super glue

[stuo]

Does anyone know why super glue sometimes just won't work? Recently I used it successfully on the plastic muffler cover on my DT300 yet it didn't work on the crack in the air filter box, which looks to be the same type of plastic. Does the stuff go bad once you open the tube? Is there some trick I need to know? Help!

[CROSSBOLT]

It is kinda like rear view mirrors cannot be super glued to glass. There is a limit to what most any kinds of glue will actually bond. Ya gotta read the fine print and even then you cannot be sure. I think the heat shield's are thermo setting  while the airbox is thermo plastic meaning the shield will not melt with heat where thermo will. Thermo can be "welded" with a heat gun and filler rod. All this will not fix your problem! Superglue DOES lose its effectiveness once opened so you may as well throw the tube away once you have stuck all your fingers together. JB Weld and Gorilla Glue stick to nearly everything but the Gorilla needs water to activate. JB is a two-part epoxy. You may have to experiment to find out what works unless someone here has used something successfully. 'Cours you knew that! Hang tight, someone will answer.

Karl

[eamartin]

I think the heat shield's are thermo setting  while the airbox is thermo plastic meaning the shield will not melt with heat where thermo will. Thermo can be "welded" with a heat gun and filler rod.

This is probably the answer although I'm not familiar with the DT300.  In a previous life I had to deal with adhesion to various plastics (adhesives, primers and paints).  Generally the color-impregnated plastics (polyethylene and polypropylene) could not be adhered to simply because during the manufacturing process the mold release agent was a part of the mix.  Unlike fiberglass layup, after production in addition to the mold release agent on the surface of the cured part, there was mold release agent throughout the plastic.  Unfortunately, one could clean it off the surface, but with time and exposure to heat /sun, some of the agent would migrate to the surface and reject the adhesive, primer or paint.

[ole two wheels]

I once ripped a nice gash in a 40 gallon holding tank on my motor home while doing a little off roading.I got on the PC and came up with this repair. I dried the bottom side of the tank and scribed  a border around the damaged area and lightly roughed it with sandpaper. Then using 30 minute epoxy and a 2" chip brush, I coated the whole area. I cut a piece of silk to fit and after the glue had gotten tacky I pressed the silk into it, using rubber gloves. Then I allow this process the full cure time. Then I emptied the double chambered epoxy tube onto a paper plate and mixed it well with a popsicle stick and brushed on another coat. Sounds like a lot of work, but not really. Any job worth doing, is worth doing right. I had a gash about 6 inches long that I could stick my pinky thru. 40 gallons is a lot of weight and she never leaked. Considering that , that type of plastic was just one molecule away from being margarine, that was a very good repair.

[stuo]

Thanks, gents, for the rapid and detailed responses. I spoze I'll have to find a way to hold the cracked parts together until the "quick" epoxy sets. Five minutes is a looong time when trying to hold something motionless.

Stu

[stuo]

P.S. I bought a Loctite two-part super glue for plastic from ebay and it worked well enough for me to squeeze some epoxy into the remaining cracks for back up strength. Sloppy looking, but strong enough.

Stu

[Mr. Paul]

I have never had a good repair with Super Glue. It seems like it sets too quickly, fills only the tightest of gaps, and is too inflexible for use with any vibration. JB Weld is the product I use the most and with the most success. I love the stuff.

[stuo]

I agree with you 100% on JB Weld, Mr. Paul, but edge-glueing cracked plastic required instant grip because I don't have the stamina to hold it motionless for five minutes, nor could I clamp it due to its shape.

I did find a two part super glue made by Loctite specifically for plastic that worked about 50%, and I filled in the cracks with JB. It worked! 

[Mr. Paul]

I agree with you 100% on JB Weld, Mr. Paul, but edge-glueing cracked plastic required instant grip because I don't have the stamina to hold it motionless for five minutes, nor could I clamp it due to its shape.

I did find a two part super glue made by Loctite specifically for plastic that worked about 50%, and I filled in the cracks with JB. It worked!

Brilliant Stuo! I will keep that trick in mind!