Patching Plastic

[DirtyDamage]

I need to patch a fairly large hole in the side of my go karts bodywork(See pic, on the numbers) , as well as some cracks and other breaks. I don't know what to use to patch the plastic or how to do it either...(if only it was metal) I need it to be black...

It was suggested to use fiberglass mat and plastic epoxy, but not to sure how to approach that.

Thanks for the input

 

[KartFab]

I have no experience and little knowledge in this, but I remember seeing plastic welders at harbor freight (not welders made of plastic, which I am sure there is a high percentage of plastic in welders you get at harbor freight). I know that there are different types of plastic though so some investigating is going to be in order.

 

[DirtyDamage]

I think it's HDPE but I'll have to check next time i'm in the shop.

 

[JMINDY]

I haven't done fiberglass work, just metal fab and bodywork... but this is how I would take a stab at it... I would find a piece of plastic sheet that is the same thickness as your side pod. With a piece of tag board behind the hole, I'd trace out a pattern and cut it out of the new plastic sheet to plug the hole. Then glue in the plug by layering multiple strips of fiberglass mat and resin on the back side. Then fill in the seam/remaining gaps on the front side with a plastic epoxy. Sand it level.

If you wanted a seamless painted finish, then I'd do a light skim coat of body filler, sand, filler primer, sand again, prime and paint.

But if you a racing, I would probably sand down the plastic epoxy as level/smooth as possible, paint black and then cover any remaining visible seam with a new number sticker.

 

[XHASHNUTSX]

doesent seem like to bad of a hole, put a fiberglass patch on inside and one on the outside after it drys up sand it down and feather it out on the outside clean then repaint. don't be afraid of fiberglassing I did it in A&P school its a lot easier than you think it is just get the smallest amount of resin it will come with both parts mix it according to directions, get the fiberglass matt not chopped matt from lowes. you will spend about 35 dollars and have plenty left over for future patches

 

[crazykart]

That's the thing, fiberglass resin doesn't like to stick to plastic...it will come off. The mat can be used as filler though with a plastic epoxy, and is very strong.

Grind around 3-4" the back side of the hole, rough it up good. Lightly rough up around the front side of the hole about 1" out (120 grit sandpaper works well). Take a piece of wax paper and lay it over the hole, then use cardboard over that taped down firm. Flip the kart body back over to the inside and lay some plastic epoxy in it so that the outside is filled and smooth. Lay a piece of fiberglass cloth or mat in the hole, cut it about 1" bigger then the hoke and make sure to push it in good all around. Lay some more epoxy on the cloth of mat, then another piece of cloth of mat about 2-3" bigger then the hole. Again fill with plastic epoxy (you can get the 2 part plastic epoxy at harbor freight for cheap) cover the mat/cloth and extend the epoxy out to the edge of where you roughed it up. Let it dry overnight, then take off the cardboard and wax paper. You may have to do some light sanding to make it seamless, and may possibly have to lightly rough up the outside and lay a thin coat of epoxy.

If done right you should have a seamless very strong repair.

The best part is that you can mix a few drops of whatever color paint the kart body is into the epoxy while you mix the 2 parts to match the body perfectly, or near perfect.

I've done this on broken ground effects and it's worked perfectly, and held up for years with no signs of cracking/chipping/anything.

 

[XHASHNUTSX]

That's the thing, fiberglass resin doesn't like to stick to plastic...it will come off. The mat can be used as filler though with a plastic epoxy, and is very strong.

Grind around 3-4" the back side of the hole, rough it up good. Lightly rough up around the front side of the hole about 1" out (120 grit sandpaper works well). Take a piece of wax paper and lay it over the hole, then use cardboard over that taped down firm. Flip the kart body back over to the inside and lay some plastic epoxy in it so that the outside is filled and smooth. Lay a piece of fiberglass cloth or mat in the hole, cut it about 1" bigger then the hoke and make sure to push it in good all around. Lay some more epoxy on the cloth of mat, then another piece of cloth of mat about 2-3" bigger then the hole. Again fill with plastic epoxy (you can get the 2 part plastic epoxy at harbor freight for cheap) cover the mat/cloth and extend the epoxy out to the edge of where you roughed it up. Let it dry overnight, then take off the cardboard and wax paper. You may have to do some light sanding to make it seamless, and may possibly have to lightly rough up the outside and lay a thin coat of epoxy.

If done right you should have a seamless very strong repair.

The best part is that you can mix a few drops of whatever color paint the kart body is into the epoxy while you mix the 2 parts to match the body perfectly, or near perfect.

I've done this on broken ground effects and it's worked perfectly, and held up for years with no signs of cracking/chipping/anything.

you are way better at explaining things

 

[itsid]

So.. where do I start?

....then from his rib he formed... a little too early...

Now first of all, you must know what plastic that bumper is made of!
that is VERY important.. different types of plastic MAY or MAY NOT bond well.

we can be sure it's thermoplastic, but which one?

got it?

Perfect! get a similarly colored piece of plastic of the same type (ABS, PE, PP, PU... whatever the side pod is made of)
(easiest way.. find a totally useless single side pod same make and model and salvage it for patches)

Now cut a patch that fits (minor gaps are not important)
[see I was too late actually.. from this rib he formed ]


Now that you got this far.. go to the next hardwarestore and buy 'plastic welding sticks'
it's exactly what you think it is.. small rods of thermoplastic (carefull it too comes in different flavours, use the matching one!)
most are available in (off-)white, black, tan and grey; I'd suggest a black one for obvious reasons.

If they don't have it, go to the next bigger store and try again.
worst case: amazon

Now that you have it you can get a welding gun for it as well...
or you save the money and use a simple low power (no more than ~80Watts) soldering iron with a flat tip (screwdriver thingy)
tape the back of the patch with duck tape to hold it in place...
and work your way around with the soldering iron adding small amounts of the plastic welding stick.

you're done!

to beautify the result, you can use some fine grit sandpaper and a flatiron to add minor texture. (don't move, just press lightly and wait)

'sid

 

[DirtyDamage]

I think I'm going to try the fiberglass. Seems cheap enough to do and from what I've seen searching YouTube easier than I thought.

 

[DirtyDamage]

Also probably going to start a build thread on it. Seems like something always needs fixed or rebuilt. But the good part is these karts are made for that. Everything is made to be fixed repaired or changed on the fly. Just ordered some new parts too. ��

 

[itsid]

easier than ...

say this:
http://www.youtube.com/watch?v=61iyLarL258



'sid

 

[DirtyDamage]

My only concern is finding filler plastic. Like you said above then doing what he's doing

 

[itsid]

That's not actually a problem.
You'll find a stamp telling you what plastic it is,
like you find on plastic bottles, plastic bags and any plastic part around your house.
(recycle centers NEED those stamps to sort)
you can use that same stamp to repair.

As you can see in the video he's salvaging a spray bottle as a filler material.

Personally.. I doubt it's an ABS bottle (he said so though) most bottles are PE, at least around here.

And PE and ABS do not bond too well,
the perfect bond is achieved using the same material (minor mix differences are not important)
and in the end, technically the part itself is 'as new' maybe not cosmetically,
but done right, the inner material bond of the repair is identical to the inner material bond of the uncracked part.

While fiberglass is a great material (also for repairs) it can't do that.


Don't get me wrong, whatever you feel confident and comfortable might be the choice to pick (as long as it's not utterly stupid of course)
but really.. plastic welding is as easy as using a glue gun to write a letter

clean the parts (alcohol works fine) apply heat and where necessary filling material, maybe cut off excess... done, rest is cosmetics.

'sid

PS search yt for more videos if you want, some use heat guns, some special welders...
some a propane powered pocked soldering iron...
as long as it's hot it'll work