From the UHU.com website:
UHU por is a quick-setting special adhesive for bonding expanded polysterene, e.g. Styropor® also in combination with other materials. It forms an elastic adhesive film which is highly resistant to age, colorless and waterproof.
UHU is a German company. As best as I can tell, at least some of the UHU Por is made in China. The Bolton Group who owns UHU also owns Bostik USA which is well known for their construction and industrial adhesives. There must be a good reason why UHU Por isn't sold in US Retailers. I am free to speculate. My best guess is that when you're dealing with large, multinational corporations, ones that are conglomerates that acquire other corporations people get very defensive. These corporations are usually run as independent companies. They have their own product lines in their established markets and don't want to be told what to sell by the bean counters who put these large conglomerate deals together. They also object if a corporation under the same conglomerate umbrella turns into competitors in their established markets. It's more likely a turf war more than any harmful chemicals in the glue that keeps it from being stocked in distribution in the United States. If you buy it, it will ship from out of the country. My last purchase was from Amazon, it arrived in a week.
Look out for a good deal.
When I had foreign exchange students from Germany, I tried to take them to American places. Toward the end of the trip I decided to show them WalMart. Most of the Chinese made items were available in Germany. These were teenage girls however, and they wanted to go to the Heath & Beauty section. When they found the Revlon makeup they were grabbing it off the shelf, calculating exchange rates on their phones, buying more. When they got back home they started calling their parents to send more money. Word of this wonderful place known as Walmart spread among the group and soon they were asking to go back!
So, when my trip to Germany happens I already know what I am going to do. I am going to wear my not best clothes. At the end of the trip I will throw them away. Half my luggage will be German chocolate bars, the other half will be UHU POR. I am not kidding.
Because it's sourced elsewhere it can sell for a bit more than adhesives of similar sizes in the United States. I recently bought three tubes of it and paid around $5 a tube including shipping for a 40ml tube, so it wasn't bad. You just have to be careful when looking around online, some people want way too much money for it.
A contact adhesive
The idea behind a contact adhesive is that if you're joining two pieces of foam together you need to put a bead of glue on each side, give it ten minutes until the adhesive gets a film on it, then join the pieces together. You can use an accelerator with it, I find it doesn't help all that much. Don't bother spreading it with knife to thin it out. I find that the pores in the foam seem to allow plenty of surface area for the glue to hide. In my experience, thick beads work the best.
A flexible bond
Glue is often thought of in very simple terms. All it's really about is attaching two or more things together. But, the adhesives and the bonds need to be considered. Let's compare a few.
Elmer's Glue-All - This Columbus, OH glue is world famous and a staple in many American homes. It's abundant, dirt cheap and highly effective. It applies quickly with no mixing and does provide a very strong bond with excellent tensile strength. Many foamy enthusiasts swear by it because it bonds strong, covers well, and dries clear. The downside is that it dries slowly. It can take days before it's fully dried. You can't use it for quick fixes on the field. If you goop it on too thickly it can form a layer of what looks like a think piece of plastic that can easily shatter. If you push it together too firmly you can create what is called a "starved joint." The bond will easily break.
Epoxy- Similar to fiberglass resin epoxy creates a plastic like bond that is also very strong. There is a lot of confusion as two what the different numbers mean. 5 minute epoxy means that once you mix it you have essentially five minutes to apply it before it starts to cure. 30 minutes means you have a longer period of time before it starts to cure. The end results can be quite different between the five minute, 15 and 30-minute epoxies. I prefer the 30 minute epoxy. Relatively speaking, it's fairly cheap and easy to aquire.
Epoxy does offer a very strong bond as well. Depending on where and how it's applied it can give extra support and rigidity to a foamy plane. It can also shatter with impact, and like Elmer's glue, it offers no flexibility in the joint.
When modern cars are designed they are done so with the idea that they may very will be crashed. A crash will transfer a lot of energy in a short period of time. Absorbing energy and transferring it is part of the design. If a car had a solid wall of 3-inch thick steel at the front of the car it wouldn't be safer. That solid wall would soon be what stops people in the cabin from going further during a front end collision. Ironically many bumpers on modern cars have styrofoam inside because foam helps absorb energy in low-speed crashes. What is important in a crash isn't rigidity as much a flexibility so that energy can transfer and get used up as metal, plastics and foam warps, bends and crushes during impact. The idea is to use up energy before it gets to the occupants in the cabin.
If you think of planes in similar fashion then you'll know that a hard bond isn't always the best idea when it comes to crashing a plane. A flexible bond on a flexible EPP foam wing means that the energy is transferred through the bond to other parts of the foam. What this means is that your plane may not split in half at the joints when it hits the ground.
UHU Por features a flexible bond. For certain applications this is what is preferred, such as flexible EPP foam. Though it's a contact cement I find that it takes a few days for it to fully dry. One of the main ingredients is natural rubber adhesive along with other things that allow for a good bond. Rubber cement is fairly inexpensive and provides results that are too aren't good enough to hold together foam RC airplanes. UHU Por smells like it has a CA adhesive in it as well. It's impossible to tell exactly what's inside and to what ratio. All I can say is that UHU Por simply works. It doesn't foam up like Gorilla Glue.
My rating
If money is no object and you want a very good adhesive, UHU is the best I've found for EPP foam planes. The cost and lack of easy availability drags it down a few notches in my book. I give it an overall rating of 80%. I will continue to use it though I will seek out other options.
Update- I had to remove some POR from a plane today. It didn't come off, but tore the EPP foam below it. I am so very impressed!
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| Hacker calls for UHU POR specifically for the Evo 1000 build. |
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