DIY plastic filler?

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PostPosted: Mon Jan 18, 2021 11:01 pm
My mirror has deep scratches here that I don't think will sand out.

As a DIYer, I was bummed when I read that you cannot use Bondo over plastic since it won't flex with the plastic. What kind of product do I need to get to smooth/fill plastic?

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PostPosted: Tue Jan 19, 2021 5:53 am
This is what I'd do:

1. Leave the filler in the cupboard.

2. Wipe the scratches with a rag soaked in some lacquer thinner. That will probably get rid of most of what's there. Then give it a hit with the buff.

3. What's left you have to make a decision on. Is it big enough to warrant respraying the whole mirror shell or, if you just very carefully touched up, would that do?

4. If the decision is to respray then just sand out those scratches with P180, finish to P400, prime and paint. Don't prime the whole shell, just the bit you've sanded and don't basecoat the whole thing either. Again just enough to cover what you've primed and blend in to the original. then clear the whole shell.

5. Don't believe everything you hear/see/read on the internet. If you do see something that's interesting then get confirmation from another source.
Chris

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PostPosted: Tue Jan 19, 2021 9:40 am
If they won't sand out, they do make filler that stays flexible for plastic bumpers.

But honestly, on a mirror which is pretty hard, I don't think regular filler
would ever be a problem for small scratches.
I see body shops getting away with regular filler on bumpers all the time.
I wouldn't do that but it just shows how durable and flexible
the filler really is. So far a mirror with scratches, not a problem.
But like said above, sanding them out is always best, and any bare plastic
needs adhesion promoter before paint.
JC.

(It's not custom painting-it's custom sanding)



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PostPosted: Tue Jan 19, 2021 11:12 am
NFT5 wrote:This is what I'd do:

1. Leave the filler in the cupboard.

2. Wipe the scratches with a rag soaked in some lacquer thinner. That will probably get rid of most of what's there. Then give it a hit with the buff.

3. What's left you have to make a decision on. Is it big enough to warrant respraying the whole mirror shell or, if you just very carefully touched up, would that do?

4. If the decision is to respray then just sand out those scratches with P180, finish to P400, prime and paint. Don't prime the whole shell, just the bit you've sanded and don't basecoat the whole thing either. Again just enough to cover what you've primed and blend in to the original. then clear the whole shell.

5. Don't believe everything you hear/see/read on the internet. If you do see something that's interesting then get confirmation from another source.



Thanks for the reply, just a few follow up questions to make sure I know what to do.

- By primer do you refer to adhesion promoter or a flex type of filler primer?
- When blending, the color stage, so I just spray like slightly around it to blend? I've never really blended something before. Just fully painted stuff.
- Regarding the rest of the mirror, I was thinking to wetsand 800 grit so be able to re-shoot clear over as well to make it look better?
Last edited by TheMidnightNarwhal on Tue Jan 19, 2021 11:15 am, edited 1 time in total.



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PostPosted: Tue Jan 19, 2021 11:14 am
JCCLARK wrote:If they won't sand out, they do make filler that stays flexible for plastic bumpers.

But honestly, on a mirror which is pretty hard, I don't think regular filler
would ever be a problem for small scratches.
I see body shops getting away with regular filler on bumpers all the time.
I wouldn't do that but it just shows how durable and flexible
the filler really is. So far a mirror with scratches, not a problem.
But like said above, sanding them out is always best, and any bare plastic
needs adhesion promoter before paint.


I was reading that to, on hard non flexible plastic it seems Bondo can pass but still. Idk.

I was also thinking of using JB Weld plastic tan epoxy. Apparently you can sand that and I assume my primer would stick to it.

Thanks I'll so where I go with this. I did try to polish/compound it before with dual action but the damage that was still there seemed pretty bad.

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PostPosted: Tue Jan 19, 2021 7:13 pm
JCCLARK wrote:I see body shops getting away with regular filler on bumpers all the time.
I wouldn't do that but it just shows how durable and flexible
the filler really is. So far a mirror with scratches, not a problem.
But like said above, sanding them out is always best, and any bare plastic
needs adhesion promoter before paint.


The only time I use flexible filler is on those soft rubber skirts that used to be on the underneath of bars. Otherwise it's standard filler all the time. Never had a problem, but I do use quality fillers (3M usually).

I use adhesion promoter when there's a surface that's smooth (e.g. on a new bar) or where there's a textured surface (e.g. also on a new bar) and I don't want to ruin the finish by sanding. Clean, scuff and then AP. Need to be careful though - the solvents in AP are very strong and will ruin the primer if the bar was factory primed.

For repair work I usually finish to P240 on a DA, clean and then use a good 2K primer. AP not necessary when the sanding is this coarse. I've used 1K primer in the same situation, also with very good results.
Chris



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PostPosted: Tue Jan 19, 2021 11:45 pm
NFT5 wrote:
JCCLARK wrote:I see body shops getting away with regular filler on bumpers all the time.
I wouldn't do that but it just shows how durable and flexible
the filler really is. So far a mirror with scratches, not a problem.
But like said above, sanding them out is always best, and any bare plastic
needs adhesion promoter before paint.


The only time I use flexible filler is on those soft rubber skirts that used to be on the underneath of bars. Otherwise it's standard filler all the time. Never had a problem, but I do use quality fillers (3M usually).

I use adhesion promoter when there's a surface that's smooth (e.g. on a new bar) or where there's a textured surface (e.g. also on a new bar) and I don't want to ruin the finish by sanding. Clean, scuff and then AP. Need to be careful though - the solvents in AP are very strong and will ruin the primer if the bar was factory primed.

For repair work I usually finish to P240 on a DA, clean and then use a good 2K primer. AP not necessary when the sanding is this coarse. I've used 1K primer in the same situation, also with very good results.


Hmm okay. I also find that you can buy a spraycan of flex primer that goes on plastic, so maybe I'll just use that, that way it fills the scratch. I assume no AP would be needed if it's a primer made for plastic?

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