Plastic trim repair

[Dale C.]

What is the best way , ie strongest way, to repair plastic trim items that are cracked or even need building up a small missing piece? Dale

[Dale C.]

Re: Plastic trim repair

Never mind, I just found my old thread "a Glue that holds".


https://www.forums.ncrs.org/showthre...holds&p=471932

[Paul J.]

Re: Plastic trim repair

Dale, if the thread does'nt say this, reinforce the back of the piece behind the crack with a piece of plastic, if you have enough room.

Paul

[Dan B.]

Re: Plastic trim repair

Dale,

JB Weld has a newer 2 part epoxy product specifically formulated for plastic repairs. It's VERY strong and can be built up and shaped after it cures. I have had good results using it. Dan

[Richard M.]

Re: Plastic trim repair

My first choice to repair most plastic items.........

Cyanoacrylate(super glue) an baking soda. Use the cheap thin super glue in the tiny metal squeeze tubes. Don't use the high build thicker type. I've been doing for many years after learning the trick when I was building RC model airplanes long ago, using it to strengthen frame joints at their corners.

I also use it to fill open cracks. Sprinkle the baking soda into the crack or missing piece. Carefully drip the super glue onto the baking soda so it soaks in. As the baking soda and super glue react, there may be heat and a bit of vapor and smoke. It's the chemical reaction. Protect your eyes. The soda is the agent to cure the glue with absence of air. It may take several applications to fill larger voids. If the backside of the crack is hidden, you can build up the backside with a small amount of the soda surrounding the crack. Drip the super glue around it and you've created a filler for extra strength. You'll be amazed with the results on most plastics.

I recently rebuilt a generator and the plastic insulator for the Field terminal was cracked. I used the SG & BS to repair it.

Here's the insulator when I disassembled the generator. The nut was seized on the stud and the insulator broke when I took it apart. I think it was cracked before under stress and I made it worse.
.__480_360_P9030003.JPG


Here it is after the repair. You can see the repaired area at 4:00. There was a large void on the inside I also filled.
P9040019.jpg

It went back together fine and the stud held firmly and properly insulated. I motored the generator and it worked fine. Full rebuild info here.
.__480_360_P9050061.JPG .__480_360_P9060079.JPG

I've used this type of repair on many items in the past. The most memorable one was when a relative was leaving my house and traveling home on a long ride many years ago. It was raining. The windshield wiper shaft housing on the wiper motor was broken and the wipers were not working right . All shops were closed and she had to get home. I used my super glue/baking soda trick to do the repair on the piece. She made it all the way home and that repair lasted a long time. We joke about it to this day. She still can't believe I was able to fix it.

Rich

[Lawrence S.]

Re: Plastic trim repair

Richard that's a great tip thanks.

[Lawrence S.]

Re: Plastic trim repair

Will the baking soda and super glue work on a radiator shroud?

[Richard M.]

Re: Plastic trim repair

Will the baking soda and super glue work on a radiator shroud?

Lawrence, It depends on what type of plastic, or is it actually fiberglass? If FG I'd use FG mat/resin or chopped mat to fill grooved out cracks. If truly plastic, the shroud may be subjected to stress so you might want to consider that plastic epoxy mentioned above. I'll have to get some of that and experiment some day. If it's just cosmetic the super glue/soda trick may work. There are particular plastics that don't allow that process to adhere. I've found ABS is one. Plastic welding is the only way I think, but that's a completely different process and cost.

I've had repairs that held very well. Some haven't. For those that did not, the bond came apart easily and cleaned up so I could try other adhesives.

Your best bet is try the SG/BS process and see if it works. Again, just use caution when dripping the glue over the soda. Don't plant your eyes directly above the repair. Large areas require much liquid and can be built up. I use a xacto blade as a trowel to apply the soda, a little at a time over the repair. Then drip the SG on. I get more soda on there and repeat the build up. For a last layer I sometimes drip glue over the hardened repair and quickly sprinkle soda over the area for a final build. The beauty of this process is that it's a "instant" repair. No need to wait for curing/drying time.

Rich

[Patrick N.]

Re: Plastic trim repair

There are particular plastics that don't allow that process to adhere. I've found ABS is one. Plastic welding is the only way I think, but that's a completely different process and cost. Rich

Exactly: Super glue is very crystalline and brittle by nature and does not hold up to excessive exposure to high temp. Not a good long term solution. Baking soda as an accelerator is a replacement for your skin- (cyanoacrylate (CA) glue was a failed WWII medical "Stitch" to stop bleeding on the battle field and is why it bonds so fast on your skin. Acetone / nail polish remover will break the bond of any CA bond - now you know, ). If you do use CA, a more effective accelerator is "Zip Kicker". If you need to "fill gaps" you can also buy a variety of CA consistencies from very thin to very heavy.


ABS is used as the substrate on the dash and console. if these are broken you can create a backer plate to locate under the repair area with another thin piece of sheet ABS or polystyrene (ABS is a Styrene based so styrene would work) To bond, use REZ-N-BOND, it is formulated for styrene-based plastic adhesion. It is very thin and the capillary action lets the agent wick quickly and creates a superior bond. Not to get too technical but this system creates a chemical cross-link of the styrene molecules for a permanent bond.

[Patrick N.]

Re: Plastic trim repair

PS- a great trick to create a thick ABS repair material: fill a glass jar with some REZ-N-BOND and add a bunch of cut up strips of ABS, close the jar and let that dissolve for a few days, keep adding strips until it is sludge-like. You can use this sludge to fill large gaps. Once dry it is very strong and fills the gaps nicely.