Most ready-to-use paints are created for certain average conditions that are generally not there on the day you choose to paint. The result of that is that the paint doesn’t flow well to leave a smooth finish and you end up with ugly roller marks or brush marks or scratches or overlap marks.
The paint is broadly made for what would be an average room temperature or outside temperature for the market where those paints are sold. The problem is, as long as there is a temperature drift, either up or down, the paint will be more difficult to brush or roll on the wall. Water-based interior paints, Emulsions or Latex tend to dry too quickly when the temperature is warmer than average, and the result of this is that each new painted section can be streaked because the previous piece has dried too quickly. .
Painters / decorators describe this phenomenon as “losing the wet edge.” Painting ceilings can be especially problematic because all the hot air in the room rises to the ceiling, compounding the problem of drying too quickly. If you are applying water based paint / masonry paint to plastered or similar exterior walls and the weather is dry or dry with a breeze or worse, if the sun is shining directly on that wall while you are painting … you will have a job. really tough because those weather conditions mean you’ll lose that “wet edge” almost as soon as you apply a roller full of paint.
It is best to choose a day that is neither too hot nor too cold to paint the exterior walls, etc. If you are applying oil-based paints or varnishes, especially outdoors on a good day, you will notice that the paint becomes very heavy and the brush will tend to drag, making the painting process much more tedious. The reason for this is that the solvent in the paint evaporates quickly in warmer conditions and the paint will need to be thinned a bit to make application easier.
In order for paint or varnish to flow, historically a little water is added to water-based paints and some alcohol to oil-based paints. That generally makes the paint flow better. However, there are some negative consequences to diluting the paint in this way, for example … the paint loses some of its ‘hiding power’, which can be a nuisance when using ‘weak hiding’ color paints ( yellows, reds etc) because you probably need to apply additional coats to get a finish and lock out previous colors etc.
With glitter and other oil-based paints, etc., diluting in this way will make it flow better but will remove the hiding power and will lose a lot of shine after a while. Another alternative would be to use a paint additive that is made to make the paint flow and cover better in less than ideal conditions, etc. You can get paint additives (sometimes called paint conditioners) for emulsion and oil-based paints at most of the best paint stores. The water-based additive (conditioner) is ideal for any paint color, but will not be suitable for water-based varnishes due to its milky appearance. However, it does not change the color or finish, etc.
Water-based paint additives are designed to keep the wet edge open and generally allow you to get a finish without brush marks or streaks. In fact, some water-based paint additives help to hide power in a spectacular way, especially in weak colors like reds, yellows, etc., where you can save a few coats and a lot of hard work. Oil-based paint additives will work well in any oil-based paint and varnish. Check your paint to see if the cleaning is with white spirit, etc. and if so, it means it is oil based and suitable for that paint.