A paint and primer in one is not designed for every project. Some surfaces require specialty primers that block out color, have higher adhesion qualities or handle corroded surfaces. Exterior surfaces such as wood and metal require a primer for proper adhesion and blocking power.
If your drywall has been painted before, it is possible to get away with using a paint with a primer added to it. This will work best if you are keeping a similar paint sheen and color to what is already on the walls. If you're making a big change in color though, play it safe by applying a separate primer.
If the surface you are about to paint is previously painted (previously prepared), and you are going to re-paint with a similar color and sheen of paint, then you may use a paint and primer in one product. In most situations, paint professionals would recommend that you use a quality primer before painting.
Typically, contractors use a primer, then two coats of paint—the primer to seal the surface and improve paint adhesion and the paint to provide color and protection.
Adhering to surfaces better than regular paints but not as well as primers, 2 in 1 paint and primer products work best on surfaces that have already been painted. When used on raw surfaces, previously applying a high-quality primer can help ensure better coating adhesion.
In most situations, a good rule of thumb is to use a primer plus two coats of paint. If you use this rule, you may do one more coat than needed but this won't hurt the final product.
A thickness of up to 50 microns is possible through one coat of primer and paint. To obtain a greater thickness an additional coat of paint, rather than primer, may be applied after almost curing the first coat.
Two coats of paint ALWAYS looks better and more professional than just one. The best paints sold by top paint vendors recommend a two coat system.
HOW LONG DOES IT TAKE FOR PRIMER TO DRY? Most latex primers dry to the touch in 30 minutes to one hour. But for best results, don't paint until the primer completely dries—which can take up to 3 hours, depending on temperature and humidity. Once the primer is completely dry, it's prime time for painting.
A good rule of thumb is to wait at least three hours to recoat your paint or primer if it's water-based. Waiting 24 hours is best for oil-based paint and primer. If you're unsure, the instructions on the paint's label can give you the best final say.
Multiple coats required when: 1) Painting over uncoated, porous, heavily textured or repaired exterior surfaces. 2) Over woods that contain tannins such as redwood or cedar. 3) Applying over heavy stains, which may require spot priming, multiple coats, and/or longer dry time.
In general, the only time a primer is not needed is if you're re-painting a surface that's in good condition. Your neighborhood Sherwin-Williams paint expert can provide additional advice about selecting and applying the right primer for your project.
You probably don't need a primer. If the current wall is smooth, clean and covered with the same type of paint (both are oil-based for example), you can head straight for the paint. You need to fill holes, spackle and sand*, maybe even cut a new piece of drywall in to the existing wall.
Many professional painters use a tinted primer before painting. This is an inexpensive way to bring your walls close to their final intended color before adding the more pricey topcoat.
This is essentially a chalk paint product with primer and top coat built in. This paint is good for indoor and even outdoor projects too. The built-in primer and top coat make painting almost any surface a breeze, with little to no prep work required.
If you are interested in experimenting with a no-makeup look, then using a primer alone is a great option. You can still experience the soothing benefits of the product that work to reduce redness and irritation. Using primer without makeup can also let you enjoy the subtle glow it brings to your complexion.
So if your room needs 2 coats, plan on getting around 200 square feet out of a gallon. Two gallons would allow for two coats of coverage over roughly 800 square feet. Most people will commonly buy this amount as it covers common-sized spaces like a living room or larger bedroom.
Patchiness usually happens if you don't use enough paint, or apply it unevenly. Using a touch more paint, and painting in small sections one at a time, usually does the trick. Also, rolling in a grid fashion will get you an even finish too. But, sometimes, changes in the gloss level leave things patchy.
Using too much primer may make your skin slippery and oily, especially if you're using a product containing silicones or hydrating ingredients. Be careful with colour-correcting primers, focusing on areas of discolouration. If you use too much of a green primer, you may look sickly.
The primer coat doesn't have to be perfect, but it should cover the surface (no bare spots) and it shouldn't be so blotchy that you get drips or visible unevenness.
Over-thinning your paint or applying it too thinly can also cause it to split. Conversely, a heavy hand while painting can lead to what's called mud cracks, where too-thick paint dries with a clumpy, swollen look. Not allowing adequate dry time between coats can also lead to these problems.
You will want to use 2-3 coats of primer to ensure there is a good bond between the new paint and the wall, and also to cover up any previous colors, especially if they are red, orange, or a strange outdated color. In short, you will typically need 2 coats of primer for most painting projects.
Summary. For your finish to be vibrant and not dull sanding after primer will ensure that the finish is not excessively dulled when you apply your paint top coat. You will typically use finer grit sandpaper and aim to achieve a smooth wood finish so that you get a fine appearing wood finish when you apply your topcoat.
Too much primer causes a different set of problems. Too many layers or an excessively thick layer increases the risk of the primer cracking, crazing, or chipping. It also takes longer to dry, slowing down your redecorating work. In the worst case scenario, it can damage drywall by causing it to bubble and peel.