How To Repaint A Car – Part Three – Dent Repair

Our project VN Commodore is finally back in the garage and ready for some straightening and painting.

Repairing Dents
In this part I would like to talk about dent repairs. Our Commodore is reasonably straight with only a few ‘shopping trolley’ dents that need to be repaired, however the methods used here can also be applied to dents of a reasonable size.

How To Paint A Car

Please note that I am neither a qualified Panel Beater or Spraypainter and my methods may not be ‘technically’ correct but I have been repairing and re-painting cars for more than ten years and these methods are what I have found the best, for me anyway!

Where To Start?
Ok, first things first, we need to find out what we are up against. If you want to do a really good job of straightening and painting your car you need to find each and every dent, mark or scratch that will stand out once the nice glossy top coat goes on.

If you have some panels that have many dents or large dents that may have stretched the metal I suggest you search for a replacement if possible. There are ways of repairing large dents however it is a skill that needs to be developed and is beyond the scope of this DIY guide.

The first thing I suggest is to give the car a thorough wash so it is easier to spot any problem areas. The next step is to inspect each panel, one at a time, first by eye-site and then by running your hand across the panel. My choice is to have the car inside when doing this, however the lighting needs to be good. You also need to position yourself in a way that any small dents are seen. For instance, when looking at the doors, crouch down beside the car and when doing flat panels your line of sight should be along the same lines of the panels.

Going over the car twice even three times is a good idea so you don’t miss anything.

Once All The Dents Are Found
There may be some areas where there is a collection of small dents close together that you would like to repair, such as along doors and quarter panels and we will look at what I think is the best way to handle these in Part Four (coming soon, real soon!).

Next we have to figure out the best way to repair each dent. The ideal way is to ‘panel beat’ the dents out from the inside and finish them off with a smear of body filler. This is not always possible and for the most part the type of dents that the garage handyman (person?) would be repairing body filler should be a suitable solution. I don’t suggest using copious amounts of body filler to fill large dents though as it will crack if used too thick and large areas of body filler are hard to get straight and usually look pretty ordinary. If you can get behind the dent and use a hammer and dolly to get the majority of it out that is a bonus and obviously reduces the amount of filler used.

Repairing The Dents Using Body Filler
The first step in the dent repair process is to remove the paint in and around the dent area. For the small dent in the pictures I used 80 grit sandpaper by hand, however any sanding method will do as long as it doesn’t gouge into the metal.

Time to mix the body filler. I have used a Corolla rear quarter window for years to mix the filler on. Pretty high tech I know, but I have found it to be the easiest thing to clean and you can easily mix up some filler and take it with you as you go around the car. Also I have become very attached to a certain paint scraper. I find it heaps easier than the usual plastic things they give you to apply the filler and as you can see it is nice and flexible to follow the panel lines.

Most body filler is mixed at 50 to 1. A little trick a panel beater told me was to think of the filler as a box of matches and the hardener as a match. Two matchboxes of filler, two matches etc etc . Once thoroughly mixed it should be an almost-pale pink colour. A redish colour indicated too much hardener and it will probably harden before you get to apply it, a very-pale pink indicates not enough hardner and you will be waiting forever for it to harden. Getting a good consistency and knowing how much to mix for each dent takes practice but it will become easier as you go. When mixing the filler be sure to ‘force’ the two parts together to ensure that it is thoroughly mixed and any air bubbles are removed.

The way I apply the filler, once again this is only what I find best, is to first apply the bulk of the filler to the dented area and then smooth it out following the contours of the panel. Once the filler is distributed around the area I then go along and smooth it all down. Applying firm pressure to the spatula or paint scraper usually gets the best results. Be sure to extend the filler further than the edge of the dent so you can feather the edge. On a small dent I suggest taking the filler about 30-40mm out around the actual dent area and for larger, deeper dents you can double or even triple this.

Once the filler starts to harden(5-10mins), even if you haven’t finished smoothing it down I suggest leaving it and applying a thin layer of a freshly mixed batch. Sometimes it will ‘ball’ up and ruin the whole surface if you try and smooth it when it has started going hard. If the dent is reasonably deep, ie more than 15-20mm I think it is better to build up the filler with a few applications rather than trying to fill it all in one go.

Once The Filler Has Set
A handy tip I picked up is to run a razor blade across the surface of the filler before sanding. There is usually a layer of wax type material on the top of the filler that clogs the sandpaper in no time and the razor blade removes this and any ridges in the filler and saves your sandpaper.

The only tool I use for sanding body filler is pictured below (with broken handle and all!). There is a name for this tool, it just escapes me at the moment! Speed File, yeah that’s it. These are brilliant for straightening panels as their long surface area ensures that you are sanding along the same original contours of the panel.

Use a sanding block or orbital sander is really hard because they have a tendency to pitch up and down with the surface of the filler and not follow the true lines of the panel. Sure a bit of elbow grease is needed but the results will be so much better. I usually start off with 80 grit paper and once the filler is pretty close to flat I switch to a finer paper and then a final hand sand with 600 wet and dry, used dry.

If you find that you have some low areas, indicated by ‘un-sanded’ areas of filler now is the time to apply some more to those areas.

Once you are satisfied that the repair is up to scratch, pardon the pun, it is time to lightly sand the rest of that panel, being sure to remove any remaining sanding marks and move on to the next section. More to come…

Part Four can be found HERE

9 thoughts on “How To Repaint A Car – Part Three – Dent Repair

  1. Thanks so much for your advice! My husband and I are considering respraying my mum’s much loved JE Camira after it was scorched on the left rear panel by a fence fire. We’re still getting educated before beginning the task and are very much novices, but this has been so useful. Thanks again 🙂


  2. No worries El, glad you found the articles useful. I have a few more articles to do to finish the series however I am having a lot of back trouble at the moment. Fingers crossed the rest of the articles will be up in a week or so.


  3. G’day Craig,
    Do you have any advise about the type of body filler to use? Is the stuff from the local auto supply shop OK (Supercheap, Repco etc) or should I try to get something better from a dedicated Paint shop?


  4. Hey Glenn,
    The filler used in most panel shops is the same stuff that you can buy from Repco, SuperCheap etc, except that they usually buy it in a 20 litre drum! From what I’ve seen K&H brand seems to be a popular choice among panel beaters.

    Some advice that I was given many moon’s ago while working at The Bump Shop was that all brands of body filler can suffer from ‘shrink-back’ which is, obviously, where the filler literally ‘shrinks’ over time and the ‘thicker’ it is applied the worse the shrinking effect. I think with a project like your’s this shouldn’t be much of an issue though as it looks like the amount of filler it needs will be minimal and any shrinking should be evident by the time you come to applying the top coats. If you were talking a couple of days turn around between bodywork and finished paint work it may be a different story but I imagine it will be a bit longer than that.
    Also we were told to ‘kneed’ (is that even a word?) the filler well before adding the hardner to remove any minute air bubbles in it. The more air you remove the less shrinking is likely to occur.

    Hope that all makes sense.

  5. Thanks Craig,

    I think your right about it being a time consuming process?which leads to me next question…
    I can see from some of your photos that areas of bare metal can be exposed around the repair site. How should I address this? Obviously I can?t leave the bare metal exposed while I spend days or weeks working my way around the body shell. Should I spray something on to seal the repair site?i.e. primer???
    I?m guessing you?re probably going to say yes?if so, should this sealing coat be a good quality primer (mixed up and applied with a spray gun) or will a rattle-can of premixed primer from Supercheap serve as a suitable temporary sealant which could/would be rubbed off later, prior to spraying the main primer coat?

  6. Glenn, normally I would suggest a can or two of primer or spray putty (depending on whether or not you want to wet-sand the finished product) HOWEVER given that both of these are porous and don’t provide great protection against moisture and given that (I imagine) it is likely that it will stay in primer for a while I suggest looking at better alternatives.

    One would be to apply a primer to the finished area and then a top coat or two to ‘seal’ it up and when the time comes for the top coats sand through the existing top coats and re-primer the whole thing etc, etc. Bit of a pain in the bum.
    Or I did hear not so long ago that someone had released a product for this exact application. It was a primer/putty that was non-porous and you could leave the panel/repaired area coated with this stuff for as long as you like without fear of moisture attacking the surface underneath and it was compatible with a number of different top coats. I can’t remember if it was available as a spray can or a spray gun would have to be used.

    I may have read it in Street Machine or one of those type mags. I’ll see if I can find the article when I get some spare time (ha ha flippin ha!). In the meantime a call to a automotive paint supplier may point you in the right direction. If you explain what you are doing and are looking for a water/moisture proof non-porous primer I’m sure someone would have heard of it. Either that or I dreamt it in one of my pain-killer induced nightmare’s! Just kidding, jeez they send you off with the fairies though.

    Hey thanks for the photos you sent over on Tuesday, I’ll post them up and a bit more info as soon as I get a chance.

  7. No worries Adam. If you do get stuck on something that is not in the articles don’t hesitate to shoot us an email. I’m no expert but I will do what I can to help you out.

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