Lead Solder Filling

The article below was something that I was asked to put together by some of the Ford Truck Enthusiasts Forum members to add to a number of Group Tech articles.  I took a classic car restoration course at the Thames Valley University last year and part of the course covered traditional Lead solder filling.

Thanks to Clint Wilcox for being the driving force behind getting the tech articles together and working with me to get this article completed.


Editor's Note: Working with lead is not technically demanding, but does require the fine hand of a dedicated craftsman. 

One such craftsman in the making is our own Lee (Lwlandy ) Progl, who is building a 1956 F100.  Lee lives in the United Kingdom where he is attending a evening course on classic car restoration.  He has contributed the following:

Using Lead as a Filler

Why Lead?

I decided to look into the use of lead solder on my body repairs for a number of reasons:

  1. It was the traditional method used in the fifties when my truck was first produced.
  2. It has much better ductility and strength characteristics than plastic fillers.
  3. I was told that it couldn’t practically or realistically be done these days, which I took as a personal challenge.  I hate these sort of excuses or reasons for not doing something I think should be done.  
  4. I just wanted to have a go at it, to be able to say I had tried it.

When I embarked on the truck rebuild I decided that even though I would be making quite a few modifications over the stock setup I would try, wherever possible, to do things the traditional way and not “bodge” anything.  

I know that many modern plastic fillers are very capable and in some respects are as good if not better than the old methods (especially in the preparation and finishing side).

I decided to look into the use of lead solder.  My research was helped greatly when I joined an evening class on Classic Body Repair techniques.  I would strongly advise an evening class of this type if it is available to you.  You can easily read books (and articles written by recently turned amateurs) but there really is nothing like having a go and being shown how and what to do.

The Materials – Tools and Supplies

To start leading you don’t need a lot of tools or supplies.  I bought a Solder Kit from a restoration equipment supplier, Frost Restorers Equipment.  This company is located in the United Kingdom with a web address of  www.frost.co.uk.  The kit contained all of the items that you need to get started.  It was not cheap at about $90 but contained the following:

  • Solder Paint (Flux/Tinning paste)  This is a combination of lead solder and flux  mixed to a thick paint of paste.
  • Brushes
  • Tallow
  • 2 Paddles, 1 Flat and 1 Curved
  • Flexible File holder and blade (Vixen File)
  • 3 sticks of Lead solder
  • Body Solder book ( About 50 pages containing tips and advice with quite a few photos)

In addition to the kit contents you will need a heat source for melting the lead, some water (for cooling) and some rags.

The lead solder supplied in the kit did not have any identifying marks on it but I believe that it is a 30/70 mix, 30% Tin to 70% Lead. This is the usual body solder composition. Pure lead melts at a very specific temperature, whereas a lead/tin alloy melts over a given temperature range with a solidus stage.  This is when it is not yet a liquid (Liquidus) but is at a stage where it is plastic, and can be manipulated and spread. 

I started by using an oxy acetylene torch to heat the areas being leaded, but soon changed to a MAPP gas torch.  The MAPP gas torch has a much gentler and wider heat spread, which is what you want when leading.  If you use an oxy acetylene torch, you should use a slightly carburising flame, i.e. one that does not have as much oxygen as a welding flame.  This flame will be blue with no yellow.  This will give a softer more controllable heat.  It is also possible to use a heat gun, such as used for paint stripping etc.

The rags and water are needed to cool the area being worked just after applying the lead, this helps prevent over heating and warping. 

Applying – Laying on the Lead

This is not a definitive guide, but is the way that I have found that works for me.  It is based on the tips and advice from the book included in the kit and also what I picked up at my evening class. 

Cleanliness is key - Before you begin, make sure everything is clean!  

Before you attempt to start spreading any lead you must make sure that the work piece is very clean and free from anything that could contaminate the lead solder, especially oil or grease.  The flux will do a good job of cleaning the area, but it will struggle if the area has not first been degreased and cleaned back to a shiny surface.  

Here you can see the front fender cleaned off just prior to working on it.

Fluxing (Tinning)

The kit contains a combined flux, solder, and tinning paste that you paint on to the area being repaired with a brush.  There are various other methods of applying flux and tinning such as powder and liquids but this is what my kit used.  The paste cleans the area to be worked and also "tins" the area with a thin coat of solder, which helps the bar solder adhere to the panel. 

Using a brush, paint the paste over the area being repaired plus a couple of extra inches to allow for feathering the edges.  

After painting the area with the paste, apply heat with the torch in a careful manner, gently moving the torch around the work area so as not to overheat any one portion.  When the flux starts to run clear you are near the correct temperature.  With a bit more heat  you will see the solder start to bead and melt.

At this stage the idea is to ensure a good coverage or "Tin".  This is done by wiping the area with a cloth to spread the solder and remove any excess.  Essentially you wipe the area to get a nice shiny covered surface or "wet the surface".  Any pitting or blackened areas indicates the area has not been cleaned sufficiently and you will have trouble applying the lead.  When this happens, the best thing to do is to clean the area again.   Remove all excess solder by wiping it off with the cloth.

Applying the Lead

The easiest way to apply the lead is directly from the bar.  You apply heat to the end of the bar and also to the area that you have already tinned in order to get them both to a similar temperature, which is just about the plastic stage.  When the lead bar is about to the correct temperature it starts to shine.  At this point you want to push the end of the bar onto the panel and effectively crumble the required amount of lead onto the work piece.  It is important that the tinned area is also heated to a similar temperature so that the bar sticks to the repair.  Otherwise it would simply fall off of the work piece.  Once you have the required amount of lead stuck to the work area it is time to start to spread it.

This picture is me applying the lead to the fender. 

Notice how clean the fender is, and the less shinny area around the lead bar.  This is the work area that I have tinned.


You spread the lead using wooden paddles or a leather moleskin.  The paddles come in a variety of shapes and sizes, but I have found that the flat paddle is the one used the most.  

You prepare the paddle by heating the tallow until it is molten, then wipe the paddle surface in the molten tallow puddle.  This will prevent the lead from sticking to the paddle. 

At this stage you need to heat the lead on the panel to the correct temperature for spreading.

In this picture I am spreading the lead with a paddle.  You can also see the patches of solder paste/flux in the other areas to be repaired.

The best analogy for the consistency of the lead is that it is like peanut butter.

Imagine what it is like to spread peanut butter on your fender using a wooden knife, which is what it feels like.

The lead starts to go shiny when it is the correct temperature.  You need to alternate the between applying the flame and using the paddle to supply just the right amount of heat to keep the lead at the consistency to spread. 

There is no need to be ultra neat as you can always file off the excess.  More is better as if you put on too little solder you will have to start all over.  Unlike plastic fillers where you just apply more putty over the top of the already worked area if it is still low, with lead filling you only have one chance to get it right. 

This is because when applying more lead on the top of the existing lead you melt the existing lead, which then requires the entire repair be reformed.  This can be very frustrating.

Once you have spread the lead over the area being repaired, you should wash the area with cool water to quench the area and also remove any traces of flux/tinning paste.  This paste is very acidic and can cause problems with the automobile's finish.

In the picture to the left the lead has been spread over the dents and is ready for finishing.

Finishing – getting it right

Finishing is the hardest part of the process because lead is a lot harder to work than conventional plastic filler materials.  In addition, the finishing of Lead is a manual process rather than an automated one as it is with plastics.  This is a health and safety requirement as lead filings in the air are very harmful.  Grinders and electric or air sanders should never be used on lead patches.  

The general process once the lead is applied is to rough file the area with a Vixen file.  This is a flexible file that you can adjust to have either a concave or convex shape according to what you are finishing.  

It is very easy to get it wrong with the Vixen.  You must try at all times to keep the file moving in a straight motion, if you let it move in a sideways motion it tends to dig in and cut grooves into the lead, rather than shave the surface off smoothly. 

I found that I had to practice a lot with the finishing, I found myself working on the same are 3 times over, all down to me being over zealous when removing material.

After roughing with the Vixen you can move to conventional files and continue to remove material to the point of finish sanding.  Then it is just a matter of priming and painting.

Saving Lead

It is a good tip to catch all of the lead filings that you create when finishing.  This is because lead can be reused. I found that laying a piece of card or paper on the floor to catch the filings helped.  You simply put the filings in a metal container (known as a mush pot) that can then be heated to melt the shavings down again for later use.  You melt the lead in the mush pot and then pick it up with a paddle to spread.  


Use good common sense when working with lead.  Avoid ingesting lead filings by always washing your hands before eating or smoking, do not eat or keep food near the work area, do not put your fingers in your mouth or touch your lips or nostrils.  Do not rub your face with your sleeve or other parts of your clothing. 

You should work in a well ventilated area, avoid overheating the lead, and vacuum your work area instead of sweeping it.  The most important safety tip is to hand sand only, never power sand or grind lead.

Enjoy your Work

I really enjoy working with lead.  No small part of the enjoyment is to see the looks on the faces of the young guys at the workshop when they see me spreading the lead.  They have never even heard of lead filling, let alone seen it before.  The next time you attend a car show or car club meeting just mention that you leaded in the seams on your ride and watch the reaction of the people around you.

It makes whatever extra work leading requires worthwhile.

I do hope you find this article interesting and informative.  If you have any questions I am available either by email or on the 48-60 forum.  I am more than happy to help any way that I can.

However, lead work is one thing that can not really be taught, you have to learn by doing.  So just jump in and get started!