Watered-down paint also causes inconsistencies, especially when the water and paint are poorly mixed. Finally, watered-down paint is less UV-resistant, adheres poorly, is more prone to chalking, and—just generally speaking—isn't going to last as long as the manufacturer intended.
On new plaster, the first coat needs to penetrate the surface to bond. If the first coat is not watered down it will almost certainly be too thick to do this, so will not penetrate and just lay on the surface, which is a dusty surface. In time the paint will peel off leaving a horrible mess.
You can and often should dilute for best results. You dont want to slap the paint on in one go but go in layers. Thinning helps you do that.
A little will make it flow on easier. But the more water you add to the paint, the thinner the coat will be, until it becomes a watercolor paint. It's durability will be watered down too.
It is always best to NOT ADD any water to the factory chemical mix of the paint product. Adding water affects the drying time, and the physical properties of the paint coating , and its ability to adhere to whatever you hope to successfully paint. Do not try to thin down any paint. Bad idea.
When a painting contractor waters down paint, they are typically adding a significant amount of water to it. Think two gallons of water for every five gallons of paint. In contrast, the process of thinning paint involves a relatively small amount of water: 2-4 cups for every five gallons of paint.
Sheen: The more water you add, the more matte the paint will become, regardless of what sheen or line of paint you start with.
If you water down paint too much then you will apply thinner coats, and it won't have the same covering power. You will need to apply additional coats.
So watering down your first coat as a 'mist coat' will help the plaster to soak up the paint and create a bond between the new plaster and the paint.
Yes, paint can indeed be too thick, and this can lead to several issues during both the application process and the drying period. We always suggest water thinning most of our water based paints by 10% or so, it usually always helps!
To thin down emulsion ready for spraying, the best ratio is 70/30. That is 70% of paint and 30% water. Some painters prefer an 80/20 ratio, but this greatly depends on the paint you are using and how thick it was, to begin with.
The bottom line is that watery paint is unusable. So if your paint is too watery and you attempt to use it to paint your home, you will notice that the paint won't adhere to surface correctly. It will be 'thin' and therefore will perform poorer than expected.
Check the thickness by running the paint through a funnel. If it flows freely through the funnel, you know the paint is thinned enough. If the paint is too thick, add an additional ⅛ cup of water (30 milliliters) per gallon (3.8 liters) of water and mix.
Oil-based paints should be thinned or cleaned up only with petroleum or mineral-based products. In contrast, latex paint is water-based and should be cleaned up and thinned only with water.
Note: without water, the color will be more opaque and cover the previous layer of paint. Note that colors will darken as they dry, particularly if they are diluted with a lot of water. Do not lighten colors with white: it dulls the shade.
Too Much Water
You don't want to be too thin, but a mist coat needs to be thin—almost like a soup. The water will not seep into the substrate if the mist coat is too watery.
However, getting this look through watering down paint is a big no, no. The biggest issue we find when watering down paints is, how the water effects the quality of the paint. Once water has been added to an opaque paint the adhesion, durability and colour consistency will all be effected.
Why Mist Coat? We always recommend applying a mist coat because skipping this step can lead to quite disastrous consequences. For example, painting directly onto plaster can cause paint to flake, crack and more.
Ensure you leave at least 2 hours between coats. To be safe, for best results leave 4 hours.
Some painters can dilute wall paint (but not to make it spread over a larger space or for economy), but because sometimes the wall surface requires a less thick application - but perhaps more coats).
If you are using a roller, the paint may need to be thinned slightly to make it easier to apply and to achieve a smoother finish. If you're using a sprayer, however, it's almost essential to thin the paint, as most equipment requires a more liquid consistency to work properly.
For good access to the paint we suggest you pour your paint into a larger container, a paint kettle is a good choice for a small volume 1L-2.5L or a scuttle bucket (roller bucket) is a better option for larger volumes of 2.5L-10L (when you're painting a whole room).
Remove any loose dust with the dry brush or vacuum cleaner, then wet the surface using a damp cloth – this helps water-based paint adhere to the surface and minimises brush marks. Apply your paint in quick, smooth strokes, taking care not to overload the brush.
For Rolling
Follow the same thinning instructions for brushing and rolling. Adding Floetrol when rolling can minimize lap lines. However, Otto doesn't recommend thinning with water when applying latex paint with a roller. “It doesn't give the look the manufacturer intends and can leave streaks,” she says.
You'll find a few different ratios of water-to-paint floating around online when it comes to your mist coat. However, a common ratio is 3:1 – 3 parts paint to 1 part water. Having said that, before you mix up your mist coat, make sure to read the information on the back of your paint tin.