Nagging question on filler

[wisconsinjimmy]

:confused: I put the filler on the panel and let it harden, now once it is hardened can I apply more filler over this without sanding or do I have to sand the first coat???

[Hannibal]

If your trying to build up putty, good idea by doing it in layers. Yes I would scuff/featheredge out with 80-120over the putty, maybe going to 220 around the edges.

I would then recommed you use a "flowable" putty as your last step. It does just that: it flows out. It doesnt get pinholes, and will be able to feather better at the edges so you dont see a "seam" where the metal meets the putty. It sands down thinner in my opinion.

So to answer you, yes. You dont want to be at the grocery store parking lot and close your door only to have a 3 pound chunk of bondo fall to the ground By sanding, you assure best adhesion between layers giving a mechanical bond or "tooth".

[Phil V]

Jimmy, just knock off the very outer layer of the existing bondo with a grinder (no need to be picky when grinding, just level it out as best you can with the grinder ) then you can apply more over it

[Dennis N. Schmidt]

You should sand but the reason is not as you might expect. I has to do with the chemistry of polyester. Almost all polyesters are parafinated with spray surfacers (such as G2) being an exception. What this means is that paraffin (wax) is added to them to act as a protective layer. In use the paraffin floats to the top of the covered area and then is removed by either a solvent or sanding. To save on sandpaper you should always wipe Bondo with thinner prior to sanding as it will completely prevent the loading of your sandpaper if you do this.

Wipe a rag damp with thinner over your Bondoed area. It will remove the shine from the Bondo (this is the wax) and you will see a residue on your rag which is the removed paraffin.
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[Mooch]

Well I'll be dammed. Dennis I have been doing that for too many years to remember .I know it works but didn't know it was wax.

Ricco

[wisconsinjimmy]

Gentlemen I thank you for your advise that takes a big load of the mind and puts me at ease and wipe thinner over the fresh filler I will do that wow saves a bunch of work, like I used to put enough dust on the floor to build a vette darn rookie I am.
Thank you

[MARTINSR]

The first question I have is why would you ever need to apply filler over filler that wasn't being sanded??

The first coat of filler is for roughing your work into shape. It SHOULD need sanding to do that. If you are filling such a low spot that one coat of filler isn't enough to even need sanding, me thinks you need to do more metal work.

I know, I did that once many years ago on a top chop. I poured two gallons of filler on that roof before touching it with sand paper!!!

Should have made the metal nicer before starting the filler work.

Brian

[68-chevyman]

Brian, That metal work is just part of the job arn't it. As to the thinner cleaning something sounds wrong about that:confused:

[MARTINSR]

I didn't even touch on that, don't like it a bit. Just sand it and you don't have to introduce something like thinner to "possibly cause a problem. If all else fails, give the manufacturer of the product a call. I have called the Evercoat tech line a number of times and they are always quick and helpful.

Brian