There are hundreds of glues on the market. Which type of glue do you use? And which brand?
In this blog entry I’m going to deal with which glue is best to use with STYROFOAM, more formally known as EXTRUDED POLYSTYRENE FOAM (XPS) or CLOSED CELL POLYSTYRENE. This kind of styrofoam is used in crafts and model building. It is the white styrofoam you find electronics (such as TV’s, DVD players, cell phones, etc.) packaged inside before they are put in the box. It is also very popular for building remote control (RC) airplanes.
And for the RC plane enthusiasts, what do you use to repair your plane when it breaks?
Here is my experience and recommendation for use with STYROFOAM for model building and repairs, such as radio controlled airplanes. In future blogs I’ll describe the main types of glues for other materials and give you my recommendations. Now, all about STYROFOAM glue.
I have a couple RC planes made of XPS foam. What do you do if you crash and break a wing in half, or even the fuselage? Well, I've broke both. Actually, “broke” may be an understatement. The fuselage snapped in half right through the cockpit, leaving the airplane in two separate pieces! I broke the tail section clean off. I snapped a wing two and broke off and broke in half an aileron.
Now, most would think that was the end of it and I’d have to buy a new fuselage or new wing. Not so. With the right glue you can normally repair to “better than new” condition. Normally, the fear and the problem with any repair in any material is that the repaired joint will be weaker than the original material and will not stand up to abuse, let alone regular use, like the original unbroken material. Well, I figured that there was no harm in trying to repair it - just a few dollars on some glue and some of my time, and I’d spend more time and money buying a replacement fuselage and rebuilding my plane.
Based on my experience with glue, my guess was the right glue would be a polyurethane glue. I also called my local hobby store where I bought my plane. These guys are model building experts, so they should know what glue would work, if at all. They recommended a product called “Ultimate RC Foam Glue“, by Yard Bird (www.yardbirdrc.com). It sells for $14.50 per bottle. So, I bought a bottle. Online recommendations included using a typical craft / hobby hot glue gun with wax glue sticks.
But, I didn’t want to just go ahead and glue up my airplane and hope it worked. So I decided to perform a little test first.
I took 4 pieces of the styrofoam that my speakers had come packaged in. I broke each of these in half and then glued them back together as follows:
1) The first piece I glued back together using “Gorilla” polyurethane glue. I spread a thin but even coat on one of the pieces then sprayed water on the other piece with a spray bottle mister. I pressed the pieces together and then clamped them gently in a vice grip. (Polyurethane glue expands greatly as it cures, pushing the pieces apart; so you need to clamp them to keep the pieces together.)
2 & 3) The next two pieces I glued with the “Ultimate RC Foam Glue“. It is very easy to use. Spread a thin but even coat on one piece. Press the pieces gently together and immediately separate. Then press together a second time and separate a second time. Then press together and hold for 60 seconds and then set aside to dry. (On one test piece, I pressed together and separated only once; the second test piece I performed the “press and separate” twice as per the product instructions.
4) The final piece I glued with a hot glue gun. I used the clear general purpose wax glue sticks.
The next morning after about 12 hours of drying time, I took my first three repaired test pieces and tried to break them in half again. RESULTS:
1) The piece glued with the Gorilla glue eventually broke BUT in a different spot than the original break. So the glued joint was as strong or stronger than the original unbroken material. As good as new!
2 & 3) The two pieces glued with the “Ultimate RC Foam Glue“ glue held up very well, but when the piece broke, it broke along the exact joint of the repair. So, the joint was the weak point in the material and thus was weaker than the unbroken material. (NOTE: I judged both pieces glued with the Ultimate RC Foam Glue to hold up about the same, so it didn’t seem to matter whether I pressed and seperated once or twice when I was gluing the parts.)
4) I waited 1 hour after the repair and then tried to break the piece in half. The piece eventually broke but in a different spot than the original break. I kept trying to break the repair along the original break joint, but it ALWAYS broke in a new spot. Then I tried to pry the repaired pieces apart along the glue joint but COULD NOT. The repair was stronger than the original material.
CONCLUSION: For the ultimate strength and easy of use, use a hot glue gun. It is easy, dries fast and the repaired piece is stronger than the original material! A hot glue gun will have a beak of squeeze out along the joint. Just break this bead off with your fingers, or trim with a razor blade, and your repair joint is invisible.
When I first broke my tail section on my plane, I repaired it with gorilla polyurethane glue and “clamped” the two pieces together with gorilla tape. The repair was excellent. In this photo you can see the "tan coloured" polyurethane glue repair line.
A few days later after repairing my tail section, the tail section broke again in a crash. But it broke in a different spot than the first repair, proving the original repaired joint with the gorilla glue was at least as strong as the original undamaged material. In both the following photos you an see the original tan glue line from the first repair - the new break is in a different spot.
This second time, I repaired the break with a hot glue gun. 12 minutes after the crash, I had plugged in my glue gun, made the repair and was back up in the air flying! You cannot perform a repair and be using the model that quickly with any other glue. Polyurethane will provide a strong repair, but it takes many hours of drying time and you need to clamp the pieces together with some tape. A hot glue repair is done and ready to use in less than 15 minutes.
REPAIRING WITH GORILLA GLUE
You can also use a polyurethane glue, but it is not as easy to use. It expands and leaves a messy joint once dry, but this is easily cleaned up by using a razer blade to cut the glue off the styrofoam - very easy to do. Also, it dries beige or cream. And, you need to clamp the joint while it dries.
To repair my airplane fuselage, I glued the pieces with the Gorilla glue and then “clamped them” by putting “Gorilla Tape” across the joint: press the joint firmly together, then stretch a piece of Gorilla tape across the joint on either side of the fuselage to help draw and keep the joint together. The tape comes off cleanly and easily. 12 hours later the joint is as good as new!
Since repairing my snapped fuselage, the airplane has been flown many times, had many crashes and the joint shows no sign of failure. My first flight was about 12 hours after the repair. My first crash 12.5 minutes after the repair. And still going strong.
REPAIRING WITH HOT GLUE GUN
To repair my tail section and my broken wing, I applied a bead of hot glue along the edge of the broken section. Then I covered the entire surface with hot glue. Press the two pieces firmly together and hold together for 60 seconds. The glue will squeeze out forming a bead along the entire length of the joint on both sides. In 15 minutes the glue will be hard and dry. Simply use your thumb to break the glue bead off the foam, or use a razor blade to trim the glue bead, leaving an invisible joint. For repairing the thin broken aileron in the below photo, after glueing the two halves together with hot glue, I then used clear duck tape to cover the full length of both sides of the aileron to give it extra strength and rigidity.
Now the hot glue only works on Styrofoam to Styrofoam. If you are trying to glue a plastic or metal part to some styrofoam, the hot glue will bond permanently to the sytrofoam, but the plastic or metal part will come loose easily from the hot glue. So, if you want to bond other materials to the styrofoam, you will need to use polyurethane glue. An example is the plastic motor mount. When it broke on my plane, I needed to glue it back onto the styrofoam fuselage. Hot glue broke off easily. Using polyurethan glue, the plastic motor mound bonded permanently to the styrofoam.
REPAIRING WITH "ULTIMATE RC FOAM GLUE"
The “Ultimate RC Foam Glue“ is easier to use than polyurethane glue and it dries clear with no mess to clean up afterward. This glue is great for putting foam pieces together for crafts and non-structural/ non-stress bearing repairs to model airplanes. And it cures faster than the polyurethane glue. However, if it is going to be a major structural part and endure stress, use the hot glue gun or Gorilla glue. And compared to Gorilla glue and Hot Glue sticks, the Ultimate RC Foam Glue is expensive.
POLYURETHANE GLUE SUMMARY
You definately need some of this glue around your house.
- It is awesome for just about any materials including styrofoam
- has very little odour
- bonds to skin
- requires water to activate it
- expands as it cures, so requires clamping to hold the pieces firmly together while the glue cures
- “squeeze out” from the expanding glue can be cut or sanded after dry (or wiped off while wet)
- expensive compared to regular craft and wood working glues, so only use for special situations where normal glues will not work
HOT GLUE GUN SUMMARY
- no odour
- does not bond to skin
- is normally only used in crafts or for a “non permanent” or temporary glue solution for most materials
- is the ULTIMATE glue for styrofoam
- fast, easy, invisible repair
- bonds permanently ONLY TO STYROFOAM - all other materials is a weak, temporary bond
ULTIMATE RC GLUE SUMMARY
- strong fumes / odour
- bonds only to styrofoam
- easy to use with little or no mess
- invisible joint line