When you go into a supermarket, you can look at the food containers and find a sell-by date. But when finishers shop for finishing materials, we can only find the date the materials were manufactured, and we never see a shelf life or an expiration date marked on the labels.
You can find the package life for most finishing products on Product Data Sheets. These information sheets are free and available from manufacturers and their suppliers, and they are yours for the asking.
There are several reasons why shelf lives are not listed on the labels. Let’s begin with the dyes and dry pigmented powders that are used for coloring. These dry powdered materials do not go bad and can last indefinitely, as long as they are kept dry and out of direct sunlight.
The pigmented paste colorants — like the Universals, Oil and Japan colors — can cause problems because of the different solvents and additives that are used in the milling and mixing process to get uniform color and paste consistency. These additives oxidize because of the opening and closing of the cans, causing the paste colorant to harden and then “skin over.” These products must be mixed well and kept sealed when not in use.
We find these same conditions in most stains and colored glazes that contain certain synthetic alkyd binders, including any of the drying oils like tung or boiled linseed oil.
It is very important that you tighten the caps and lids on all of your containers as soon as possible, which will reduce contamination from oxygen and moisture. Keeping your materials in closed cabinets will help. It’s also important to mark all of your containers with the date on which you first acquire them. You want to be sure to use the oldest materials first, so you have the newest materials in your cabinets.
They can’t stand the heat
The temperature in your shop also will play a very important part in the shelf life of your materials, as some finishes such as pre-catalyzed lacquers already contain the needed catalyst that was added to the coating when it was produced. This can begin to harden prematurely in the high temperatures of summer.
Colder temperatures also will affect some of the water-based products, including glues, which tend to separate in this kind of weather.
Certain emulsions that are in suspension, like water and oil types of polishes, waxes, and polishing compounds, are affected by erratic temperature changes, which will take the components out of suspension and make these products useless. Products that contain water can become discolored over time because the insides of the cans will begin to rust.
We all know that the soft and hard wax sticks used for filling in defects will melt in the high summer heat, and harden and crack in the colder temperatures. These conditions will also affect the harder burn-in sticks and other kinds of fillers.
It’s very important to get to know your products, because some don’t go bad if stored properly, while others deteriorate if the air or the high moisture content in the shop gets into the products. Keeping them mixed and tightly covered will help some. Adding some marbles, pebbles, or gravel into the containers, filling the space of the used-up product, will retard the drying of alkyd oil finishes. Bloxygen, which is a mix of nitrogen, carbon dioxide and argon gases, is also used to fill the container and prevent the oxygen from drying out the oils.
When in doubt …
To be honest, no one can predict the shelf life of most of the finishing materials, even when the manufacturers list one. There are too many variables that can’t be controlled. Manufacturers can test these products under these conditions, but there are no guarantees all the products will always pass the test. Then again, there are many products that will go way beyond the shelf life and are still usable.
Using outdated products, in many cases, will provide poor adhesion and elasticity. They will not be able to expand and contract, and will crack or check in a short time. If you can’t spend the time to sample outdated materials, it may be better to discard them and use “fresh” cans.
Many finishers still use the expression “when you are in doubt, throw it out.” It’s just not worth taking a chance on using them for your fine finishing.
Mac Simmons is a freelance writer and 50-year veteran of the furniture finishing, refinishing and restoration trades.
This article originally appeared in the October 2008 issue.