Do it yourself plastic repairs.

   / Do it yourself plastic repairs. #1  

alchemysa

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Oct 6, 2006
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Location
South Australia
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Kubota B1550HSD
(I first posted this on a bike forum, but I thought it may be of interest to members here who are not aware that plastic can often be repaired quite successfully and easily.)


When I got this bike both mudguards were snapped in half, one of the side panels was in three pieces, the front plate had a big chunk missing, and there were numerous other cracks around the place.

The tools are basic and cheap. You just need a soldering iron, a hot glue gun and a good blade.

1. Trim off any rough edges that might prevent the pieces fitting tightly together.

2. On the underside of the crack use the soldering iron to weld the pieces back together. Tack it at the ends first, then the middle, then work right along the join. I like to work the plastic into reasonably fat little 'bridges' across the crack.

3. Use the soldering iron to make an extra 'keyline' on each side of the join. This will give the hot glue a wider area to bond with the plastic.

4. Smother the weld with plenty of hot glue. If necessary you can tidy the glue up with the soldering iron. (You can also use this method to reinforce any weak spots you think might be prone to cracking in the future)

5. If you stop at this point you'll have a pretty strong repair and the crack on the exposed side will be almost invisible. However I like to seal the joint by running the soldering iron along the front. This ain't pretty but it adds a bit of strength and prevents grit and dust from getting into the crack. If you really want to get serious you can sand the whole joint smooth then paint it. (Rattle cans do a pretty good job).

6. For repairs that require greater strength you can use the soldering iron and glue on the front and back of the join. I did that on the mudguards as they were snapped completely in half, and the repairs were largely hidden under the seat and the steering head.

Normally you will be joining two identical pieces of plastic so they will weld together quite easily. However my front plate presented a further challenge because half of it was completely missing. To patch it up I used a piece of plastic from an old black wastepaper bin. Using a stanley knife I cut a piece to the desired shape then used the soldering iron to weld them together. The weld wasn't perfect because the 2 types of plastic were slighly different but it was good enough to hold together and give a good key for the hot glue. I also used a piece of the bin to make a small holder for the key and neutral light that I fitted behind the front plate. Not pretty but it works and could be painted up one day.

I'm no expert at this. A pro repairer would probably be horrified but it works for me. You can buy specialised plastic 'welders' and plastic filler rods that will do an even better job than this but if you are repairing something for 'go' not 'show' then this is a good start.

(Actually it looks better in real life than it does in these pics. I shot them to hi-light the repairs.)
 

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Last edited:
   / Do it yourself plastic repairs. #2  
Good tips. A guy I know does these types of repairs as a hobby, he generally uses a heatgun and puttyknife to create a "crosshatch" groove pattern on the back side of the broke pieces. They he puts a strip of fiberglass cloth and some resin on the back side for the strength of the repair, the groove pattern is so it sticks good. He then uses the heatgun and puttyknife on the outer surface to melt in and smooth out the crack. If parts are difficult to line up he uses a fast adhesion superglue as a "tack weld" to hold while he does the resin and glass. Once complete he spends a lot of time buffing the parts smooth and the breaks are only visible under the right lighting. They're generally slightly stiffer and an ounce or two heavier, he also generally doesn't have many re-breaks.
 
   / Do it yourself plastic repairs. #3  
Nice job! I hot welded stock on my Omega .50 thumbhole. It cracked by the front swivel, epoxy did not work, but solder fixed it good :)
 
   / Do it yourself plastic repairs. #4  
Epoxy and fiberglass will usually work; but you do have the prep the surface so it will stick.
I've repaired ABS plastic canoes that way and never had a problem; except for the first time when I tried to glue the patch to a smooth shiny surface.
 
   / Do it yourself plastic repairs. #5  
Thanks for posting this thorough tip with pictures!

Nothing to fix at the moment but it's now tucked away in a corner of my noggin for the future.

Ta Mate.
 
   / Do it yourself plastic repairs.
  • Thread Starter
#6  
Thanks for posting this thorough tip with pictures!

Nothing to fix at the moment but it's now tucked away in a corner of my noggin for the future.

Ta Mate.

Its actually quite addictive once you start doing it. I was disappointed when I ran out of things to repair. The hot glue is my own innovation. I think it really adds significant strength to the repair. Its hardens to a stiffness thats similar to the plastic. Not too brittle but not too floppy either.
 
   / Do it yourself plastic repairs. #7  
There are also special types of plastic filler that can be purchased in strips. Don't know about Down Under but here in the US a company called Harbor Freight sells a very simple kit with a soldering iron (with flat tip) and a variety of plastic filler material for about twenty bucks.

Plastic Welding Kit 80 Watt Iron

50 Piece Plastic Welding Rods
 
   / Do it yourself plastic repairs.
  • Thread Starter
#8  
There are also special types of plastic filler that can be purchased in strips. Don't know about Down Under but here in the US a company called Harbor Freight sells a very simple kit with a soldering iron (with flat tip) and a variety of plastic filler material for about twenty bucks.

Plastic Welding Kit 80 Watt Iron
50 Piece Plastic Welding Rods

I mentioned the kits in my first post. I haven't seen them around but I guess they are available over here. The filler strips would be handy. I might try and make a flat tip for my soldering iron.
 
   / Do it yourself plastic repairs. #9  
   / Do it yourself plastic repairs. #10  
Zip ties make good "filler sticks"

and a piece of old screen (metal) can serve as a good backing support when melted into the plastic. Works well.

Plastic welding doesn't help so much with little pieces that have broken off but it works quite well for larger cracks. I helped a buddy repair his bumper fascia with screen and a bit of extra material we used as filler that had been sliced off an area that was not visible. Way better than paying $$$$ for a new bumper cover or $$$ for a professional repair.

The other point I'd make is that the hot air plastic welders are easier to control than the soldering iron type and can do a very nice job with practice. Plastic Welder & Welding Kit
 

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