To extend the shelf life of house paint, first keep out the air
By Gene Gary
Copley News Service
Q: I am semiretired and I refurbish homes, so I do a lot of painting. There's always extra paint left over which can come in very handy for touch-up jobs later. Yet I find that most of the paint I store in original cans is almost unusable after any length of time. Water-based paints do not keep well in cans, which tend to rust. And I find paints often separate and become unusable. I've even had a can or two grow glorious mildew colonies. Is it just that water-based paints are so inferior to oil-based paints that they don't store well?
I would be interested in what paint manufacturers have to say about how long these remnants can be kept, and what containers or storage methods they recommend.
A: The key to long-term storage of paints is an airtight environment. Water-based paints contain ammonia. It is the ammonia vapor that attacks protective linings of paint cans. This leads to surface rust and damaged paint. If you transfer leftover paint to airtight plastic containers, the threat of rust is eliminated. Furthermore, you should place these containers upside down on storage shelves. This way the airtight seal is further assured because now the air pocket in the container is fully insulated and not subject to failure of the lid seal. This will also minimize the thick, scumlike surface that forms over once-opened paint.
If you are only storing paint for a short time and wish to keep it in its original container, there are other methods of ensuring a tight seal.
Once a container has been opened, paint tends to accumulate in the lid groove, and leaving paint there impairs a good seal. To prevent this buildup, use a nail to punch several holes in this groove before you paint. When you reseal the can, the lid will cover the holes and form a tight seal (be sure and wipe as much excess paint from the rim as possible prior to closing). A piece of plastic wrap stretched over the rim prior to placement of the lid will also improve the seal. Set the lid into place over the plastic and secure it with a light hammer, tapping on alternate sides of the lid.
Another method of keeping leftover paint fresh is to transfer it into a resealable plastic bag. Squeeze the air out before you seal the bag; then put the bag into the original paint can and tap the lid closed. It's wise to transfer leftover paint into smaller containers if the original can is only half full. You are then dealing with a smaller amount of airspace that tends to dry up paint.
Another preventive measure is to cut a circle of heavy wax paper that is the same diameter as the interior of the can and float it on the paint surface. The wax paper acts as a barrier, reducing the interaction of the oxygen and paint.
If you are dealing with oil-based paint, spray a thin film of mineral spirits over the surface of the paint prior to resealing the can. Use only one teaspoon to a half-empty gallon of paint. This will provide the same type of barrier as the wax paper on latex paints. Keep the film intact as you seal and store the can. Take care not to shake or agitate it.
When you go to use stored paint, strain lumps in it by pouring it into an empty can covered with cheesecloth. Hold the cheesecloth in place with a sturdy rubber band, tape or string.
Even if paints are correctly stored, paint separation can still occur, regardless of its quality. Color enhancers separate from the paint base, which can be corrected by simply stirring the paint. The ingredients easily combine.
Biocides mixed into today's paint by the manufacturer will stop bacterial growth. This, combined with an airtight environment, should prevent mildew problems. Paints can be stored in any standard well-ventilated room. They should never be used or stored around an open flame, such as a gas water heater.
If you live in a colder climate, be sure your water-based paints are stored away from freezing temperatures.
As far as quality of the newer water-based paints, manufacturers say that today's technology has advanced acrylic latex paints to the point that their durability and application parallels or even exceeds oil-based products.
Q: I just purchased a light fixture that requires four individual bulbs. A sticker on the fixture advises that the wattage on each bulb should not exceed 60 watts. Most of my light bulbs are 100-watt and seem to be fine for most fixtures. Why would this fixture call for lower-wattage light bulbs?
A: The bulb-wattage warning is there to protect you from fire hazard. The higher the wattage of a light bulb, the more chance there is for heat buildup. This is true of incandescent lights only because fluorescent tubes do not produce excessive heat. Multiple lamps within a fixture are often limited in wattage to curtail overall heat buildup in that particular fixture. This is particularly important in recessed and flush-mounted ceiling light fixtures where there is no air circulation around the fixture to cool bulbs. Be sure and follow the manufacturer's directions on wattage limitations to ensure that heat buildup stays in a safe range and there is no risk of fire.
Send e-mail to copleysd@copleynews.com or write to Here's How, Copley News Service, P.O. Box 120190, San Diego, CA 92112-0190. Only questions of general interest can be answered in the column.