Charlee
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- Dec 29, 2010
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The magazine Model Aviation asked BSI what are the most frequently asked questions that we receive. This is what we sent them:
I have had great success with 30 minute epoxy, but on my last batch the epoxy never fully hardened and still feels tacky. What could I have done wrong?
Improper mixing or ratios of the two parts could be the problem, but over 90% of the time the situation is caused by the epoxy curing in an environment below 70°F. It must be above this temperature for the entire 8 hour full cure time of the epoxy to have maximum strength. 5 minute epoxy is less sensitive to temperature since it creates a significant amount of its own heat when curing.
What is the best way to store CA glue? Should I keep open bottles in my freezer?
Exposure to heat and moisture are the two main factors in decreasing the shelf life of cyanoacrylates (CA). If kept at normal room temperature (74°F) and low humidity levels, good CAs will have a shelf life of over two years. Unopened bottles can be stored in a freezer, but this offers little or no advantage over storage in a refrigerator. CA bottles can be refrigerated in a sealed container with a packet of desiccant (silica gel) inside to extend their shelf life. Opened bottles that are frequently used should not be put into the fridge since condensation can occur inside the bottle.
I mixed half of the contents of each bottle of 30 minute epoxy in a small dish and after less than ten minutes it became very hot and solidified. Why did this happen?
When the two components of epoxy are mixed together, they create an exothermic reaction. If the resulting heat is not allowed to dissipate it can cause the cure time of the epoxy to accelerate drastically. This will happen when larger quantities (more than an ounce) are mixed in a cup. The container traps the heat, which speeds the cure, which creates more heat, etc, etc. If the mixture is stirred every minute, it will allow some of this heat to be released. Pouring the epoxy onto or mixing it on a flat surface will allow the heat to disperse and is the best way to get the full working time of the epoxy.
What do you recommend mixing into epoxy to make it thinner? Also, can I add a color to it?
Heating epoxy will make it thinner, but this also lowers your working time. 91%-99% isopropyl and denatured alcohols are the best solvents to add to epoxy for thinning, with 10%-20% being enough to sufficiently lower the viscosity of the epoxy. Do not use rubbing alcohol. While it can be used for the cleanup of uncured epoxy, it contains 30% water and has an adverse effect on the curing process. Acetone can be used but is more likely to change the cured properties of the epoxy. Acrylic or latex paint can be used to color epoxy, but concentrated tints in paste form (like Tints-All) work best.
Regular CA fumes really irritate my eyes and nose. Can I use foam-safe odorless CAs for balsa construction?
The best foam-safe CAs are also odorless and are the best alternative for modelers who have developed a sensitivity to the fumes that are an irritant emitted by regular CAs (these fumes do not contain anything related to cyanide like some have claimed). Modelers do not have to sacrifice any significant performance characteristics when they use good foam-safe CAs on other materials like wood and plastic. The gap filling odorless CAs can also be used on clear plastics, like canopies, without producing the fogging that occurs when regular CA fumes settle on a surface. The only disadvantages are their prices and slightly lower shelf life.
Should I be mixing epoxies by equal volume or weight? Also, can I add more hardener to speed the cure?
The resins of most epoxies are heavier than the hardeners by a 1.1 to 1 ratio. As long as the epoxies are mixed in equal amounts within a 10% margin of error, there will be no distinguishable difference in the cured characteristics if done at the proper temperature. This margin allows the epoxies to be mixed with equal volume or equal weight with the same results. Additional hardener should never be intentionally added to “improve” the curing of epoxy. As a general rule, each molecule of resin needs to have a matching molecule of hardener for optimum results. If all the resin molecules already are attached their “partner,” any excess hardener molecules will be left floating in the mix, which will degrade the cured properties of the epoxy
How can I slow the curing of CA?
The bonding time of CA increases significantly in temperatures below 45°F. Using a bottle of CA immediately after it has been stored in a refrigerator or freezer will give modelers the extra time they may need.
I have had older epoxy became considerably thickener or cloudy in the bottles. Can it still be used?
Even the best epoxies can absorb moisture over time and become as described. After taking their nozzle tops off, the bottles can be put into a microwave oven for about 15-18 seconds (three seconds less for the black-capped resin since it heats faster). This eliminates the moisture and rejuvenates the components to near new condition.
Why would I ever need to use CA accelerator? CAs bond so quickly I don't think I would need them to be any faster.
Whenever you are bonding material with the thicker CAs, some of the CA will usually ooze out of the joint. Even though the parts may be firmly bonded within 5-10 seconds, the excess CA can remain liquid for several minutes. Spraying the joint with the Insta-Set will harden this CA in less than ten seconds so you can handle the parts without fear of bonding your fingers to them. For stronger construction, fillets can be formed with thicker CA in the corners of 90° joints and then sprayed with accelerator. Materials with high acid content, very dry wood, low surface energy plastics and foam do not have the correct chemistry to initiate the polymerization of CA. This is when it's necessary to use accelerator to get any kind of instant bonding.
I have a bottle of older CA that has gotten thicker. Can I add acetone to the CA to bring it back to its original thickness?
The only fluid that you can add to CA is other CA. Anything else will cause the CA to harden in the bottle within days. Thin CA can be added to the thicker CAs to create any consistency you want. No additive will bring thickened thin CA back to its original water thin consistency.
I have had great success with 30 minute epoxy, but on my last batch the epoxy never fully hardened and still feels tacky. What could I have done wrong?
Improper mixing or ratios of the two parts could be the problem, but over 90% of the time the situation is caused by the epoxy curing in an environment below 70°F. It must be above this temperature for the entire 8 hour full cure time of the epoxy to have maximum strength. 5 minute epoxy is less sensitive to temperature since it creates a significant amount of its own heat when curing.
What is the best way to store CA glue? Should I keep open bottles in my freezer?
Exposure to heat and moisture are the two main factors in decreasing the shelf life of cyanoacrylates (CA). If kept at normal room temperature (74°F) and low humidity levels, good CAs will have a shelf life of over two years. Unopened bottles can be stored in a freezer, but this offers little or no advantage over storage in a refrigerator. CA bottles can be refrigerated in a sealed container with a packet of desiccant (silica gel) inside to extend their shelf life. Opened bottles that are frequently used should not be put into the fridge since condensation can occur inside the bottle.
I mixed half of the contents of each bottle of 30 minute epoxy in a small dish and after less than ten minutes it became very hot and solidified. Why did this happen?
When the two components of epoxy are mixed together, they create an exothermic reaction. If the resulting heat is not allowed to dissipate it can cause the cure time of the epoxy to accelerate drastically. This will happen when larger quantities (more than an ounce) are mixed in a cup. The container traps the heat, which speeds the cure, which creates more heat, etc, etc. If the mixture is stirred every minute, it will allow some of this heat to be released. Pouring the epoxy onto or mixing it on a flat surface will allow the heat to disperse and is the best way to get the full working time of the epoxy.
What do you recommend mixing into epoxy to make it thinner? Also, can I add a color to it?
Heating epoxy will make it thinner, but this also lowers your working time. 91%-99% isopropyl and denatured alcohols are the best solvents to add to epoxy for thinning, with 10%-20% being enough to sufficiently lower the viscosity of the epoxy. Do not use rubbing alcohol. While it can be used for the cleanup of uncured epoxy, it contains 30% water and has an adverse effect on the curing process. Acetone can be used but is more likely to change the cured properties of the epoxy. Acrylic or latex paint can be used to color epoxy, but concentrated tints in paste form (like Tints-All) work best.
Regular CA fumes really irritate my eyes and nose. Can I use foam-safe odorless CAs for balsa construction?
The best foam-safe CAs are also odorless and are the best alternative for modelers who have developed a sensitivity to the fumes that are an irritant emitted by regular CAs (these fumes do not contain anything related to cyanide like some have claimed). Modelers do not have to sacrifice any significant performance characteristics when they use good foam-safe CAs on other materials like wood and plastic. The gap filling odorless CAs can also be used on clear plastics, like canopies, without producing the fogging that occurs when regular CA fumes settle on a surface. The only disadvantages are their prices and slightly lower shelf life.
Should I be mixing epoxies by equal volume or weight? Also, can I add more hardener to speed the cure?
The resins of most epoxies are heavier than the hardeners by a 1.1 to 1 ratio. As long as the epoxies are mixed in equal amounts within a 10% margin of error, there will be no distinguishable difference in the cured characteristics if done at the proper temperature. This margin allows the epoxies to be mixed with equal volume or equal weight with the same results. Additional hardener should never be intentionally added to “improve” the curing of epoxy. As a general rule, each molecule of resin needs to have a matching molecule of hardener for optimum results. If all the resin molecules already are attached their “partner,” any excess hardener molecules will be left floating in the mix, which will degrade the cured properties of the epoxy
How can I slow the curing of CA?
The bonding time of CA increases significantly in temperatures below 45°F. Using a bottle of CA immediately after it has been stored in a refrigerator or freezer will give modelers the extra time they may need.
I have had older epoxy became considerably thickener or cloudy in the bottles. Can it still be used?
Even the best epoxies can absorb moisture over time and become as described. After taking their nozzle tops off, the bottles can be put into a microwave oven for about 15-18 seconds (three seconds less for the black-capped resin since it heats faster). This eliminates the moisture and rejuvenates the components to near new condition.
Why would I ever need to use CA accelerator? CAs bond so quickly I don't think I would need them to be any faster.
Whenever you are bonding material with the thicker CAs, some of the CA will usually ooze out of the joint. Even though the parts may be firmly bonded within 5-10 seconds, the excess CA can remain liquid for several minutes. Spraying the joint with the Insta-Set will harden this CA in less than ten seconds so you can handle the parts without fear of bonding your fingers to them. For stronger construction, fillets can be formed with thicker CA in the corners of 90° joints and then sprayed with accelerator. Materials with high acid content, very dry wood, low surface energy plastics and foam do not have the correct chemistry to initiate the polymerization of CA. This is when it's necessary to use accelerator to get any kind of instant bonding.
I have a bottle of older CA that has gotten thicker. Can I add acetone to the CA to bring it back to its original thickness?
The only fluid that you can add to CA is other CA. Anything else will cause the CA to harden in the bottle within days. Thin CA can be added to the thicker CAs to create any consistency you want. No additive will bring thickened thin CA back to its original water thin consistency.
