Bondo vs Fiberglass for fillers?

[Superman74]

The rear apron of my super has been built up using regular pink bond.. it has failed in spots and in looking around the parts store i see fiberglass bondo, conventional bondo, "gold" bondo…. but little info on the proper uses and differences of each.. thoughts???

[modok]

For one thing most are porous like, well, lets say whipped cream.
So they must be coated with a sealer, but are lighter and maybe more flexible than if it wasn't whipped.

Then there is non-porous spot putty, which works just like regular except isn't porous. it's a bit heavier, can be useful as a second coat over the regular filler or for small touch ups. If you try the fiberglass stuff then this would be good to put over it and get a good finish.

IMO if any filler it is applied too thick or used in areas that flex or get too hot then it will crack.

The fiber-glass stuff is horrible to work with but it is stronger, and heavy. Does seem to add some strength but really I haven't found much use for it. Probably good to use to repair fiberglass with.

[skills@eurocarsplus]

replace the apron. they get hot on stock applications and you will have to deal with sinkage/repeat failures in that area. just my .02
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[Matt K.]

Sometimes the failure is a cheap product and sometimes the failure is due to the fact of a inexperienced repair.....I have always had really good luck with the "Gold" fillers....products such as Evercoat make great fillers. If I have welded a part together I use a skim coat of a fiberglass based filler such as "Durglas" over the top of the welded areas because the fiberglass based filler are moisture proof and regular fillers are not that way if there is a tiny pin hole in the welded area where moisture could get through the fiberglass product will not absorb it as a regular filler would.
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[Derek Cobb]

The heating and cooling from the exhaust will just cook the filler on the apron. Replace it if it needs anything more than a skim coat.

[Dr OnHolliday]

I always "heard" that bondo shouldn't be more than 1/8" thick....and I think that's pushing it...
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[punkabillyvw]

max thickness for bondo is 1/4" after that any flex at all will crack, have large amount of pinholes fiberglass is horrid to work with but quite strong all metal is a bondo style product with metal shaving in it stronger than fiberglass but also quite pricey for the amount the route i would personally run is to get a soldering gun and fill it with either solder or lead {lead can be got extremely cheap most tire shops will donate there old wheel weights} this gets rid of the flex issue porosity issue and heat problems and when done properly cant even tell it was ever repaired

[Chickensoup]

I know this may be a long shot but I found the last bit of rot on my 65. Under the rear windshield. My dad used fiberglass filler to cover similar rot entirely.

Would fiberglass filler hold up on something like this?

Thanks

If not, I have access to a donar car. But as you know double layer complex shapes can be time consuming.
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'65 Tourist Delivery Build
'66 RIP
'69 RIP
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[Braukuche]

If you never get it wet you POR15 it and you remove the active rust it will last a while but it’s no replacement for doing it right. But sometimes it doesn’t make sense to do it right.
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[Breadford]

Cut that rust out, and weld new piece of metal. If you use fiberglass, it will be worse over time.

[Chickensoup]

yeah i figured the filler would be a bad idea. plus the idea with the car was to get the body so straight filler would only be needed as skim coat.

i will just make my own bends first and see if they turn out well.

thanks
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-'85 c10 5.3 LS, 222 cam, long tubes, x pipe, 3 inch spin tech's
-'05 B5.5 TDI Wagon 17in sport rims ;EGR + BSM + ASV Delete, Stage-2 Tune, straight pipe
'65 Tourist Delivery Build
'66 RIP
'69 RIP
Hosea 4:6 "My people are destroyed for lack of knowledge"

[Dan the workingstiff]

I would also be tempted to try my own patch pieces first.
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