Glues and Adhesives

Most structure challenges allow the use of any type of adhesive. However, it is important that teams read the challenge and make sure that there are no restrictions on the types of adhesives that can be used. This page deals primarily with products that fit under the generally accepted definition of glue. Sometimes the challenge may have a very loose definition of what is allowed to be used as glue or adhesives. Teams should take this as an opportunity to research alternate "glue-like" products that are not covered under this topic.

It is not interference for the Team Manager to tell a team they cannot use a glue if the Team Manager does not believe the team can use the glue safely. It is not interference for the Team Manager to purchase a variety of glues for the team to experiment with and to teach them how to use them properly. However, the team must make the choice about the glue or glues that they wish to use for their structure.

Gluing two pieces of wood together may not seem like a big deal. But there are many different glues and adhesives that teams can choose from and that they must then learn to use correctly. Experienced builders try to glue their structure together so the joints are consistently strong without using too much glue.

All glues require that application of some amount of pressure to set properly. Refer to the manufacture's recommendations for the amount and length of time pressure should be applied. It is also important that the process used to apply pressure to the glue joint does not apply extra stress to the materials so that they are weakened by the gluing process.

The following is a list of different types of glues. This list is not all-inclusive. You can find additional glues that are available by visiting a local home improvement center, hobby shop and by doing searches on-line. Click on the links below for additional information about the glues listed. Brand names are listed for reference only and are not meant to imply that this is the only (or best) product to use in any particular category.

Select a link at the bottom of the page for more information on specific adhesives.

Review the safety rules on the SAFETY page before using any glues.

Criteria teams should consider when selecting a glue.

(Teams may also want to devise tests to determine the answers to these questions.) Plans for a glue joint testing device are available from the Specialized Balsa Wood website listed on the links page.

This is by no means a complete list of all the criteria teams should consider when selecting a glue or glues. Teams should come up with their own glue selection criteria.

General Rules for Gluing

Is there a best glue to use?

There are structure teams that "know" that they are using the best glue for their structures. While certain glues work best in different conditions my personal observation is that it is not so much the particular glue that a team uses - it is how the team uses the glue they have chosen. Most glues will form a bond that is stronger than the wood that is being glued. Examine structures that you have tested paying particular attention to the glue joints. If the joints tore and there are shreds of surface "A" clinging to surface "B" then you have probably used the glue correctly. This demonstrates that the glue joint was stronger than the materials being glued. If, however, the joint broke "clean" and there is no tear out of one surface then you may not be using the glue correctly. If this continues to occur then the glue you have selected may not be the best glue for this particular application.

More than you want to know

The terms glue and adhesive are often used interchangeably. Technically "glue" is a natural adhesive made by "boiling collagenous animal parts into hard gelatin and then adding water." Adhesives include glues and any synthetic material capable of creating a bond between two materials.

Polyvinyl Acetate Glue

(PVA for short) is the white glue typically sold for school use.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Pros

  • Very safe.
  • Non-toxic.
  • Easy to clean up.
  • Bonds in about one hour.

Cons

  • It is not waterproof
  • Not specifically designed for wood

Cleanup

  • Cleanup with damp cloth.
  • Remove from skin with soap and warm water.

How to Use

Apply a small amount of glue to wax paper (about the size of an aspirin or dime). Use a toothpick to apply a drop (or several drops depending on the size of the piece being glued) on one surface. Place pieces together and hold under pressure per manufacturer's recommendation. Refer to aliphatic glue page for pictures. The procedure is the same. Once the glue on the wax paper starts to film over the glue should not be used.

Aliphatic Glues

Aliphatic glues are also referred to as wood glues and include glues such as Elmers Wood Glue and Titebond.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Pros

  • Non-toxic.
  • Joints are slightly flexible.
  • Easy Cleanup.

Cons

  • Joints must be clamped or held under pressure for at least 30 minutes.
  • Joints are slightly flexible.

Cleanup

  • A damp cloth can remove glue that has not dried.
  • Clean hands with warm soap and water

How to use

It does not take a lot of Wood glue to make a good joint. In fact, too much glue will create a weak joint. The tips with most wood glues do not allow fine control of the amount of glue being dispensed. One method for applying wood glues is to place a small dab of wood glue (about the size of an aspirin or possibly a dime) onto a piece of wax paper and then use a toothpick to pickup small amounts of glue (Photo 1). Then use the toothpick to transfer glue to the structure. (Photo 2). Then apply pressure to the joint per the manufacturer's use instructions. You can use a small weight (Photo 3) or a book to apply pressure. You can also use hat pins (Photo 4) to maintain pressure on the joint. When the glue on the wax paper starts to film over (may take from 10 to 20 minutes) it is no longer useable and should be discarded and replaced with fresh glue.

Photo 1
Photo 2
Photo 3
Photo 4

 

Cyanoacrylate

Cyanoacrylates (CA glues for short) include glues such as Jet, Super Glue and Krazy Glue.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Pros

  • Sold in various viscosities with set times from 1 second to 1 minute allowing very quick assembly.
  • Generally non-toxic (but that doesn't mean you should eat it)

Cons

  • CA glues give off fumes while setting that can irritate the eyes (wear goggles and work in a well ventilated area)
  • CA glues give off heat while setting which can lead to minor burns on the skin.
  • Typically has a very quick set time once it is put under pressure and thus is not very forgiving of mistakes during assembly.
  • Does not fill gaps very well although certain of the slower setting CA glues will fill some gaps.
  • Does not work well for end-joint connections.

Cleanup

  • Most CA manufactures sell a De-bonder for cleanup and removal of CA glues.
  • Most De-bonders are acetone which can be purchased in quart containers at hardware stores. Fingernail polish remover will also work.

How to use

  • When cutting the tip off CA glues for the first time it is a good idea to remove the lid to release any pressure that may have built up in the bottle so that you do not risk the glue spraying out when the tip is cut.
  • With CA glues the closer the parts fit together the stronger the bond.
  • CA glues work best in a thin layer between smooth surfaces so any rough spots on the mating surfaces should be smoothed before gluing.
  • Do not touch the tip to the surface being glued.
  • Most places that sell CA glues also sell Teflon tubing and/or extender tips which can aid in controlling the amount of glue that is dispensed.
  • Medium viscosity (5-15 second bond time) and heavy viscosity (20-60 sec bond time) CA glues are used in the same way. Place a small dot (or dots depending on the area being glues) on one surface. Then carefully place the pieces together (you probably will not get a second chance) and hold them under pressure for the manufacturer's recommended time. (see photo below)
  • Practice using small dots of glue to glue pieces together. Experiment using more or fewer dots of glue to determine the optimum amount of glue to use for each type of joint.
  • Very thin viscosity (1-3 second bond time) CA glues are used differently. Place the pieces you wish to glue together and then carefully drop the glue onto the joint. These glues are so "thin" that they wick into the joint creating an almost instantaneous bond. Be very careful because it is very easy to glue your fingers to the materials.

Other Notes

  • While CA glues set very quickly they do not reach full strength for several hours. Refer to instructions included with the glues. Allow for this before subjecting to maximum stress.
  • CA glues should be kept in a cool place out of direct sunlight.
  • CA glues typically have a shelf life of from 12 to 24 months.
  • Unopened bottles of CA glue can be stored in the refrigerator to prolong shelf life but should be warmed to room temperature before using.
  • Always buy a few extra tips when purchasing CA glues. If manufactures instructions for cleaning up after each use aren't followed it is very possible that a glue tip may become unusable until it is soaked in acetone to remove the glue that has setup in the tip.
  • Buy several extra tips. When you finish using a tip, store it into a small medicine bottle (the type with a water tight lid) filled with acetone and let it soak. If you do this make sure you remove the tip from the acetone and let it dry thoroughly before using.

  Interesting Fact

CA glues are sometimes used to suture wounds and to graft skin, bone and cartilage. However, if you happen to graft your skin to the structure you are constructing you should remove it so that you aren't cited for using a material on the structure that is not allowed in the challenge. ☺
 

Epoxy Adhesive

There are many brands of Epoxy Glues. Elmer's sells a product called Elmer's Probond Epoxy Glue. Epoxy glues are sold as two components that must be mixed to be used.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Safety

  • Use in well ventilated area.
  • Keep from contact with skin.
  • Work in well ventilated area.
  • Keep away from flames and sparks.

Pros

  • Water resistant
  • Solvent resistant
  • Fills gaps
  • Bonding times vary from very quick to 24 hours.

Cons

  • Some epoxies are toxic (varies by brand and product)
  • Once the two components are mixed there is a limited time that the glue is useable.
  • Some epoxies are flammable (varies by brand and product)
  • Relatively expensive when compared to other glues.

Cleanup

  • Remove dried glue from hands and work surfaces with Acetone. Wash hands with soap and water after cleaning with acetone.

How to use

Every epoxy glue has its own requirements but generally equal parts of the two components are mixed on a piece of wax paper. Use a toothpick to apply glue to joints. Follow manufactures recommendations for open work time, clamp time and bonding time. The same technique shown in the pictures on the Aliphatic glue page can be used for Epoxy glues.

 

Polyurethane Adhesives

Polyurethane Glues include glues such as Gorilla Glue, Elmer's Ultimate Glue Polyurethane and Titebond Polyurethane Liquid Glue. Polyurethane glues were designed specifically for wood but may work well on other materials as well.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Safety

  • Work in well ventilated area
  • Keep acetone or denatured alcohol on hand for cleanup from hands
  • Keep from contact with skin.
  • Wear goggles

Pros

  • It is solvent free.
  • It is waterproof.
  • It has a twenty minute open working time which gives time to get things positioned properly and clamps or other holding mechanisms in place.
  • Because of its expansive properties it tends to work better than most glues for end-grain joints.
  • Slightly elastic.
  • It expands and gets "into" the wood as it sets so creates a very strong joint.

Cons

  • It is toxic to touch and ingest.
  • One surface must be slightly moistened for the glue to set. Polyurethane glues expand with moisture and can be extremely messy if not used carefully.
  • Polyurethane glues require pressure to adhere and so joints must be kept under pressure until the glue has set. Set time can run as long as 4 hours during which the joint must be kept under pressure.
  • More expensive when compared to other glue options.
  • It expands and foams as it sets so if used incorrectly can spill out beyond the allowable limits for a glue joint.
  • Slightly elastic.
  • Difficult to remove from hands once it dries.

Cleanup

  • Denatured Alcohol or other solvents will cleanup polyurethane glues.
  • Acetone will also work for cleanup.

Instructions for use

Each manufacturer's instructions for use are slightly different. These instructions are included for reference only. It takes very little polyurethane glue to make a strong joint. After the surfaces to be glued have been smoothed, take a damp (not wet) cloth and lighted dampen one of the surfaces being glued. Next spread a very small amount of the polyurethane glue on the other surface. A good way to spread the glue is to use an old credit card and holding one of the long ends hold light pressure on the card as you drag it across the glue to create a thin sheen of glue on the surface. Mate the two pieces together and apply pressure in accordance with the manufacture's recommendation - usually 2 to 4 hours.

It is very easy to use too much of a polyurethane glue so you may want to practice on scrap pieces of wood until you get a feel for the correct amount of glue to apply. Click on the link on the right to see an example of what happens when you have too much glue in the joint. You can see that the glue has foamed out beyond what is generally allowable under structure challenge specifications. It is very difficult to remove this foam without damaging the underlying surface.

Because these glues expand it is very important that the surface you are building on be non-porous. Otherwise, the glue from the joint may expand into the surface underneath and you will find your structure glued to the work surface. I have had the glue grip onto a plastic laminate surface I was working on and tear off a piece of the laminate when I picked up the structure. Taping a piece of wide clear shipping tape to the surface under the joint prevents this from happening.

These instructions are from my experience using Gorilla glue. As I browed websites looking for information on glues I noticed that some manufacturer's have a polyurethane glue that may not require moistening of one surface.

Contact Cement

Contact cement includes glues such as DAP Weldwood. Used in the construction industry for joining plastic laminate to counter tops.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Safety

  • Use in well ventilated area.
  • Keep away from heat, sparks and open flames.

Pros

  • Long open time (up to 2 hours) with short (almost instant) set time

Cons

  • Very Toxic - Inhaling vapors can be harmful or fatal.
  • Vapors and liquid are extremely flammable.
  • Can be very messy.
  • Very difficult to adjust pieces once put into place.

Cleanup

  • Remove from skin with acetone and then wash with soap and water.
  • Remove from work surfaces with acetone.

How to use

  • Apply thin layer to both surfaces and allow to dry until glossy. Typically at least 15 minutes up to two hours.
  • Press parts together.

 

Model Cement

Model cement is sold by many suppliers but the most commonly known is Testor's Wood Cement. Note that Testor's and other manufacturer's sell many different types of model cement - some intended for use with plastic and some intended for use with wood. Read the labels before purchasing.

The information provided is general. Always refer to the use, safety and cleanup instructions included with the glue.

Safety

  • Avoid breathing vapors
  • Work in well ventilated area.
  • Avoid contact with eyes and skin.
  • Wear goggles.
  • In case of eye contact, flush eyes immediately with water and seek medical attention.
  • Vapors may cause a flash fire if exposed to open flames or sparks.

Pros

  • Designed specifically for small model construction.
  • Relatively quick initial set time allows rapid assembly of structure although full bonding does not take place for at least twelve hours.

Cons

  • Toxic.
  • Fumes are dangerous if used in an enclosed area. Use only in a well ventilated area.
  • There is a reason that this glue is kept behind the counter at hobby stores.
  • Highly flammable.

Cleanup

  • Remove dried glue from hands and work surfaces with Acetone. Wash hands with soap and water after cleaning with acetone.

How to use

Use in a well ventilated area away from open flames and sparks. The tips of model cement are generally small enough to control the amount dispensed. However, you may find it easier to dispense a small amount on a piece of wax paper and then use a toothpick to apply the glue. Apply a small amount of glue to each surface to be glued. Allow to dry for a few seconds, press together and allow twelve hours for full bonding of wood. Pictures on the Aliphatic Glue page illustrate this technique.