Filling Warped Fender Flares (With pics)

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PostPosted: Sun Aug 05, 2018 5:39 am
Morning all,

I have a 1979 Mercedes Benz G Wagon.

I have just repainted the whole truck after some rust repair and as part of the job I ordered some new fender flares from a small garage in my home country. ( I now live oversees so my brother picked them up and brought them to me when he came to visit)

I'm not sure what happened to them, either the flares used to make the mold were old and warped or they were pulled too quickly... but they need work. The original ones had split and cracked beyond repair.

Problem 1
They do not sit plum on the body, if you bolt the lower front end on the back pulls away from the body and visa versa. When you put all the bolts in they line up quite nicely and they fit, but there is a bit of "rotational" twist in them.

Problem 2
They are not flat across the top or along the sides. If you look at the below image of the original fenders they are smooth across the top. Mine have some eighth inch dips and waves in them.

0390070820_800_600x600.jpg


So I need to work out what to do to fix them and would like your comments.

- I can live with the twist in them as long as it is not going to crack the primer and paint when I paint them (Epoxy Primer + Single Stage Urethane Black Bumper Paint)

- I need to fix the waves and I plan to do that with Upol Glass Reinforced Filler (its all I have been able to find, I used it to plug about 20 holes in the roof and it shrunk a fair bit but once cured it was hard as hell and a real job to sand even with 60).

u-pol-david-s-isopon-p40-glass-fibre-repair-bridges-holes-rust-2-sizes-available-[2]-3299-p.jpg
u-pol-david-s-isopon-p40-glass-fibre-repair-bridges-holes-rust-2-sizes-available-[2]-3299-p.jpg (18.85 KiB) Viewed 5243 times


- I have a concern that if I put a thick skim coat of the filler (possibly 1/8th inch in places) on the fenders and then sand it down and paint it.... When I then bolt them up to the car the filler is stressed from the twist and could separate/crack.

- I can do the filler work with them bolted up to the car but I then want to take them off to paint them and am concerned that taking them off will then flex them as the filler will be fighting the flex created when they were molded.

- When I was a kid and I did some glass work with my dad on boats we would drill small right through thinner glass panels to allow any new layers to anchor to the older ones, is that something I need to consider doing to fix the waves on these, or will sanding down to 80 be sufficient to create a mechanical bond.

.... So whats the best way forward?

1. Fit to vehicle and let them stand in the heat for a few weeks (its 115 degrees F, on average here at the moment - Qatar, The Middle East)

2. Drill some small holes in them to let the filler bite through the fender.

3. Apply filler to smooth out the waves on the top and sides. Give it loads of time to setup and shrink.

4. Remove (hope to hell the filler holds) paint and reinstall.
Last edited by RSF Gunney on Mon Aug 06, 2018 12:48 pm, edited 1 time in total.

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PostPosted: Sun Aug 05, 2018 9:26 pm
I assume these flares are made of some sort of plastic, rather than fiberglass?
If so, I'd carefully apply heat with a propane torch and try to twist them back into shape to fit the fenders better. A large oven would work too. Try to get the torsional stress out of the flares before using any fillers.

There are also fillers specific for plastic bumpers that would be better than the filler you have, but availability might be a problem...
"If you can't move it, paint it." - U.S. Army



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PostPosted: Mon Aug 06, 2018 1:18 am
Thanks for the reply,

They are made of fiberglass.

The original ones were made of some kind of rubber, however my replacement ones are fiberglass so the repair job will be fiberglass + fiberglass filler + primer and top coat with flex agent.

Thanks,
J

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PostPosted: Mon Aug 06, 2018 8:40 am
You can work out problems like this in fiberglass by usually "jigging" the parts to just beyond where you want them to "stay" and leaving them in that hot sun of yours for few days. The problem is going to be trying to get them to "stay" that way when exposed to that sun on a regular basis (yes, even with putting more lay up or reinforcement underneath). With a 115 degree day and the fact they will be black you will be heading to a 165 to 200 F degree surface temp. Most normal aftermarket parts start moving in as little as 150 degrees and can be completely distorted by 200 F. Another huge problem I see here is temperature cycling. Heat/expand, Cool/shrink, repeat.....and on, and on. This will lead to micro cracking in the fiberglass and surely start separating any normal fillers from it.

Your best shot (if you just have to stay with these things) would be to manipulate (jig) stuff to where you want it and add more compatible resin/mat/cloth from underneath to increase thickness in an attempt to get these shapes to hold out in that sun. If it was me here facing that problem I would be considering adding 1 inch of polyfoam underneath and glassing that in. The foam would act as a stiffener and also serve as thermal barrier so the heat on the outside could not transfer as much to the cooler inside stiffening material.

And my best solution? I'd find a local panel beater and get those things made in steel, aluminum, or just about anything more temp. stable than fiberglass.
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PostPosted: Mon Aug 06, 2018 12:45 pm
Thanks for the feedback. Yes the heat here is a big issue.

Here are some pictures of the fenders. As bad as the pictires are they should show the warp and wobble and dips in the tops of the flares.

Top of the fender with the "dip"

20180806_203114.jpg


Easier to see here where my thumb is.

Screenshot_20180806-203850_Gallery.jpg


Another one.

20180806_203944.jpg


There's one straight one.

20180806_203934.jpg


The sides need to be tidied up.

Screenshot_20180806-204312_Gallery.jpg



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PostPosted: Mon Aug 06, 2018 12:47 pm
They're very thick and heavy. I suppose I can add to the back of them. I have no experience with fiberglassing but I suppose I can experiment :pcorn:

Screenshot_20180806-204323_Gallery.jpg

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PostPosted: Mon Aug 06, 2018 1:49 pm
I hate to say this but those are fairly good aftermarket fiberglass parts..... You got minor shrinkage and movement because of the way they are configured. Heavy well supported areas with much, much thinner straight sections between is what I see there. Thin areas cure out faster while the heavy areas shrink slower and "pull" the straight areas into distortion.

Again, for no more than you've got going on you could fiberglass some steel bar stock clamped in place. The unknown variable in doing that though is again heat. I'd be afraid of leaving it in place because of heat loading in the steel which could cause it to delaminate.

That looks like such easy stuff if I was doing it for "here" but that heat over there is just incredible.....and it makes any plastic/fiberglass susceptible to movement.....
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PostPosted: Mon Aug 06, 2018 2:28 pm
Thanks for the feedback, makes sence when you put it that way.

I think I might install them and look to make a few stress releasing cuts if I still have major concern.

If I'm going to have to use the equivalent of Dynaglass over most of the surface to get them to look decent then a few cuts should not be too much extra to deal with.

Please correct me if I'm wrong but Dynaglass is essentially the same thing as if I made up my own resin mixture with chopped glass?

(I.e. it will be fine to use to make my "smoothing" skim coat)... The reason I ask is because I can get fairly good autobody products here but the fiberglass works stuff is all no name brand out of Pakistan and Iran and I have no idea what the quality will be like.

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PostPosted: Mon Aug 06, 2018 2:58 pm
Stress relief cuts are an excellent idea.....if you can "spread" the tension you stand a lot better chance of it holding up to the heat.
I had to look up Dynaglass just to make sure.....but yes, it is made of short hairs and milled fiberglass and most importantly they state right in their p. sheets that it can be used with mat and cloth. I think it would be okay for what you are trying to do. It is a true waterproof filler which means it is probably straight polyester with no clay or talc.
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PostPosted: Mon Aug 06, 2018 4:14 pm
Thank you. Really appreciate the feedback and guidance! :D
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