Drywall Primers vs. Drywall Sealers
Imperfections in drywall are very common. These imperfections, however, can be traced to a wide variety of causes. Frequently, the cause may be poor or unskilled workmanship. Often the imperfections can be traced to lumber shrinkage. High humidity and large temperature swings during installation and finishing can cause problems. Poor carpentry techniques also can be to blame. However, did you ever think that a problem could arise in the paint that you use?
Resins and Fillers
Paints are a combination of ingredients. No two paints are exactly alike. Chemically speaking, paints are almost identical to adhesives. Paints primarily have three ingredients: Resin, vehicle and pigment.
The resin in a paint is the glue that allows it to stick to a surface. The resins are usually clear and almost always encapsulate or surround each pigment particle.
The vehicle is the ingredient which allows paint to be a liquid in the can. I often refer to it as a temporary ingredient, for once you apply the paint to a surface, the vehicle evaporates into the air. That is why you must ventilate a room when using a paint that contains hydrocarbons or flammable solvents. These liquids turn into a vapor and can either make you sick or, if ignited, explode.
Pigments are the ingredients which impart color. They are solid particles comprised of many ingredients. Without resins, the pigments would not stick to the surface you paint. They would simply wash off. In fact, that is exactly what happens with exterior paints that chalk. The resin which is exposed to the weather breaks down and releases the pigment particles. The pigment then washes down onto your brick, foundation or driveway.
Primers vs. Sealers
Just about everyone who has painted something has heard of primers. Some of us have also heard of sealers. Did you know that there is a big difference? These two foundation paints have entirely different qualities.
Primers are specially formulated paints that are used to smooth out the surface you are painting. They have great filling capabilities. Because they have a high solid (pigment) content, these solids can fill in any microscopic valleys, depressions, etc. Primers are usually low in resin, so that when they dry, the surface of the primer film is coarse . This allows the finish paint an excellent surface to grab onto.
Sealers, on the other hand, are exactly opposite of primers. They have a high resin content and a low solid (pigment) content. Sealers are formulated to regulate the rate of absorption of the finish paint. This quality is achieved by the high resin content. The resin, when dry, creates a barrier. Finish paints cannot easily soak through sealers.
Different materials absorb liquids at different rates. Materials such as these are said to have different porosities. Finish paint which is applied to a surface that has several different porosities will not dry at equal rates. Those areas of the surface which absorb the paint quickly will pull the paint (and paint particles) deeper into the surface. The sheen of the paint will appear uneven, even though the surface which was painted is smooth!