Glues

under construction

 

Part 1: cyanoacrylates

Thin CA (cyanoacrylate adhesive and sold under the names of: Hot Stuff, Zap CA, Jet and Alteco) has a consistency resembling that of water and is used mainly for bonding parts which fit very well. Because it is water thin, maximum contact at the joint is necessary. Good examples of maximum contact joints would be: two pieces of smooth flat wood, plastic, rubber, leather, glass or any number of other materials, in any combination, which have smooth tight-fitting contact areas. Thin CA, because of its water-thin consistency, has the ability to penetrate the tightest crack in any object or the tightest joint between two objects. The degree of penetration depends on the porosity of the material. As an example, penetration would be maximum between two pieces of glass and minimum between two pieces of cork simply because the cork itself would tend to soak-up the thin CA as it was applied. Thin CA cures very fast (usually 3-5 seconds). If too much is used for a given bond, curing will take longer.

Thick CA (cyanoacrylate adhesive and sold under the names of: Super T, Zap-a-gap, Super Jet and Alteco) has a consistency similar to that of syrup and has the ability to fill small gaps between parts which don't fit perfectly. In other words, where the best fit that can be hoped for is minimum contact. Good examples of minimum contact would be repairing a break in a piece of wood, or bonding one piece of wood, plastic, rubber, ceramic, etc. into a slot which is slightly oversize. Thick CA cures at a slower rate than thin CA (usually 1O-25 seconds depending on the material). If too much is used for a given bond, curing will take longer.

Very thick CA (cyanoacrylate adhesive and sold under the names of: Special T and Slow Jet) has a consistency resembling mixed epoxy at room temperature. Very thick CA has a greater gap-filling ability than thick CA and is much more positionable after contact of parts. The rate of cure is slow enough, (usually 3O-5O seconds depending on the material), to allow precise alignment of parts after assembly. If too much is used for a given bond, curing will take longer.

Accelerators (Hot Shot, Zip Kicker) are used with all types of CA glues and with it you can do almost magical things. Why an accelerator when super glues are so fast anyway? They work in four ways to make CA glues easier, faster, stronger and able to bond some of the most unusual materials you can think of. Easier - because you can decide how fast the cure should be even on pitchy woods that often take longer to bond. Faster - because accelerators contain special ingredients which clean the bonding surface and act as a catalyst to start the thermal reaction resulting in curing even at low temperatures. Stronger - because the cleaner the surface is from the oils that can be found in almost anything, due to handling or oils which are deposited naturally from the air, the better the bond.

Getting Started. Hold the bottle upright and flick the spout lightly with your finger. This draws the glue from the upper spout back into the bottle before opening. Cut 1/16" off the end of the spout for the smallest opening. To increase the glue flow, cut the spout tip off an additional 1/16" or until desired flow is obtained. Note: Once opened, it is best not to plug the hole with pins etc. when storing. This only increases the likelihood of future clogging because moisture is one of the catalysts for CA glue. Anything put into the spout has trace moisture on it. The spout should be sealed with the overcap attached to the bottle. It is best to wipe off the spout before sealing with the overcap. Store the opened bottle upright and at room temperature.

Using Thin CA (Hot Stuff) Keep in mind two important characteristics of Hot Stuff

  1. a water-thin consistency
  2. fast curing (3-5 seconds).
Assemble the parts first. All alignment will be done before Hot Stuff is applied. With the parts held firmly together, apply a SMALL amount of Hot Stuff to the joint or crack. You will notice how it disappears into the crack. What actually happens is that Hot Stuff follows the joint or crack as if it were a maze except all paths are followed at the same time. As long as it keeps disappearing, its penetrating farther into the crack. The size of the part and it's porosity play an important role in knowing how much to apply. Some examples: bonding two squares of plastic 1" by 1" would require only a drop or two applied to only one side because plastic is relatively nonporous. Two pieces of balsa wood, the same size would require more however, because the Hot Stuff tends to soak into the pores of the wood at the same time its following the crack or joint. This, of course, reduces the amount of joint penetration making it necessary to apply one drop on each of the four sides. As mentioned before, too much Hot Stuff slows the rate of cure. It's also helpful to remember that once the crack has been penetrated there is no place for the glue to go except outside the parts.

Using Thick CA (Super T). Use Super T just like you would use a pre-mixed epoxy or white glue, an alaphatic resin or any number of other old fashioned glues. The difference becomes apparent once the parts are assembled. Super T is thicker than Hot Stuff, is gap filling and has a slower rate of cure making it possible to bond parts which fit poorly (limited contact area). Because it's cure rate is slower (1O-25 seconds), a few seconds of alignment time is possible after joining parts. Apply Super T in a spiral pattern to one part, assemble and align parts, then hold firmly for 1O to 25 seconds.

Using Very Thick CA (Special T). Special T is used just like you would use a pre-mixed epoxy, or white glue, an alaphatic resin or any number of old fashioned glues. Again, the difference becomes apparent once the parts are assembled. Special T is very thick, has greater gap-filling capabilities and has a slower rate of cure than Super T making it possible to bond parts which fit very poorly (limited contact area). Because it's rate of cure is so slow (3O to 5O seconds), many seconds of alignment time is possible after joining the parts. The amount of time varies, of course, with the material being bonded. Apply Special T in a spiral pattern to one part, assemble and align parts, then hold firmly for 3O to 5O seconds.

Using Accelerators (Hot Shot, Zip Kicker). Hot shot is used for speeding things up and to eliminate problems with cold working temperatures, bonding pitchy woods or unusual materials. Use Hot Shot with any of the three types of super glues. Important: these accelerators, when sprayed on a surface or object, dries instantly and leaves no visible residue. Once sprayed, the surface is active for about five minutes without re-spraying. Don't try to keep the area wet by over spraying. Hot Shot works best when dry. A light spray covering the entire area is all that is necessary. If you do not bond the parts within the respective on-part life span, re-spray the parts.

Combinations.

Hot Stuff with Hot Shot. For small parts, spray Hot Shot on one part, assemble parts and apply Hot Stuff to the crack or joint. For large bond areas, assemble parts first, then apply Hot Stuff to all sides, then spray Hot Shot on the crack or joint where Hot Stuff was applied and wherever Hot Stuff appears along the edges. If a drip runs down the outside of the parts you can stop it in its tracks with a light spray of Hot Shot. The drip can be easily sanded away later. Hot Stuff cures quickly used by itself, but when used with Hot Shot its really fast, so keep in mind that penetration is lessened as cure speed gets faster. If for instance, a large area is sprayed before assembly, the parts assembled and Hot Stuff applied, its very likely that cure would take place before full penetration. This would leave unbonded areas inside the joint reducing it's strength. Large areas are best bonded using Super T. Lastly, NEVER apply Hot Stuff to a surface which has been sprayed with Hot Shot. Curing would start too quickly for a good bond to be made.

Super T or Special T with Hot Shot. First check the fit of the parts to be bonded to see that they line-up as you desire. This is important because bonding time is reduced. Spray Hot Shot on one part and set aside. Apply Super T to the other part in a spiral pattern. The more porous the material, the tighter the pattern should be used as some "soaking-in" may occur. Assemble and align parts then hold firmly for ten seconds (twenty seconds for Special T). For extra strength fillets, Super T may be added to the bond edges. Just run a bead along the edge and spray lightly with Hot Shot. This can be repeated until the desired fillet thickness is obtained. As with Hot Stuff, never apply Super T to an area which has been sprayed with Hot Shot. Curing would start to quickly for a good bond to be made.

Important Safety Information

Although super glues are non toxic, always use with plenty of ventilation. Cyanoacrylate fumes can be irritating to mucous membranes and can cause temporary weeping. Fresh air relieves these effects. Those with respiratory ailments or acute sensitivity to any chemicals are advised to use a respirator mask which eliminates or reduces inhalation of fumes. Such masks are available from industrial safety equipment suppliers. Always wear eye protection when working with any chemical.

Trouble Shooting Super Glue

Example: Too much Adhesive for a given bond area. Hot Stuff is used for this example, since it is the fastest curing.

The Bonding: Two cubes, each measuring 1/2" x 1/2", are placed together, Hot Stuff is applied to the bond or joint line where the parts meet. Note that the glue disappears into the joint almost as fast as it is applied and may drip out of the bottom of the joint, if application is continued.

The Result: Cure time is increased from 3-1O seconds to several minutes or longer. When curing time is extended to this degree the natural impression, is simply, the glue won't set. Note: this result is also a symptom of trying to use Hot Stuff in the same way the gap filling types are used. That is, applying glue to one part before assembly. Always assemble parts first then apply Hot Stuff.

The Problem: What is actually happening is that too much glue has been applied for this size job. The glue is being soaked up by the material being bonded, beyond its ability to hold any more. In effect, instead of a thin joint bond, this example would be an attempt to make a solid block of Hot Stuff.

The Solutions:

 

  1. Apply small amounts of Hot Stuff (one drop), to each of the four sides and hold firmly for 3-1O seconds.
  2. If the material is very porous like cork, for instance, spray both parts with Hot Shot accelerator before assembly. Then proceed as in #1 above. Note: Either of the gap filling glues, Super T or Special T, would be the better choices for a very porous material.
  3. Spray Hot Shot accelerator directly on the wet glue after bonding. Note: Hot Stuff should be applied sparingly. To make this easier, avoid cutting off more spout that necessary to obtain a small hole. For Hot Stuff, trim the spout to a 1/32" diameter hole, or smaller.

Super Glue Shelf Life

All cyanoacrylates have a shelf life which vary with the quantity in the container as follows:

1/4 ounce - six months
1/2 ounce - 9 months
1 ounce - 12 months
2 ounces - 1 year +
4 ounces - 2 years +

For long periods of storage, place unopened bottles in the freezer at or below 32 degrees. You can expect room temperature shelf life to double. It is very important to remember that this applies only to bottles which have never been opened. Always allow the bottle to come to room temperature before opening. Store used bottles at room temperature. This is because used bottles contain air from your workroom and that air contains moisture. When cooled, moisture condenses to water reducing shelf life. Always keep bottles upright when not in use.

As this life expectancy passes, the adhesive begins to progressively thicken in the bottle until, eventually, it hardens completely. For a given material, (cure rate varies slightly for different substrata), and depending on the age of the adhesive, cure time may be extended anywhere from a few seconds to twenty times normal. Bond strength is affected to some degree with the passing of normal shelf life, but, in the vast majority of cases, this is not a serious concern. Most substrata do not approach the strength of the adhesive bond. To illustrate: A decrease in strength from 5OOO P.S.I. (Strength during normal shelf life), to 3OOO P.S.I., (Past normal shelf life), represents a strength loss of over 25%. If the task is to bond a substrata, such as wood, rubber, plastic etc., then 3OOO P.S.I. is far greater bond strength than is actually needed. Under stress these substrata will almost always fail first leaving the bond intact.

Even if shelf life has passed, any of the super glues are usable as long as they remain liquid.