller tray until all bubbles are gone and the roller feels heavy.
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.
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.
Lightly sand the troublesome area with 150-grit sandpaper, then tack the walls. That's painter lingo for “Wipe it with a cloth to get rid of dust.” (Easier than the lingo makes it sound!) Then re-paint the area, maintaining a wet edge—meaning, don't let the paint dry until you finish the wall.
Ceilings and Drywall - Medium 3/8″ roller covers work best. Walls, Wood, and Metal - Small 1/4″ roller covers or foam rollers will produce the smoothest finish. Light to Medium Textured Surfaces - Microfiber rollers are best. Smooth Surfaces - Use a white woven short nap roller for an ultra fine finish.
You want to use even, consistent pressure when painting. Remember, pressing too hard will leave behind roller-edge streaks. Not pressing hard enough will lead to inconsistent paint coverage. Practice on a loose piece of drywall to get the feel down before painting your wall.
If they are due to improper painting techniques or using low-quality tools, they may not go away completely even after the paint dries. However, if the streaks are caused by a lack of thorough drying between coats or high humidity levels, they may disappear once the paint has fully dried.
Roll a “W” on the wall with the roller, filling the empty spaces in a top to bottom motion. This will help place an even distribution of paint onto the wall. Repeat this until you have completely covered the entire wall.
Re-fill often or if you find yourself applying force to extract paint from the roller. You shouldn't need more than 2 coats of paint to cover the old color unless it's very dark. To cover the sheen problem in your photo's one good coat with a paint and primer should suffice.
Before you start a paint job, you actually want to wet the paint roller cover with water. “This primes the roller cover to soak up as much paint as possible,” Barr explains. But don't go too crazy—Barr suggests removing excess moisture with a paper towel and a good shake of the roller so it's just slightly damp.
The first is that the roller was not loaded enough with paint. When this happens, the roller drags across the surface, leaving streaks behind. Another reason for roller marks is when the paint is too thick. In this case, the roller cannot apply the paint evenly to the surface, which results in streaks.
The larger patches show through because of differences in the texture of the surrounding wall, which has had several coats of paint applied over the years. So you have roller texture and smooth drywall patches.
Ghosting is when damp air and particulates like soot and dust condense on a wall or ceiling in streaks or lines. Ghosting can result from poor ventilation, improper insulation, humidity, and a high concentration of particulates in the air.
You can identify paint chalking by the look of chalky wall paint on the building surfaces. It is a paint defect that occurs on the surface when the paint film degrades over time from a painted object or building and gradually breaks down, leaving a powdery residue on the surface.