Epoxy
12-15-2008, 03:12 AM
#26
Senior Member
My Feedback: (14)
RE: Epoxy
ORIGINAL: DavidAgar
I prefer the Bob Smith brand. I have never had a failure, however you do need to make sure that it is mixed 50/50 or it will fail. I have used some brands over the years that were not as user friendly and would not set up no matter how close you were on the mixing. I have also used Pacer which is just as good as Bob Smith, however you still need to watch your mixing ammounts. Good Luck, Dave
I prefer the Bob Smith brand. I have never had a failure, however you do need to make sure that it is mixed 50/50 or it will fail. I have used some brands over the years that were not as user friendly and would not set up no matter how close you were on the mixing. I have also used Pacer which is just as good as Bob Smith, however you still need to watch your mixing ammounts. Good Luck, Dave
Most epoxy glues have a useful shelf life of only 18 months. Using it after that much time has passed is chancy and not recommended by many manufacturers.
As others have mentioned, proper proportions and thorough mixing is absolutely necessary. Keeping epoxy out of the sunlight is also mandatory. Most epoxy have a weakness when it comes to UV exposure. Some manufacturers even offer a UV proofing additive for their epoxy glues when the glues are expected to hold up to constant UV epoxure (West Systems).
Now, how long has that epoxy set been sitting in your local hobbyshop or hardware store? Are you sure? That's why I buy my epoxy from stores that I know move a lot of said product. Wal-Marts, Ace, Home Depot, Lowes and other stores typically have a high turn over rate in most products.
My favorite epoxy is Devcon for 5-minute stuff. I was a real Hobby-Poxy fan when I could find it. Is it still available today? Their 45 minute epoxy was really good stuff.
Ed Cregger
12-15-2008, 06:01 PM
#27
RE: Epoxy
The most common reason for poor cure results from epoxy is low temperature, which should be above 70 degrees F during the entire cure time. This does not apply to the 5 minute epoxies since the curing process produces enough heat for a full cure to occur even at 50 degrees or below. I have found temperatures around 80 degrees result in the slower drying epoxies curing to their maximum potential strength. Epoxies with around a two hour working time will take about 24 hours to fully cure and keeping the surrounding tempertures high enough for that period of time can be a problem, especially in a garage during winter time. An option is to cover the parts during the curing time with a large cardboard box and put a lamp in it (a cheap curing oven).
I have found the best mixing surface to be the flexible plastic tops that are used on coffee cans and other products. The lip around the top restrains larger epoxy mixes and the cured left over epoxy just pops off then you flex the top so that the same top can be reused for years. If you don't have a scale, the best way to get equal amounts of each component is to run equal length beads parallel to one another, then thoroughly mix them together for at least 30 seconds. I disassemble clothspins to produce two excellent mixing sticks that are much more rigid than popsicle sticks. I cut the end off of one to form square edges at the end for use when mixing finishing epoxy in a cup so that it will reach the epoxy in the corners at the bottom of the cup.
Heating the epoxy is the best way to make it thin, but it will also shorten the working time. 92-99% isopropyl alcohol is what works best if you do thin it. Do not use rubbing alcohol since it contains 30% water. Denatured alcohol has ingredients in it to make it undrinkable, but who knows what those ingredients are? I have found that acetone works best for cleaning up epxoy, but it always seems to change the curing characterists when used for thinning. The use of finishing epoxies are your best choice when you need a thin epoxy for laminating or sheeting foam wings.
Some epoxies you can buy will crystalize in the bottle, sometimes in less than two years. But there are epoxies in your LHS that don't have this problem. Over time, epoxies can absorb moisture. When this happens, you can take the tops off the bottles and put the resin component in a microwave overn for 15 second, the hardener for 20 seconds. This will "freshen" the epoxy to as good as new. I like to do this in the winter time before mixing the component when the bottles feel cold, but I put them in for only 10 and 15 seconds.
LHS epoxies have some margin for error for mixing ratio. An equal volume of part A & B is best, but if you weigh those volumes you will find that the resin is 10% heavier than the hardener. Mixing by weight, therefore, mean you are using a larger volume of hardener. I have not seen any change in characterists in the cured epoxies whether they are mixed by volume or weight, so there appears to be at least a 10% leeway when mixing at a 50-50 ratio.
I have found the best mixing surface to be the flexible plastic tops that are used on coffee cans and other products. The lip around the top restrains larger epoxy mixes and the cured left over epoxy just pops off then you flex the top so that the same top can be reused for years. If you don't have a scale, the best way to get equal amounts of each component is to run equal length beads parallel to one another, then thoroughly mix them together for at least 30 seconds. I disassemble clothspins to produce two excellent mixing sticks that are much more rigid than popsicle sticks. I cut the end off of one to form square edges at the end for use when mixing finishing epoxy in a cup so that it will reach the epoxy in the corners at the bottom of the cup.
Heating the epoxy is the best way to make it thin, but it will also shorten the working time. 92-99% isopropyl alcohol is what works best if you do thin it. Do not use rubbing alcohol since it contains 30% water. Denatured alcohol has ingredients in it to make it undrinkable, but who knows what those ingredients are? I have found that acetone works best for cleaning up epxoy, but it always seems to change the curing characterists when used for thinning. The use of finishing epoxies are your best choice when you need a thin epoxy for laminating or sheeting foam wings.
Some epoxies you can buy will crystalize in the bottle, sometimes in less than two years. But there are epoxies in your LHS that don't have this problem. Over time, epoxies can absorb moisture. When this happens, you can take the tops off the bottles and put the resin component in a microwave overn for 15 second, the hardener for 20 seconds. This will "freshen" the epoxy to as good as new. I like to do this in the winter time before mixing the component when the bottles feel cold, but I put them in for only 10 and 15 seconds.
LHS epoxies have some margin for error for mixing ratio. An equal volume of part A & B is best, but if you weigh those volumes you will find that the resin is 10% heavier than the hardener. Mixing by weight, therefore, mean you are using a larger volume of hardener. I have not seen any change in characterists in the cured epoxies whether they are mixed by volume or weight, so there appears to be at least a 10% leeway when mixing at a 50-50 ratio.
