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Old 10-05-2008, 02:58 PM   #1
Greg in H-Town
 
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Best material for filling deep scratches in plastic?

So a couple of weeks ago I joined "Wrecked my bike" club. I was on a commute and hit a patch of wet pine needles, and it was all 'meet the street' after that. The gear did its job, so just some aches and pains - nothing serious.

The main thing is that the bike appears to be fine - rashed up fairings, bent front brake lever (fixed), bar end, turn signal, muffler flange all scraped up a little. The lower right fairing and some other bits are on order, but there are some scrapes on the upper fairing that I plan to fix myself. Some scratches are pretty deep and I don't think they'll sand out easily - what's the best filler for that?
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Old 10-05-2008, 03:54 PM   #2
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Re: Best material for filling deep scratches in plastic?

I've never used this product but this is what I found doing research after my bike had a run-in with a pad lock. G.T. Motorsports
Plastex Repair Kit
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Old 10-05-2008, 04:02 PM   #3
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Re: Best material for filling deep scratches in plastic?

If you plan to repaint the area, I've had good results with JB Weld. Mix up a batch, push it into the gouges (try not to leave too much around it but fill it at least to the level of the surface), then let it sit AT LEAST 24 HOURS and then wet sand it smooth with a medium then fine sanding block.
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Old 10-05-2008, 05:57 PM   #4
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Re: Best material for filling deep scratches in plastic?

Epoxy mixed with enough wood flour to make a smooth peanut butter-like consistency, work it into the crack, cover it with Saran wrap, then roll it smooth with a rolling pin. Very little sanding after rolling it out.
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Old 10-05-2008, 06:05 PM   #5
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Re: Best material for filling deep scratches in plastic?

I have used 3m automix #5895 a/b parts, ez sand flexible parts repair kit on car bumpers. Like Squeaky said, I think the JB weld would work on a fairing. Good luck with it. RH
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Old 10-05-2008, 06:45 PM   #6
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Re: Best material for filling deep scratches in plastic?

I'm a little confused about the JB Weld suggestion; the stuff I'm thinking of is for metal repairs - is there a different version, or is it more useful than I thought?
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Old 10-05-2008, 07:37 PM   #7
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Re: Best material for filling deep scratches in plastic?

It's used for all kinds of repairs. Not JB Quick, just regular 'ol JB Weld. Two tubes, mix up a small amount, and use it like a spackle. Even on plastics that need some flexibility I've never had it crack or flake.
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Old 10-05-2008, 07:53 PM   #8
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Re: Best material for filling deep scratches in plastic?

Cool - I was hoping you meant the regular stuff because I have some in the toolbox. The OEM replacement for the lower fairing and the Zero Gravity dark smoke windshield will be here this week - it just kills me to see the Zed banged up. Just paid the dang thing off too.
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Old 10-05-2008, 09:40 PM   #9
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Re: Best material for filling deep scratches in plastic?

JB Weld is just a REALLY good epoxy, that's why they compare themselves to steel and welding. I called them years ago and they told me it was good to 1200+ degrees, after that it turned to dust! RH
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Old 10-06-2008, 11:26 AM   #10
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Re: Best material for filling deep scratches in plastic?

evercoat makes polyester filling. sands easier than bondo and works well. as long as u sand area prior to applying it so it bonds well. shoot little primer and paint. most auto paint stores prolly carry it or something similar. plus u can get it in quart i think for not much $$$. as long as its scratch and not crack it will work nicely.
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Old 10-06-2008, 12:47 PM   #11
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Re: Best material for filling deep scratches in plastic?

I will have to try the JB weld as well to fix the corner scratches in my front fairing.. now if I can just get the proper red color for my tiger
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Old 10-06-2008, 12:53 PM   #12
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Re: Best material for filling deep scratches in plastic?

I've used the evercoat polyester. That's good stuff, sands nicely. But, somewhat pricey and it doesn't have a lot of build, so it depends on how big the scratches are. If they are deeper than 1/8th to a 1/16th, he might need multiple coats. A regular body filler (with no fiberglass in it) would work better on something deep. It'd be cheaper than the polyester too. I don't have any specific brand recommendations.
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Old 10-06-2008, 02:28 PM   #13
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Re: Best material for filling deep scratches in plastic?

depends on how u plan on finishing it? JB wont finish for crap..and u cant paint it and it look good. so u need something thats sandable, will hold paint and primer. go to autobody paint store, yes u can get stuff at autozone and such, but if u want it nice, get to good paint store and see what they have.
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Old 10-06-2008, 11:41 PM   #14
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Re: Best material for filling deep scratches in plastic?

Epoxy products do not sand well because the heat from power sanding softens the material. JB Weld may be an exception. That is why I posted the Saran wrap roller idea. Saran wrap and a metal roller can save days of hand sanding when building a fiberglass/epoxy/plywood composite boat.

Polyester does not bond well to anything except itself, and even then only when it is laid wet-on-wet. Polyester absorbs humidity that causes it to swell, then gives up the humidity when exposed to dry weather, which causes it to shrink and crack. Polyester is more easily cracked by vibration and distortion than epoxy. Most auto body fillers, including Bondo, are polyester.

I suggest this kit for small jobs as it is complete with everything you need to repair scratches and cracks except Saran wrap and a roller (a roll of quarters makes a very good roller):

http://www.bateau.com/proddetail.php?prod=E_try
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Old 10-07-2008, 08:19 AM   #15
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Re: Best material for filling deep scratches in plastic?

Quote:
Originally Posted by KenH View Post
Polyester does not bond well to anything except itself, and even then only when it is laid wet-on-wet. Polyester absorbs humidity that causes it to swell, then gives up the humidity when exposed to dry weather, which causes it to shrink and crack. Polyester is more easily cracked by vibration and distortion than epoxy. Most auto body fillers, including Bondo, are polyester.
Polyester bonds fine to metal, fiberglass, and the couple of scuffs that were repaired on my plastics. Just scuff up the area properly and make sure it's clean. I don't have a ton of experience with the stuff, but its been used for what, 40 years in autobody shops, and the manufacturers have been improving it since it first came out. Originally it had a lot more problems than it does today.

It does breathe humidity, like you say...which is why you paint it. Problem solved.

I don't think there is anything wrong going this route at all...I think I will try the saran wrap and rolling pin idea though on my car..I'm glassing in some pop up headlights and that may just be the ticket.
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Old 10-07-2008, 09:49 AM   #16
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Re: Best material for filling deep scratches in plastic?

Hand sanding the epoxy works fine. just be aware that it is harder than the plastic around it, so use a block to prevent sanding a moat around the repair.

+1 on using wood flour to make a paste using two part epoxy. It improves the sanding quality tremendously and is an old boat building technique. For repairs as small and shallow as you are doing the JB Weld right out of the tubes should be fine. As Squeaky said, apply it as smooth as possible to minimize sanding later. One thing I would add is to resist over working it as this can introduce voids and reduce adhesion.
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Old 10-07-2008, 10:36 AM   #17
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Re: Best material for filling deep scratches in plastic?

Quote:
Originally Posted by Diderich View Post
Polyester bonds fine to metal, fiberglass, ...
The entire DIY composite boat-building and aircraft-building industries disagree with you.

Quote:
Originally Posted by Diderich View Post
... I don't have a ton of experience with the stuff, ...
I've only built a few hundred boats (worked for Donzi/Thunderbird), sailboat spars, 1 airplane, a couple dozen car, dune buggy, truck, and swamp buggy bodies, countless replacement body panels, even a few motorcycle fairings, seat bases, fenders, and side covers with both epoxy and polyester. I've used methods ranging from chopper gun 'glass and polyester in a female mold to hand-laid and vacuum-bagged Kevlar and epoxy on a plug to self-jigging fiberglass/epoxy/plywood composite.

I designed and built a tunnel hull for personal use. No structural problems at 120mph. Two brothers bought the plans and substituted polyester resin for the specified epoxy resin. They built two boats and both delaminated on their maiden voyages, killing both brothers. It is no fun facing a multi-million dollar liability suit. I won because the building manual explicitly warned against using polyester resin, the BOM specified a specific brand and formulation of epoxy, the surviving family members could not produce a receipt for any type resin except polyester, and I salvaged the wrecks for the engines, along with saving some of the wreckage as visual displays of what happens when people don't follow instructions.

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... its been used for what, 40 years in autobody shops, and the manufacturers have been improving it since it first came out. ...
Bondo has been cracking and popping off repairs for 40 years. It is better than it used to be, but it is still not as good as epoxy. The $25 trial kit has enough materials for several repairs. It only costs a few dollars to upgrade materials. It would be penny-wise and pound-foolish not to do so.
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Old 10-07-2008, 04:21 PM   #18
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Re: Best material for filling deep scratches in plastic?

Well, the majority of the auto industry disagrees with you, Ken.

That said, some guys won't use anything other than lead solder.

But here we're talking about cosmetic surgery on low quality plastic. Its ABS or some crap like that, not carbon fiber epoxy or hand hammered aluminum jag panels.

We're also not talking about about a cheap body shop slopping on a half inch thick coat of the stuff to save the time of pulling the dent first. This is exactly what body fillers are designed for, filling in little dips and scratches for a smooth finish coat. From the description of the damage, i didn't get the impression that this was a structural repair or I'd agree with you whole heartedly. If the plastic is cracked for example, the filler won't last a week...If he's just filing in some superficial gouges, filler is a lot easier and cheaper. It sands nice and smooth for a good looking paint finish. And a quart is about 6 bucks...obtainable at most automotive stores....

I'm sure the epoxy is great, but unless I misunderstood the repair, its overkill. I wouldn't make any boat hulls out of bondo but, to fill in some scratches that he was talking about possibly sanding out anyways? I'd use the body filler.

I'm just some idiot on the internet though.
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Old 10-07-2008, 04:27 PM   #19
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Re: Best material for filling deep scratches in plastic?

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Originally Posted by LongR1 View Post
depends on how u plan on finishing it? JB wont finish for crap..and u cant paint it and it look good. so u need something thats sandable, will hold paint and primer.
I've used it for dings and scratches on helmets, fairings, and saddle bag covers. Never had an issue with paint adhesion or finishing.
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Old 10-07-2008, 04:47 PM   #20
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Re: Best material for filling deep scratches in plastic?

thats cool.. never used it like that...but my dad was body shop manager for 40 years, so i always had access to good stuff. would guess its alot harder to sand than bondo or some sort.
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