There is that particular frustration when you break open the lid of a not-quite-full gallon of paint and discover a large rubbery skin sitting on top. After spending all that time hunting down the elusive “eggshell” or “misty morning,” the expensive liquid has become a useless lump that cannot be practically returned to its former state. Most people simply slam the tin lid back on, but the fact is that common paint cans have a bad habit of allowing small amounts of air through.In order to prevent your leftover paint from being wasted, all you need is something that lies right in your kitchen drawer, along with the aluminium foil. All you need to do is use a thin layer of plastic wrap on top of the paint before you seal the lid. This way, your paint will get an extra gasket and will not dry easily.The chemistry of the “skin” formationTo understand why your paint becomes useless, you should see it as a process that takes place chemically rather than simply drying out. Paints are not meant to just dry off by coming in contact with oxygen, like other liquids such as water would. In reality, paints are made through a process of bonding the molecules together.According to research conducted by Construction and Building Materials, the key causes of material breakdown include loss of moisture and exposure to air. In case a container is not tightly sealed, the liquid in it evaporates due to which oxygen acts on it, causing it to harden. Putting plastic wrap on top stops this from happening.
This prevents air exposure, stopping the formation of a rubbery skin. This simple technique preserves the paint’s moisture and mechanical integrity for future use.
As one would imagine, even the smallest flow of air is enough to affect the mechanical characteristics of the paint. The soft, malleable seal – picture wrapping your sandwich in plastic foil – closes up these microns between the metal lid edge and the body of the paint can, locking up the paint in a vacuum of sorts that keeps all moisture and air locked out.Keeping your paint in its prime mechanical conditionThe point here is not just the retention of moisture in the paint, but its mechanical integrity. Should the paint begin to dry off even slightly in the can, it will no longer be able to form proper bonds when applied to your walls.According to a study regarding the Shrinkage and mechanical properties of drying oil paints, the drying process involves significant physical stresses. As the liquid components evaporate, the remaining paint begins to shrink and pull inward. This is what causes that tough “skin” to form on the surface. If you stir that skin back in, you are essentially adding tiny bits of solid plastic into your liquid paint, which will ruin the smooth texture of your next coat.One thing is certain, according to the study: maintain the moisture content of the paint, and its strength will remain unaffected. By using the plastic wrap technique, we end up with a micro-environment with a cushion. The headspace that forms will remain moist; thus, a film will never develop.Tips for sealingTo make this technique work, here are a few things you should do. First, clean the rim of the can using a wet cloth before sealing. If the paint is dry on the rim, there is no way that the lid can be completely sealed, regardless of your efforts to use plastic wrap. Once you have cleaned the rim, cut a piece of plastic large enough to cover the rim by about two inches.Press the wrap down so it is in contact with the surface of the paint, if possible, or stretch it tightly over the top. Then, place the lid on and tap it down firmly with a rubber mallet. For an extra layer of protection, some DIY enthusiasts store their cans upside down after wrapping them. This allows the paint itself to act as an additional liquid seal against the lid, though you should only do this if you are confident in your plastic wrap gasket.With this simple, kitchen-based practice, you protect your valuable investment and ensure that each home improvement looks perfect. It is an environmentally friendly method that will allow you to use your favourite colours whenever you feel inspired to do so.
