The "art" of Lead LoadingI've updated this page on 1st March 2006 to reflect new information I've gathered.
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Just to be sure we know what we are discussing here, lead loading is also known as "leading", "body solder (ing)" and "wiping metal". These names all refer to the same thing in different countries.
Lead is the old, traditional method of finishing car bodies, while plastic filler is relatively new to the game (40 or so years!). Unfortunately the art of lead loading has died out to a large extent as everyone reaches for the quick, easy, -- no skill needed -- plastic filler. There is also concern about continued use of lead causing a build-up of toxins in the user's body. However, since we will only be doing a few hours worth of working with lead as against a 30 year career in the panel beating business, I think we are relatively safe.
Advantages of Lead
Lead is waterproof, while plastic filler is not. So if you are working on a car over a long period, you may wish to consider using lead rather than plastic filler. If you plastic fill and leave it without painting it, it will gradually absorb moisture. Priming is not enough. I've spoken to several paint manufacturers who state that primer is NOT waterproof. When you do come to paint you will have potential problems from the moisture content within the filler.
Lead will also "bridge" small holes in the metalwork. By small I mean small, not holes you can get your fingers into…Use some common sense here!
A section of a practice door. The lead repair to the right shows signs of needing more lead, as there are some depressions which have not been filled. The hole at the bottom, left, could be cleaned up, and if the remaining metal is sound, could be "bridged" with lead.
Materials
The lead used in lead loading is actually a mixture of lead and tin. The required proportions for motor vehicle work are 70% lead and 30% tin. This sort of lead has a melting point of about 500 degrees F. Remember these proportions, as you may be tempted to use other types of solder, such as plumbers' solder which may have different proportions. The type of lead you need is frequently advertised in the motoring magazines or you could get it from specialist motor factors.
I recommend Frost Auto Restoration, who have an ideal starter kit. They can be reached here:- www.frost.co.uk. You can also get lead and lead kits from www.eastwoodco.com
I have used plumber's solder and it seems to work all right, (although the melting point is different) but it is best if you stick to the correct lead.
Quantity
Make sure you order plenty of lead because,
a) You will use more than you expect, even when you get it right, and
b) You will put most of it onto the garage floor as you start to learn the skill!
Tools Required
To lead load you need the following items:
1) Sticks of lead as described above,
2) A flat or shaped wooden paddle to apply the lead,
3) A source of heat such as a plumbers' blowlamp,
4) Flux, or solder paste.
These items will be described as we go on.
Process
The leading process consists of five steps, as follows:-
* Cleaning,
* Tinning,
* Application,
* Shaping and finishing
* Cleaning / removing the flux.
Cleaning
The first job to do is mark out which area is to be loaded. This will depend a lot on the job and the size of the repair. Remove all paint and primer from the area to be filled, plus a little all round as the lead must be blended into the surrounding metal. Use a wire brush or scraper, and if necessary use the blowlamp to burn off the paint. Don't use so much heat that you cause distortion in the panel. If the dent is at the centre of a panel, consider shrinking the metal to remove the dent, as heat applied to the centre of a panel will cause a larger dent to form!
A final rub over with some coarse emery paper will help to get a clean, shiny, rust-free surface.
Tinning
Next, the tinning process. This is the key to working with lead, as the better the tinning process the better the finished job. Once again, use the proper flux for the job, not something borrowed from another trade. Tinning flux contains chemicals which clean the surface being tinned. Apply a little heat to the area being tinned, then apply the liquid flux with a small paint brush.
If you do not have enough heat, the flux will form into little balls and stick to the panel. Too much heat and the flux will shine very brightly and then dry up.
You need to end up with a layer of dull
grey flux ALL OVER the required area. If you wipe it when warm it should shine
bright silver. UPDATE: I'm advised the flux should turn almost black before you wipe it.
When the area to be filled, plus a few inches of the surrounding area, has been tinned, you are ready to apply heat and solder.
If you are adding more lead to an existing lead job, you must go through the tinning process again, unless you can guarantee that you are using the same lead etc. For example if you wanted to "improve" on some-one else's repair you should always re-tin. If you did the repair an hour ago and now find you are not happy with it, you can probably get away with just adding more lead. The rule is, if in doubt - tin!
Application
Using the plumbers' blowlamp, apply a gentle heat to the repair area. A good spread of heat is required, which is one reason that the oxyacetylene torch is not really suitable, since it tends to be a very localised heat source. Heat the steel until it is hot enough to melt the lead stick held against it. This is where the skill comes in, knowing how hot to make the steel.
When the lead is hot enough, twist a small amount off, so that it comes away from the stick of lead. If you have got things under control, you should have a small lump of lead sticking to the metal. Repeat this process until you have several lumps of solder stuck to the tinned area. If in doubt, put too much on!
Now, using the wooden paddle, or a plumbers' moleskin if you can find such a thing (I can't!), heat the lumps of lead gently until it starts to melt and look shiny. When you get the temperature right, apply the paddle (which should be soaked in fresh oil or tallow to stop it sticking to the lead) or the moleskin to the melted lead and spread it out over the tinned area.
Repeat this process until the tinned area is covered with lead. You may find it very difficult to melt two adjacent lots of lead together, and also difficult to add more lead on top of lead already applied. Don't think you can learn this technique in five minutes -- you won't !
Shaping and finishing
Once the lead is applied and cooled, file it with a body file, or scraper, but be sure to wear a protective dust mask, as lead can be a severe danger to health. Don't ever use a power sander or grinder on lead, because the action is too severe and you will find the lead flying off in little pieces. As
well as upsetting your restoration efforts, lead dust is considered to be a major health
hazard.
Another reason for not using a power tool is that you could actually create heat in the lead. This can cause a condition known as "sink" where you are left with a tiny ring round the lead repair that is actually lower than the body panel. This sort of problem will be cured by adding more lead (remember to tin the surrounding area if required) or you could resort to some plastic filler!
Cleaning and Removing Flux
Update: You MUST always wash the completed lead job with clean
water to remove any acid left over from the tinning process. If this is not done, it can "kill" paint which is subsequently applied over the lead repair. Thanks to Terry Burville and several others for pointing this out!
Problems
1) A problem I consistently found was I that I used just too little lead. Err on the side of too much lead rather than too little.
2) Keeping the lead at the correct temperature. Too hot and it will melt completely and drip away. Too cold and it cannot be spread. Beginners to this technique should always start working on a horizontal surface, for working on a vertical surface will just put all your lead on the floor. Leading is a useful technique, but one which needs a lot of practice to get right.
3) You may find you have to fill in little depressions with plastic filler or spot
putty, so don't be discouraged if you find you have to do this. It means you were very close to getting it right. Not everyone can master this skill. Next time, use a little more lead.
Here is a practice door. The top two circles of lead are okay, but the lower, larger one shows signs of not enough lead being applied. You may be able to re-heat this lead and add some extra. This panel is not to be used again, so I could try to recover the lead from the repairs, as described below.
Safety
Make sure you wash your hands thoroughly when finished with the lead. DO NOT eat or drink while working with lead.
If you are in any doubt about your ability to use lead, then don't. Plastic filler if used properly is much easier to use and still gives a professional finish. The secret is putting enough effort into it!
Recovering lead
You know all the lead you dropped onto the floor?
Well, the good news is it is not wasted. Collect it all up, keeping it as clean as possible -- no dust from the garage floor -- and place it into the "V" of a piece of angle iron. Block one end of the angle iron, and place it on a slight incline so that the molten lead will flow towards the blocked end. Now melt the scrap lead with the blow-torch and it should all flow into itself and form a new stick. You can use this stick again. However, I believe there is a limit to how many times you can repeat this process.
Filling-in Small Holes in a Door
If you have a door where there are small holes, perhaps where a mirror was mounted, and you want to fill in the holes - this can easily be done with lead. Clean the area
well with a sander or coarse paper. Now countersink the holes, or dent them very slightly using a ball-pein hammer. You could also hold the ball-pein against the hole and hit that hammer with another hammer. The idea is to create a small depression with the hole at the centre.
The top of this door had three holes where screws had been used to hold a mirror on. It has been countersunk slightly, then tinned, then leaded. The final job was finished with abrasive paper. Finally, two new holes for a new door mirror were drilled.
Now the hole is truly countersunk, tin the area as described above. Now add some lead - enough to fill the hole - remember to err on the side of too much rather than too little. To avoid the lead running through the hole you will need something held beneath the hole that is not "solderable". You can use a file, or a strip of aluminium or stainless-steel. A piece of wood will also do the job. Remember to remove whatever you used when the lead cools. In the words of an expert:- "Easy peasy, ten minute job!"
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Finally, if your flux dries up in the container, the solvent you need is some plain
water. Don't add too much. Just enough to get the dried up flux back into a paste.
There is an excellent lead-loading video on-line for free downloading here:-
http://www.sovereigncoachworks.com/page2/page2.html