Topic: What body filler to use when smothing knee dents on gas tank?

[m511y]

So I just finished hammering out some knee dents in my tank and it came out very well. Know I have to tackle the task of filling in my emblem indentations and smoothing out the knee dents.

I have done a little bit of searching and I found that some people recommend to just use regular bondo, some say to use kitty hair, some say fiberglass resin. I often see people using greenish bondo when doing auto body work, but I don't know anything about it. Is this plastic body filler? Does anyone know the advantages or disadvantages to these options when dealing with smoothing out my knee dents as well as filling in the badge recess. I would like to give the green stuff a try. Has anyone used it?

Any help is appreciated.

[mystic_1]

Bondo should be applied as thin as possible otherwise you end up with problems later on (it shrinks).

If you need to build up more than say 1/8 inch of thickness, use a reinforced filler like Tiger Hair, then top it off with bondo.

mystic_1

[Industrial Cafe]

jb-weld. expensive, permanent.

[bucky katt]

duraglas with a final VERY thin skin of bondo on top.

[Industrial Cafe]

+1 on that

[m511y]

Ok, duraglas with a slim layer of bondo it is. Any more tips? I have been researching body work/filler for a long time now, but this will be my first attempt. I'm crossing my fingers.

[Industrial Cafe]

sand in an x format

[mystic_1]

Take care with your mixing, both in terms of ratio of hardener, and in the actual technique you use to mix.

Do not stir, this introduces air bubbles.  After you've measured out the hardener into your pile of goo (don't mix too large a batch), take a plastic applicator, and "wipe" across the pile, smearing the hardener into the bondo.  Then scoop up the smeared out pile, fold in in half, and repeat.  It's awkward to describe in words, look for a youtube vid maybe, but the idea is to not introduce air bubbles.

The same technique applies with epoxy resins, btw, you want to take care not to introduce air bubbles.

If you get too many bubbles, your final product will contain many voids and will be made largely of air!



With the harder fillers, watch them as they set up and do your initial body filing when they're about 80% hard.  This will make your final shaping easier.  If you go too soon or too hard at this stage, the filler will "tear" rather than work smoothly under the file.  Go easy at first until you figure out how much pressure to use.

When the filler is 100% dry, mist on a guide coat of contrasting primer and use sandpaper to do any remaining shaping.

Finally, skim coat any remaining defects, should be very thin coats at this point.  Spray on guide coat and sand it all smooth.

Paint.

Enjoy.

mystic_1

[mystic_1]

Like this: 

mystic_1

[JDHolmes]

We didn't have knee dents, but we welded ribs on the tank and then had to fill and smooth the entire thing.  We started with a couple of layers of fiberglass then came back with Rage extreme and finally, thin polyester fill.  If the dents are over 1/4" thick, do something besides bondo then smooth over it with bondo.

[Industrial Cafe]

Take care with your mixing, both in terms of ratio of hardener, and in the actual technique you use to mix.

Do not stir, this introduces air bubbles.  After you've measured out the hardener into your pile of goo (don't mix too large a batch), take a plastic applicator, and "wipe" across the pile, smearing the hardener into the bondo.  Then scoop up the smeared out pile, fold in in half, and repeat.  It's awkward to describe in words, look for a youtube vid maybe, but the idea is to not introduce air bubbles.

The same technique applies with epoxy resins, btw, you want to take care not to introduce air bubbles.

If you get too many bubbles, your final product will contain many voids and will be made largely of air!



With the harder fillers, watch them as they set up and do your initial body filing when they're about 80% hard.  This will make your final shaping easier.  If you go too soon or too hard at this stage, the filler will "tear" rather than work smoothly under the file.  Go easy at first until you figure out how much pressure to use.

When the filler is 100% dry, mist on a guide coat of contrasting primer and use sandpaper to do any remaining shaping.

Finally, skim coat any remaining defects, should be very thin coats at this point.  Spray on guide coat and sand it all smooth.

Paint.

Enjoy.

mystic_1

that too.

[nvr2old]

I wouldn't really advise using Duraglass or any fiberglass filler.  It's for fiberglass, not metal.  It has a tendency to be filled with pin holes, and it's harder to work.  Fiberglass products don't stick that well to metal.  Rage is a really good filler, designed to be used on metal.  If it's a quarter inch thick, no problem.  Just apply in several thin coats.  Today's fillers are excellent and really should be used.  Using the same product start to finish is safer in the long run, it expands and contracts evenly whereas mixed products kind of compete with each other.

[mrblasty]

Sorry guys but I've got to say that bondo  is absolute junk, it pin holes like crazy, shrinks, and you will eventually get bleed through on your paint  Go to the auto body supply store in your town and buy a can of Rage Gold, it comes in quarts and gallon sized cans, a company called Evercoat makes it.  I've personally laid this stuff on an inch thick and it sticks like no other filler.  It sands so smooth a finish glaze isn't always needed.  Please save yourself a lot of trouble and stay away from the reinforced fillers, they are more trouble than they are worth on a project like yours.  Good luck.

[m511y]

It looks like I'm going to go with Rage Gold. i will keep you posted on how it turnes out.

[Industrial Cafe]

mmmmm, giant cookie!

[Aerobhoy]

some pics would be awesome .as i've just done the same thing with the knee dent's but was unshure about fiberglass/fillers, or just filler.
think i'll go with rage if it's available here in Canada,
jimmy O

[HondaMan]

Where can I get Rage Gold? 

[mrblasty]

Where can I get Rage Gold? 

It's one of the body shop industry standards, find your local auto body and paint supplier, sometimes NAPA has it, if those two options don't pan out Eastwood sells it but they have the highest price I've seen advertised for it.

[Gears]

I just went to the local place called Finishmaster(I think they're a chain) and they stock Rage Gold. It's pricey, about $50 a gallon. Talking to the sales guy, he told that their house brand is actually the same stuff(made by the same company) with a different label slapped on. Cheaper too, so I bought a can of that to try. I'll try and compare it to m511y's picture and see if there's any truth to the claims.

[Flying J]

i used bondo...

[HondaMan]

i used bondo...

Did it shrink? Or, not expand/contract well with the thin gastank?

I'm about to try out the knee-dent thing on a spare K8 gas tank I have left from a cafe' project. I haven't done it in 35+ years, forgot how. 

I don't really need the tank, so it's a good candidate for 'school'. 

[Anti-Johnny]

I hadnt heard of doing this before. I found this video, I guess its the easier part. I am loving this forum more every day. I am learning ways to keep my project bike under my nonexistent budget.

Is this video a good technique for creating the knee dents ?

Id like to see a pic of how something like this looks like afterwards.

The guy only made four videos but in each one he was using items off a cb750. I wish I could find more videos like this. Specifically one on fork seals and carbs. I guess most of us dont have the time to do something too intese like a carb or engine video.

[Flying J]

Here are e few shoots of my tank. Only one side is finished and primed. It has been sittin for a while and the bondo is still there. I guess i bang the tank around a little and see if it cracks. Id hate to chip it all off and start over.

[apex_seeking]

Jees...thats awesome.

[Kong]

That is indeed inspirational.

I use Rage for the little bit of body work that I do.  Actually I use Icing more than anything else, but I don't do major bodywork, just the prep needed for painting, which is what I do.

I can give some general suggestions to others who are going to do this sort of thing.  The first thing I would have done would have been to go ahead and remove all of the old paint from the tank - and I would not have been gentle about it.  In the area where I knew I was going to be doing some work I'd remove the paint with an 80 grit wheel, so that would be where the dent was going to be and the old emblem mounts too.  Then out would come the hammer - and I have to say you did an outstanding job shaping that metal, my hat is off to you.  You can not imagine how much I admire people who are able to do that sort of thing, and of course it gives hope to those of us who are about to try it for ourselves.  Anyway once it was pounded into shape and you've done any welding and grinding you plan to do the very next thing to do is clean it, degrease it, clean it again, and then shoot two coats of epoxy primer on it.  Do not use an 'etch' primer, don't use any rattle can crap, shoot it with the real thing and if you don't have air then put it on with a roller as thin as you can get it.  Then, after you've given it a day to fully cure, then put your Rage, or whatever you plan to use, over the epoxy.  There are many benefits to sealing that tank with epoxy before doing the finish work and no down-side.  Once you've done all of your body work and are down to paint prep give it another sealer coat of epoxy.  Then hit the entire tank with Ice, block sand it, shoot your 2k, block, do your guidecoat, and repeat as necessary, and then shoot your final sealer coat, using exactly the same epoxy that you uses as the first sealer coat, but this time reduce it up to about 10% with acetone.  Then stay within your recoat window and finish.  This will give you a bullet-proof base on which to paint.

A good, and reasonably priced, epoxy to use is PPG's Omni line of stuff.  You should be able to find it in automotive paint shops just about anywhere.