Some of you probably know this already but thought I would pass it on for those who may not. I called Aircraft Spruce and asked them what the shelf life on clear Nitrate and Butyrate dope was. They did not know so they gave me the number of Certified products and I called them. Here is what they told me. Clear Nitrate has a shorter shelf life than Butyrate but essentially they are about the same...2 years. Something happens to the PH of the product and that is why it turns amber color in the can after about 2 years. He suggested that I should not use it as the adherence of the product to material is diminished.
Mike
Hi Mike,
Just saw this thread so I went back a few days & copied a posting I wrote that included my experience with shelf life of nitrate & butyrate dope:
"John, buying butyrate dope in small quantities such as pints is the most expensive way to buy it. For instance, Sig lists butyrate Lite-Coat at $15.99 per pint, and they list it for $26.29 per quart. That is a little over 50% greater price for twice as much product. If you buy dope a pint at a time, which is not enough for even one project (at least for me), then it will be very expensive. For my models I buy butyrate dope a gallon at a time which is much less expensive per unit volume;
the dope will keep for a long time if you store it properly. Always put the lid back on tightly right after you pour some out for use, don't store it where the temperature gets over 100 degrees F, and don't open the can when the humidity gets much over 75% as that will allow moisture to get into the can. In my full-scale airplane restoration business I have gallon & five gallon containers of butyrate dope that are 15 years old and still work just fine. The main way that dope deteriorates is to become acidic due to absorbing moisture and/or being stored in the wrong kind of metal container. You can tell if it has become acidic: the color will become noticeably amber & will have a different smell than when fresh.The other thing that I do to minimize the cost of dope for my models is to use Randolph butyrate dope for all of the buildup & colors (Randolph offers a huge selection of colors & Aircraft Spruce will send to you a color chart for free), and Sig Lite-Coat for the top coat clear. Randolph is a very high quality product, however I have found Sig to be more fuel-resistant than any other brand of dope. For instance, the Aircraft Spruce price for a quart of Randolph A-1690 butyrate dope, non-tautening clear is $14.50. Randolph 9703 butyrate thinner (which works just fine in Sig or any other butyrate dope) is $8.45 per quart and $25.40 per gallon."
The guys at Consolidated Aircraft Coatings who own Poly-Fiber process, Ceconite process, and Randolph line of paints & dopes as well as other dope products manufacturers will always be conservative when asked about the shelf life of their products. They are very knowledgeable and honest, but they are giving you the worst case situation. If some of the dope is, in fact, poured into another container for use, then the original container left to sit with the lid off for a period of time it will lose solvents through evaporation and absorb moisture in a humid atmosphere. Storing the dope in high temperatures (say, above 100 degrees F), particularly if used under the conditions stated above will lead to deterioration of the dope.
Another thing that I forgot to mention above is don't use a metal stirring stick; I have several aluminum stirring paddles provided by Sikkens marked with graduations for various ratios for mixing catalyst & reducer that I use with Sikkens polyurethane, but I don't use them with nitrate or butyrate dope. The metal stick will scratch the coating inside the metal container the dope comes in & lead to the PH change and the dope becoming acidic. Use a wood stirring stick.
Topic: Shelf Life on Clear Nitrate and Butyrate Dope (Read 10187 times)