Use of the wrong type or size of brush. Applying too thin of a paint film. Painting a hot surface or in direct sunlight. Coating a very porous surface.
The best way to limit the appearance of brush lines is to use a brush around the edges and a foam roller for the rest along with a good latex extender like floetrol. The finish paint you're using matters too, not all paint is created equal. Some have great self leveling properties and some dont.
As others said this is the result of too much paint and bad quality brush. For oil based paints use a natural bristle brush. You'll always have brush marks when brushing but a high quality paint and brush will level off so they're hardly noticeable.
Start a fresh line 1/2 a roller width away from the paint. Roll out and work it back towards the rest of the paint. This can help cut down on the excess paint that's creating the lines. Or start in the paint and move out into the unpainted area, then dry roll everything you just painted, to pick up any excess.
Why it happens: An excessive amount of paint on your roller or paintbrush can cause paint to drip and run. Streaks, where paint is unevenly distributed on a wall, typically result from having too little paint on your roller or brush.
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.
Dust, dirt, or oils can prevent paint from adhering correctly, leading to uneven paint streaks. Apply a quality primer to create a smooth, uniform surface that paint can adhere to effectively.
Or, you can use additives like Floetrol or Penetrol to extend the open time without sacrificing durability. Meaning, these additives specifically help with greatly reducing the brush and roller marks.
You want to glide the brush on its edge at a 45-degree angle in a slight arc motion, ensuring you are getting into the tight areas. The slower you spread the paint, the more concise the brush line will be. Make sure you cut in on every coat of paint that is applied.
Soft Nylon & Polyester—Use this type of bristle for all paints, especially semi-gloss and satin finishes. They provide extra flex for smooth application, leave few brush marks, and have an excellent paint capacity.
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.
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.
The Staalmeester Ultimate ONE synthetic brushes will change how you see paintbrushes and it is absolutely the best paint brush for no brush strokes! The blending and quality make of this brush is so good that Jennylyn could not stop raving about it when we got them in stock for the first time.
Cut Lines: Satin paint is also easier to fix than flat paint because the glossier finish helps to hide brush strokes and other flaws.
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.
What Causes Brush and Roller Marks? Application of additional paint, or re-brushing or re-rolling, in areas where the paint has partially dried. "Working" paint too much during application (e.g., applying too quickly or for too long). Use of the wrong type or nap size of roller cover.
More often than not, roller marks occur when you fail to load your roller with enough paint, or have exhausted the paint in your roller and are trying to cover more area than you should. Finally, applying the wrong amount of pressure can cause paint to push out around the edge of the roller, creating a streak.
Also, a second coat of paint helps remove roller marks by allowing you to feather out some of the unevenness in the finish. You can do this by overlapping the uneven areas to create a more uniform finish. However, you need to apply the paints with the proper technique for this to work.
Begin by loading the roller with paint, then rolling it across the ridges of the tray to remove excess. Starting at one end of the wall, hold the roller at a slight angle and apply light pressure as you roll it across the surface. Move quickly to avoid leaving streaks, and overlap each stroke slightly.
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.
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.