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.
- Polyvinyl acetate (PVA or White School Glue)
- Aliphatic (Carpenters Glue, Wood Glue)
- Cyanoacrylate (CA Glue, Super Glue, Krazy Glue, etc.)
- Polyurethane Glue (Gorilla Glue)
- Contact Cement
- Model Airplane Glue (Testors)
- Other Glues - Research the web for additional types of glues.
Review the safety rules on the SAFETY page before using any glues.
Criteria teams should consider when selecting a glue.
- Can we use the glue safely?
- How difficult is it to use the glue?
- How long does it take for the glue to set?
- How strong is the joint created by the glue?
- How much weight does the glue add to the structure?
(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
- Always read and follow manufacturer's use and safety instructions.
- Air is the enemy of most glues. Keep glue bottles covered when they are not being used.
- MORE is not better!. Too much glue can create a weaker joint than not-enough glue.
- All glues work best when you maximize the contact area between the surfaces being glued. Remove any burrs or roughness before gluing surfaces together to insure the maximum contact area.
- Generally glues cannot be used as a coating and the challenges have started defining how much glue can extend past a joint. Refer to the challenge specifications for specifics.
- It is generally a bad idea to mix glues. There is no way to predict what will happen when two different glues are mixed. This is not to say that a structure cannot be built using a variety of glues. A team may discover that certain glues work best for certain situations.
- It is NOT a good idea to use any of the solvents or materials listed for cleanup on your structure. You can weaken the joints.
- Glues should be kept out of direct sunlight.
- Certain glues degrade when exposed to heat.
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.