How To Paint A Car – Rust Repair With Body Filler

Today we are looking at what is involved in repairing rust with body filler. It is my opinion (hey, I’m a mere grease monkey and not a panel beater so please keep that in mind) that only the smallest rust affected areas should be repaired using this method. If you want a lasting repair or the rusted section is bigger than say, a 10 cent piece, I recommend cutting out the affected area and replacing it with new metal, which we cover in a future article.

How To Paint A Car

Ok, as you can see the tailgate on our Laser (should I say “ASER”, don’t know where the “L” got to) has a few sections that have rusted right through.

how to paint a car

how to paint a car

The first thing we did was remove the trim from below the back window. I’m a big believer in removing what you can rather than trying to work around it, for the small amount of time it takes to remove a piece of trim or a light etc it can make the job look a whole lot neater.

Next up we ran a heap of masking tape around where we would be grinding and sanding. Doing this helps to avoid damaging windows, trims, badges etc.

how to paint a car

The next step was to grab the angle grinder fitted with a wire wheel. Remember to always use eye protection with these babies!

how to paint a car

With the wire wheel the idea is to remove as much of the rust as possible and also remove the surrounding paint until you have a good area of clean metal around the rusted section.

how to paint a car

As you can see those two small rust holes on the left hand side turned into quite a hole! What I do now is grab a ball pein hammer and knock down the edges of the hole so that there isn’t a ‘hard edge’ to fill to, rather it is more gradual. Doing this makes the edge a lot easier to sand smooth and you won’t have an obvious edge that will show through when painted.

Next up is coating the area with a rust converter. The rust converter we are using is a Septone product. This is brushed on, left for 15-30 minutes (time to react with the rust) and then wiped down with a damp cloth, followed by a cloth with methylated spirits, and finally wiped clean with another cloth. I’m not sure if all rust converters are used in this manner so please follow the instructions that come with the product you buy.

Once treated, any remaining rust will usually turn black. Although our metal looked fairly clean after the wire wheel treatment from the photo below you can clearly see that there was still rust present.

how to paint a car

Now we can begin to cover the areas with body filler. We were able to stick some masking tape behind the holes in our tailgate so that the body filler wouldn’t fall through. Obviously you can’t do this with every repair and it might take a few mixes of body filler before you are able to build it up enough. The tape isn’t pressed hard against the under-side of the area, leaving it a bit ‘loose’ allows the filler to seep around the edges and hopefully provide a stronger ‘bond’.

how to paint a car

I picked up a really good tip for mixing filler from the Spray Painting & Panel Beating DVD Course that we advertise on this site. Lay out the amount of filler you think you will need and then run a bead of hardener across the filler like so -

how to paint a car

Obviously it’s not an exact way of doing it, but this will give you a mix that allows a good 5-10 minutes of ‘working’ time which is good for smoothing it out once you have initially applied it. Once you have it mixed to a uniform colour it is time to apply it to the prepared areas. Personally I am yet to master the fine art of applying body filler, it usually takes me two or three applications before it looks anything like the surrounding areas!

how to paint a car

Another great tip I picked up from the DVD Course is once the filler has set, go over it with a cloth soaked in thinners. What this does is remove the ‘film’ that builds up on the surface of the filler, the same film that usually clogs your first piece of sandpaper!

Once our filler had set and we’d wiped it down I roughly shaped it with 80 grit sandpaper used on a sanding block. When the filler was close to the shape we needed I switched to 180 grit paper, again used on a sanding block.

how to paint a car

how to paint a car

Now it’s time for some primer and colour coats. On repairs of this size a spray can of primer and a can of top coat would be all that is needed to finish it off nicely, just be sure to mask anything you don’t want to get paint on! 

how to paint a car

If your car has a clear top coat (most metallic coloured cars and cars from the mid-80′s on) you can also buy clear coat in a spray can to help match the new paint to the old.

As the paint on the bottom area of our tailgate is pretty ordinary we decided to repaint it and attempt to ‘blend’ the new paint with the old up the sides of the rear window. The area we are going to repaint was rubbed back with a used piece of 180 grit sandpaper to provide a key for the new paint and we will be using a primer surfacer and then a spray can of the car’s original colour. I will post the result, if it turns out ok!

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5 Responses to “How To Paint A Car – Rust Repair With Body Filler”
  1. Rust Guy says:

    Great article! It’s obviously taken some time to write & add all those pictures so just wanted to say thanks for sharing.

  2. Barry says:

    Yeah, thanks.

  3. sera says:

    thanks for taking the time to do this – it helped me out enormously & saved me £££’s

  4. PJs Panels says:

    Great post Craig! If the defect is a scratch, determine if it extends below the surface of the paint and into the primer. Sometimes one end of the scratch looks fine but the other end gets deeper and deeper until it breaks through into the primer and the metal underneath. How much of that scratch is below the color? If it’s a small portion of the entire scratch, you may want to repair what you can, and just try to ignore the rest until you’re prepared to repaint the panel.

  5. Thanks for sharing the article. Its very important to the maintenance of the car. Sometimes scratch looks fine but if the scratches gets deeper and deeper until it breaks through into the primer and the metal underneath.

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