I have never done a tutorial before, and today it occurred to me, that as long as I’m doing the same things over and over, I may as well document some of the steps on the off chance I can help someone else doing this..
Using JB Kwik Weld for filler just happens to be the one step I haven’t screwed up on my Outlaw project, so I’m going to show how I use it to fill the gas fill opening.
(Which happens to be giving away one of the *secret* modifications I’m doing to my custom 356, but at least I get to show that something has gone right in this longer-than-it-should-be journey.)

My materials are a freshly stripped Porsche body, the 2 tubes of JB Kwik Weld, a half round needle file, sandpaper, toothpicks, and some scraps of cardboard on which to mix the filler. I have what I call hard and soft sandpaper. The hard is brand new never used stuff, the soft has been used and is, well, soft. Comes in handy later.
I use old business cards for mixing. Use whatever you have. You can also use the *regular* JB Weld, your choice, but it takes longer to reach the final set, or hardness.

This is a small hole to fill, so I don’t need too much of the JB Weld, but I do need to have equal portions from each tube, or as close as I can get by eye. This is more than I really needed, but I wanted to make sure it was visible in the photo.

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Mix the two parts together with a toothpick or anything else sturdy enough to do the job. Mix until it’s a consistent grey color, if you see any streaks, keep mixing. Have the subject cleaned and ready to go as the working time of the mix isn’t too long. I used a half round needle file to clean the insides of the opening, and lightly sanded the hood around the gas fill opening. It’s not open heart surgery, so don’t go nuts, just clean it up and wipe off the dust.

I’m starting application from the underside of the car, using a small piece of card stock as a backer on the hood side and holding it in place with my finger as I apply the stuff.
Fill the hole, using plenty of the filler, there will be a little time to wipe some of it off.

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As I remove the card backer from the hood, it pulls some of the filler up above the surface of the hood, which is what I want. This insures that the entire opening is filled on both sides. Otherwise, I will have to mix another batch to fill in any areas that harden below the hood surface. (I have used more than needed, as I mentioned, but I am trying to be clear about my process.)

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Make sure to keep the filler AWAY from the hood lines, or you’ll be starting over on another body. The excess hardened filler has been known to just break off the body cleanly at times, but it’s very rare, usually from not cleaning it properly, and you can’t count on it to separate from fine details like the hood lines. Tape it off if you need to.

The directions on the tube say it SETS in 4 minutes, but I give it a lot longer so I don’t fill in the teeth of my file with semi hardened goop. It actually takes hours to fully CURE, meaning reach optimum hardness, but you can start to sand and shape it before then.
Go make a cup of tea and go through your email while you’re waiting.
The JB Kwik Weld will dry/cure to a shiny dark grey color. You can also start to do other body work while it sets. I started to file down some of the mold lines while I waited.

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I tape off EVERYTHING as I work on it!

Once it has set for 15-20 minutes, or enough to start working it, I can start to remove everything above the hood surface. If I’ve left a substantial lump above the hole I’m filling, I can take an xacto knife and carefully carve off the bulk of it, being careful not to carve the car. I try to remember to surround the area I’m working on with masking tape, so that even if I slip, I only tear the tape. At this point, the filler is still soft enough that you can carve it rather easily, so be careful.

After I’ve removed as much as I can with the knife, I start filing the top of the lump to bring it close to, but not all the way, to the surface of the hood. Patience is key when removing hardened filler. I don’t want to even touch the bare metal with the file if I can help it, to avoid scratching or gouging the soft zamac alloy.

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Once I’m reasonably close to the curve of the hood, when it’s almost all light grey, I switch to sandpaper. I start with the hard, or new, sandpaper to get the bulk of the sanding done. I’m using 220 grit paper. You can use a finer grit, but don’t go much coarser or you’ll leave lines across the hood and the filled spot. I will have replaced the masking tape several times by now, while working with the knife and file, and I’ll replace it again with fresh tape before I start using the sandpaper.

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A fresh layer of tape lets me see immediately if I’ve sanded too far or torn the tape over a detail I want to preserve. Old tape gets the zamac dust all over it and sometimes it’s hard to see if it’s torn. Tape is cheap, the time you’ve spent getting to this point is the thing you don’t want to go to waste. And by continually changing the tape, you can judge your progress and see how far you have to go.

If you’ve left a large lump on the underside, you can trim that back or leave it alone if it’s not in the way during reassembly. I will grind these down further with a dremel tool when it’s time to assemble everything again.

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Try to keep the sandpaper centered on the bump of filler so you don’t start taking metal off the body. Take your time, sand back and forth from different directions, as well as in a circular motion, so you’re sanding it evenly.

Here you can see I’ve slipped and barely nicked the tape covering one of the windshield wiper nubs, but I nicked it hard enough to make the nub shiny, which means I’ve removed a tiny bit of metal, so I put more tape over it.

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You will start to see the outline/shape of the filled opening appear in light grey against the shiny metal color. By now you should be sanding with no tape, “soft” sandpaper, and extra caution around the hood lines. When you get down to the hood, you will have the exact shape of the opening in filler color. You may be tempted to go just a little more, but STOP! Otherwise you are removing metal from the hood as well as filler, and creating a depression that will need to be filled again. Once you’ve lost that original round shape of the filler opening, you’ll never have it back as an indicator that you’ve reached the surface, and you’ll be sanding oval shapes and it will be hard to get it right again.

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Here is the finished car, on the left, next to a couple more that have been filled and the mold lines sanded down. There is still some tape on it because I’m not finished sanding. I’ll start on the rest of the mold lines next.
If it makes you feel more confident, practice on a junk body first until you are comfortable with the file and/or sandpaper. Practice filling different size areas, drill holes if that helps, and fill them back up.

Clean it very well, with compressed air if you like, to get all the dust and metal filings out of the details and off the surface. You can wipe it with a toothbrush and chemical cleaner if that’s what you’re used to using for paint prep. When all the filling is finished and the mold lines filed down, and cleaned thoroughly, it’s ready for paint.
Thanks for being so patient and reading all the way through. As a reward, here are some photos of the engine lid being masked so I can file and sand off the louvers on the sides. Look again at the photo above, of the three cars side by side, for a better look at the finished louver removal.

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Always tape much more than the area you are working on. You’ll be concentrating on that one little spot and not paying attention as to where the other end of the file is as you’re working. As I said, tape is cheap and it can keep you from gouging the body or filing into fine details. I probably used a good 18" of one inch wide masking tape doing this one body. Doesn’t sound like a lot until you realize I cut it into little pieces as I use it, and I change it often...it goes fast.
If I ever get halfway decent with a rattle can, I’ll document the painting of one of my cars, but don’t hold your breath!
If I’ve used up too many words pointing out the incredibly obvious, when the merely obvious would suffice, let me know in the comments so I can dial it back if I try this again. Thanks for reading, and good luck!