How Much Paint You Really Need
How much paint you will need to satisfactorily complete a paint project is determined by 2 factors. The first, paint coverage, is a familiar concept to most people. It simply concerns the square footage of surface area to be painted, and “paint coverage calculators” abound on the web. However, the second concept, paint color coverage, has a much more pronounced effect on how much paint will be needed and the cost of paint projects. Unfortunately, paint color coverage is a novel concept to many painters and, in fact, is poorly understood even by many professionals. Knowing the secrets of paint color coverage will allow you to reduce the number coats you have to apply and minimize how much paint you have to buy.
Paint color coverage refers to the fact that new coats of paint are always affected by the pre-existing colors on the surface before the fresh coats are applied. This fact is unavoidable, but there are a few tricks that will help you overcome this problem and may save you hundreds on your next paint project. These money-saving secrets relate to how you use your primer.
Reasons to Use Primer with Paint
Primer plays 2 important roles in painting projects. Firstly, if you are painting a wall that has never been painted (with water-based paint) before, primer will allow your new paint to stick (or “mechanically bond”) to the surface. Since primer is typically not necessary if the wall has previously been painted, many people skip this step. Unfortunately, doing so negates its 2nd (often, more valuable) role in color coverage.
There are 2 methods for using primer to aid in color coverage. In the first case, when applying light color paint to a darker wall color, you can maximize your color coverage by applying a white primer coat before applying your new paint. In the second case, when Painting dark color paint onto a lighter wall color, maximize your color coverage by having your primer “tinted” the same color as your new paint. Many people are surprised to learn that this is possible. But the fact is, your local paint retailer will happily add any color they carry to any primer you want (thereby “tinting” it) for free!
Use Plain White Primer for Light Paint Colors
In our first case, if you decide to paint a wall in your house with a light yellow color, but the wall is currently a deep dark brown, you will go through bucket after bucket of paint trying to cover that brown, easily doing 4 – 6 coats or more. But if you put down a coat of white primer first, you could be done after 2 coats of paint.
The reasoning here is simple. Every color in the visible spectrum can be assigned a number based on a luminosity scale (a scale from light to dark) from 0 to 9 where white is 0 and black is 9. Now suppose that the brown you are trying to cover has a score of 8, and the yellow paint you want to apply has a 4.
When you apply a coat of paint to a wall, it doesn’t fully cover the surface, so the new paint color essentially mixes with the color of the wall. Suppose that mixing these 2 colors produces a new color that is essentially the average of the first 2, so the first coat of yellow over the brown will give you a color with a luminosity score of 6 (8+4=12, 12/2=6). After that dries, adding another coat of yellow (score of 4) brings the color on the wall to a score of 5.
Like this, it will actually take quite a while to reach a number that is close enough to the yellow color you’ve chosen that you can’t tell any difference (and mathematically, you will never actually reach an average of 4!)
However, if you put a coat of pure white primer (which has a score of 0) on top of the brown color wall first, this immediately brings your luminosity score down to 4 (8 + 0 = 8/2 = 4, the average). This means you may only need one coat of yellow paint to give you the right hue and saturation. In reality of course, you will always want to do at least 2 coats. But even with a total of 3 coats (primer and paint) you are way ahead of the paint-only option.