Old Bondo

[MisterCinders]

Repainted my tank recently and it looks pretty crappy.

My main problem is some old bondo. After I stripped the old paint, I discovered that a PO had repaired a couple dings and sizable dent with body filler. I did not redo the bondo job, and my sanding/smoothing were insufficient to level and blend the filler surface.

I will probably re-strip the tank and try again. Should I dig out the old bondo and replace it with new material? The filler itself is not cracked or crumbling, it just is not even with the surface.

Oddly enough, the old paint did not show any bondo, so I managed to botch a smooth filler patch when I re-did the work.

TIA

[Paul's Zuki]

yeah, sand it out and throw some fresh stuff on there. It's better to know what your working with than building on what the PO did. It wouldn't take you much longer to get that stuff out anyways.

[Hammered]

If the old bondo is holding and not flaking off, leave it. Just sand the tank smooth and you can leave the old/new paint as primer. No need to go to bare metal. All that will do is expose the metal to all sorts of nastys like finger oils, humidity and worse. If you dont already have a sanding block, get one. Something that flexes front to back. That will help on the rounded surfaces. Most of the Harry Homeowher stores here have them.

[Nessism]

Another vote to remove the old filler. It's not much extra work and it's always good to make sure the job was done right in terms of pulling the dent as much as possible and roughing up the metal for good adhesion.

And speaking of filler, the cheap "Bondo" brand stuff has a medium-bad reputation for shrinkage and show though but their Prestige version is good. Bondo is now made by 3M (I don't think that was always the case) and they don't make junk.

[Dave8338]

Yep, as mentioned, leave the old stuff in. It has shrunk to as "tight" as it is going to get. Also as mentioned, leave you paint/primer on and start with some 400 grit wet/dry (use it wet) and a rubber sanding block. You will quickly discover, how the paint you applied, acts as a filler for smoothing out the bondo lines. DO NOT use just a piece of sand paper and your hand until the last coat of primer or you will have waves that will show through the paint.

[ddaniels]

I agree to leave the old bondo in. What's the point of removing it if it's been there a while and is solidly bonded to the metal?

[MisterCinders]

Remove it . . . leave it . . . remove it . . . leave it.

It's Chinatown, Jake!!

[AF_Bill]

IMO, I'd leave it unless i was gonna try and fix the tank. BUT, you might be better off leaving it.

[81GS750]

I'd suggest remove it all down to bare metal and do the job properly.

[cal_look_zero]

My question is how "show worthy" are you going?

If it's a 3 foot job, then just leave the old stuff, go to an auto paint supply and get some "icing" or go here...

http://compare.ebay.com/like/220761052364?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y

It's about the consistency of cold maple syrup and will be able to fill in smaller dings, plus it's incredibly easy to work with. Sands easily too. I vote STRONGLY against wet sanding any filler materials until you have a primer coat on them. Uncoated fillers are sponges for contaminants and will ruin your day when you get primer wrinkle from oils or moisture getting trapped.

[beergood]

I wouldn't remove the old stuff unless you have to. That being said, if you have access to an angle grinder, buy a $14 twisted metal brush for it. It chews through old bondo like hot butter.

Now here is the real tip: Glazing Putty.

Bondo body filler works great for filling in larger areas. It is also very difficult to feather into metal seamlessly. That is where this stuff fits in. It's cheap ($6 a tube, which goes a long way), easy to use, and gives great results.

http://www.ehow.com/how_2112839_glazing-compound-auto-body-work.html

It is a real time saver, and once you use it you will be mad you hadn't tried it before.

Also, use sandable primer, or filler primer. It leaves a slightly heavier coat.

[81GS750]

If you want to go all out Spies Hecker makes a sprayable high build polyester. I've used this product on multiple jobs and it works excellent. You don't want to spray this stuff over bare metal, just rough up the existing work with some 80 grit and spray this stuff through your primer gun.

[MisterCinders]

Wow - information overload. But in a good way

On further reflection, I will stick with my ghetto paintjob for a bit (so I can ride the damn thing).

Given the position of the biggest filler patch, I am leaning toward stripping the paint and the filler (at least the big spot) and taking a crack at hammering in some knee dents.

I already have a cafe seat and tail light set-up, so might as well go all in.

On that front, I know from other threads the basics of marking off and banging in the sides, followed by some filler to smooth out the surface. What do you guys think of this possible "cheat"?

I see cafe tanks that have what looks like a rubber pad in the indents. Based on that, it might use a similar approach to mask the surface once the indents are shaped. Essentially, I start with the following SOP:

• strip tank
• mark off indent areas
• use the gentle banging method to rough out (in?) the indents
• use some filler to smooth the new indent surfaces
• sand that down as much as I can

Now my clumsy ape-like skills are not likely to yield a smooth indent surface. So at this point, I wonder if a different surface cover might work better. I was thinking of using a spray-in liner material or some kind of textured rubber sheet on the indents.

Any thoughts on this approach?

[beergood]

I've tried (and failed) to find some sort of rubber insert for my tank that doesn't look terrible. So, if you come up with something, let me know.

I am sure I could fab up something, but I don't think anything I could make would be less work than just smoothing it over with filler and painting it.

Let me give you another tip: if you are going to hammer your tank, find some sort of spacer to put in the tunnel. My tunnel closed a little. You can't tell from looking at it, and I bet the actual deformation is really slight, but it makes it really tight around the mounting pucks. It was sort of a drag. Not a life and death sort of a deal, but one I would avoid had I been warned.

You could also try hammering it on the frame, but I think it is more helpful to be able to move the tank around.

[nvr2old]

Not trying to discourage you at all, but if you're leery of re-doing an existing dent already, pounding in knee dents should be the last thing you should attempt. It's so much more involved then just taking a hammer to it and then smoothing it out. It's major body work. Just saying....