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How to - Fixing a rust hole that's rusted through the lower 1/4 panel - With Pics

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I thought I'd chuck this together quickly, as I know the Mk3's suffer with the rust bubbles on the lower doors and 1/4 panels.

Anyway, Over the weekend I've decided to fix the rust bubble/hole that had rusted through letting all the water inside the car. Everything I did was using any-day household tools and cans of spray not a compressor.

I did forget to take a before picture, but believe me it was terrible! A circle bubbled up mess with a big rusty hole in the middle!

First of all I had to grind out all of the rust, I did this by using a normal 110mm angle grinder with a metal grinding disc. Going very slowly I sanded back a square around the hole. The rusted bit was very bad so had to grind down until there was shiny metal and all the rust had been ground out.

After doing this, the metal on the wing is super thin and not workable. The next step was to get a metal cutting disc and cut out a rough square in the 1/4 panel, which cuts all the remaining rust and metal that's useless away. I then slid a metal plate in from inside the car and just held it in place for a minute. This is what I was left with at this stage:


The next step was to weld the super thin 1/4 panel to the metal plate from outside the car. The panel metal was so thin that it was horrible to weld and even on the lowest setting it was easy to blow holes. Either way I soldiered on and after doubling up and filling in all the holes, this messy weld is what you're left with.


It's now time to grind it back, because the metal plate is behind the panel, nothing protrudes from the panel, so grinding back as much as possible without damaging the metal is a good idea. Here is the result.


Now, the next bit is the body filler bit. However it seems I forgot to take any photo's as my hands were just white. Apply the filler in small amounts, and sand back using a flat block. Using you're hands will result in a rippled finished panel, which you don't want. Don't rush this step as this will make it look great, or crap!

After a few hours of sanding and applying to build it up to it's finished standard, you can start thinking of paint. I started by masking off the square, wiping everything off with panel wipe then over with a quick layer of grey primer, and a quick layer of paint. After this dryed, I sanded it down with 800wet dry with warm soapy water. This was the result.


After sanding down the rest of the panel, and masking everything off properly, it was time for the primer on the whole of the lower 1/4.

Started with this...


1st layer on nice and thin, wait between layers and wiping everything off with panel wipe before spraying anything.


2nd layer


And finally 3rd layer.


After a quick going over with some 1200 wet dry, and some more panel wipe it was time for colour.

Obviously spray cans aren't the best, but this shows exactly what you can do with them, and a lot of patience! With a layer of black on looking like it's stone chip! You think to yourself how can this possibly look any good!


when that was tacky, another wipe over with panel wipe and a 2nd layer was lightly put on on top.


Then comes the boring and very careful job of sanding the fresh paint down so it's all flat. Again it takes ages, and have to be very careful with the fresh paint. I used a 1500 wet paper and again with a flat block to do this.

After this is all done, yet more panel wipe, and time for some clear lacquer.

The 1st layer goes on and it doesn't look all that brilliant. I had a small halogen heater by the panel just so it was a bit warmer to spray, and hopefully make it dry a bit quicker without blowing dust onto it. The result of this...


another coat after that,


After that had dried for at least a few hours, I could then sand it down until all of the 'orange peel' was out of the lacquer, again, unfortunately I didn't take any pics with my hands being so wet and dirty. Again this was a super careful job, using 1500 again with lots of water until the panel was completely dull.

Now it's time to mop the panel to the finish you want. I use a very light compound made by 3M called Finesse It. I've used it many times and think it's brilliant stuff. On setting 1, keeping the mop moving all the time, slowly buff the panel up to a shine.

So there we have it, looks like new!

Here are a few end result pictures.




All I need now is some nice new sill covers as this one has separated away from the metal backing!

Considering it's all done with spray cans, I can't complain about the finished result. And at least now I don't have a huge rusty hole in the side of the car! Hopefully this might inspire a few people to have a go themselves, however you do so at your own risk ;)

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Thanks for all the good feedback everyone.. i know myself how much help these little how to guides are from when i did my timing chains. only takes a post like this to give you the confidence to have a go yourself.

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i take my hat off to you ..  rattle cans arent as bad as people make out ..  bodywork is 95% prep as youve shown .  do you run the hobby mig on gas or flux wire? i have a lovely 275 super mig and its great for thin stuff on the lower settings but i agree its an art ..  pannel rip from heat-sink is a common sight ..  

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