Sunday, September 5, 2010

Use and abuse of body filler

Whilst the appearance of panels which will ultimately be hidden underneath carpets or undersea! is not important, it is obviously vital that external panels arc not only strongly fitted but also that they look good. Unfortunately, some of the operations during a restoration create welded seams which will show up through paintwork and which consequently need to be hidden before painting. Shallow dents in external panels, which can easily be accidentallycaused during the mechanical build-up, also have to be hidden. The materials for achieving a smooth surface and the correct lines in such cases are either bodyfiller or lead (or a combination of these).
Many classic enthusiasts abhor bodyfiller despite the fact that, if properly used, this material can give perfectly acceptable results. Unfortunately;bodytiller has suffered from a 'bad press' because the number of cases of filler misuse easily outnumber cases of proper use.
Bodyfiller is intended and perfectly acceptable for tilling shallow dents in external and non-structural car body panels. It is not intended to be used to bridge holes, nor to fill deep dents or cover up areas of hodyrot. Yet those looking for a car (even '70s cars) like the Beetle will doubtless encounter many examples in which quite large holes and deep dents have been filled with a lump of bodyfiller or a mixture of GRP and bodyfiller.
Bodyfiller should only be used to obtain a smooth surface on meta] which has shallow dents, such as might result from heat distortion during welding operations, from minor parking bumps, or on a seam produced following the fitting of a repair part-panel. Deep dents should be beaten out so that a minimum of filler is needed. Bodyfiller is the modern equivalent of lead, because bodyshops and car manufacturers for many years treated small undulations in external car body panels by firstly painting on a lead 'paint', melting this to 'tin' (coat) the area in question and to form a strongly-bonded layer to which the lead could adhere, then melting on and spreading with a spatula further lead to build up to the required height. This process is known as 'lead loading' or 'body soldering'. Bodyfiller is far easier to use than near-molten lead, as well as being inherently safer! Lead loading kits and associated equipment are available and widely advertised.
Lead loading offers one great advantage over body-filler because the lead actually seals the surface over which it is applied, and in doing so it prevents future rusting (as long as the metal underneath is bright when coated with lead). In the author's experience, many professional restorers use lead loading for this reason, although obtaining a final smooth finish with lead is not easy, and you could use a very thin layer of bodyfiller on top of the lead to obtain the best of both worlds!
A combination of lead loading and the use of body-filler is especially useful when dealing with welded seams. Clean then de-grease all the area in question (the metal must be perfectly clean), then paint on solder paint, which is obtainable from companies such as Frost Auto Restoration Techniques (address at the back of the book). Apply heat to the solder paint until it melts and wipe it so that it coats the metal, then wipe away any flux from the surface using a damp rag. The metal is now sealed, and may be built up using either lead or bodyfiller.
It must be pointed out that lead is highly toxic, so if you do4lecide to work with it, treat it with the caution you would if dealing with any other toxic chemical. Don't attack a leaded joint with apower sander, because this will fill the air with lead particles which you will breathe alwaysuse body file to profile lead, andwear a fine dust mask.

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