Fast way to get rid of Bondo?

[dbrick]

I would agree with Sid, The old rustproofing companies drilled 3/8 holes all over the place and plugged them. Better to get all the stuff out and get it coated. Adding a drain hole to any closed cavity would be a good thing to consider too.

[garth]

Something you also might want to consider during restoration is coating the inside of your doors, as none of six doors we looked at had any coating beyond the original primer. Water getting past the window seals is intended to be drained through some small vents at the base of the door and this is where most of the rusting originated from. Both my donor and my original car doors were pretty banged up and after chemical stripping all four we decided to purchase some NOS doors. Even the inside of the NOS doors had some surface rust on the primer. Remedied by bead blasting the insides to bright, baked, primed, then coated with a final color coat with an elastomer additive.

As a preventative measure, annually removing the door panels and blowing out the debris from the drain vents will help. Might be overkill in the drier climates but not here on the wet coast.

[ttyR2]

While waiting on various engine parts, I started removing the bondo that was in various places on my car. I used a wire wheel (straight bristles, not the knotted kind) in a 4 1/2" grinder and it cut through the bondo like it wasn't even there. If I'm careful, it doesn't groove the steel bodywork much.

Being as how I'll have to fill in some of those scratches, I'm curious if a high-build primer is the "correct" thing to use. Is it any more likely to peel or flake off than a normal good quality straight primer? Are there any drawbacks to using high-build primers? My plan is to use lead to do any filler work, and avoid bondo all together. I'd probably use a two-part glaze to spot fill pinholes and the like (not the one part glaze-in-a-tube stuff).

[EScanlon]

The wire wheel method is excellent... except for the mountains of dust/debris it generates.

3M also makes some sanding discs called Roloc that have various grits as well as the scotch pads. One of the items that can mount on the Roloc is a "finger" brush of hard abrasive rubber/plastic. To my knowledge, it's available in two styles, green and yellow. Both of those are very good in removing bondo like the wire-wheel, but much gentler on the surface metal. In fact, used carefully they're excellent as a "pre-polish" on rough or pitted metal. (http://solutions.3m.com/wps/portal/3M/e ... BKJFSK8Ggl" onclick="window.open(this.href);return false;)

As far as filling your "scratches" with primer or high-fill or glaze (aka icing), that's something that only you can determine.

Several coats of light fill primer, if applied sequentially before the previous coat "skins", can be done, but then you need to wait (or use infra-red or an oven) to cure the piece and allow the primer to shrink. That's why they came out with High-Fill, to do it all in one or two steps.

Applied properly none of the primers should give you a problem. Biggest drawback in using any of the primers is the time to allow the primer to evaporate all of the solvents and shrink. This can be the biggest problem as people get impatient. Even when wet-sanding the primer, afterwards you should allow some time to allow the primer to dry out properly.

If you ARE knowledgeable using Lead as a body-filler substitute (the original) then go for it. It does add weight (a LOT) but it isn't porous and it's use as a body filler is known.

However, if you haven't ever worked with it.... it might be a bit of a pipe dream. Aside from the many different paddles, rosins, files, shavers, brushes, fluxes and torches you will need, you then need to master it's use.

Proper use of metal bumping techniques, followed with the proper use of polyester filler (aka Bondo) and you will effect the same result. Most of the time, filler gets a bad rep due to inexperienced workers slapping it on as if it were the fix-all of body work. Sometimes the slightest amount of metal bumping can almost eliminate the need for body filler and allow you to use filler primer instead. As an aside, NEVER drill holes into the metal to get the polyester filler "grip better". Those little "worms" on the back side of the metal usually crack/break off and then there is direct contact with the atmosphere and humidity to the bondo. The end result is rust.... from underneath your repair.

The two part glaze you mention (sometimes referred to as Icing), as well as the one part (sometimes known as Red-Cap), is typically used to fill those minute scratches and pin-holes that can creep into the repair. I've seen filler mixed such that it actually had bubbles in it that "popped" when you began to sand. Those need to be filled. Icing is quick to mix, fast to sand, and doesn't shrink much. Red-Cap is notorious for shrinking hours, days and even weeks later... after the paint has set. Don't take this to mean that Red-Cap should never be used, just that it should be used very sparingly.

So, which one is correct for you? Well, as you can see, it depends on how "deep" those scratches really are.

Mild scratches and shallow dents... primer may take care of it, or you may want to use high-fill primer.

Deeper scratches, dents and creases will probably require body filler. Lead if you're experienced with it, just don't breathe in the dust, otherwise Bondo will work well.

Deeper dents, and serious creases should be "bumped" first, then when the damage has been minimized, apply the filler needed.

FWIW
E

[datsunrides]

^^^^ All excellent points! ^^^^^ I may add, make sure to use either an etching primer or epoxy primer as a base on bare metal before you start in with the fill and sand primer. I tried lead once. I can make it work pretty good on horizontal surfaces, vertical, forget it! Professional quality filler is very good and much easier to use. Red Cap sucks! Use icing.

mark

[wilrobasy]

I used a butane gas tourch and a scrapper.
Mask and goggles a must as it is pretty nasty stuff.
but just melted and scrapped off the bondo without damaging the metal underneath.

the hit the affected area with my portable sand blasting kit to clean it up before working on the repair