Cavity Wax - the Truth, the Whole Truth by Paul Courtenay

Back in 1997 I saw a test in Practical Classics of a number of anti-corrosion cavity wax treatments that claimed to be the ‘best test’. Certainly, the test was quite rigorous, and subjected the treated samples of welded angle iron to all kinds of horrors including the dreaded salt spray. The waxes were tested for their ability to penetrate seams, adhere to the bare metal or rusty surfaces, how much shrinkage they demonstrated during the drying process and finally their ability to ‘self heal’ over scratches in the protective layer. The test was carried out over 500 hours (three weeks to you and me) and the winner was…… Dinitrol 3125, with Plastic Padding and Waxoyl products coming in a close second. So was this the ‘best test’?

Being in a half-German household, and having spent nearly ten years on the continent (we are back there again after 5 years in the UK) I do read the occasional German classic car mag. Well, as if by co-incidence, one such magazine was running a similar test at the same time. However, in a predictably thorough fashion, the German test crew went a few steps further. They constructed twenty box sections with small openings at each end to simulate a car sill. These box sections were mounted on stands out in the open and sprayed internally and externally with salt-water solution on a regular basis after being treated with the various products. The samples being subjected all the time to the real conditions of outdoor life: rain, sunshine, dew and draught.

The initial test I read was conducted after one year, using an endoscope to peer into the box sections periodically and photograph the insides. The test results put the waxes tested by Practical Classics in roughly the same order, but hang on – why was Dinotrol, Waxoyl and the other waxes so far down the list?

The Germans had not only tested the common cavity waxes that we are familiar with in the UK (and which provide advertising income for the UK motoring press), but also two products that are classed as greases, not waxes and which are not easily available in the UK. Mineral wax is normally a paraffin and presumably a grease is somewhat different. Both of these products excelled in all the tests, but were far and away the only products that would ‘creep’ after application. Also being a grease with no solvent, the layer does not shrink as there is no evaporation and of course no smell afterwards (you know the smell of Waxoyl in your car? – that’s the smell of your wax layer drying, hardening and eventually cracking). The clear winner was Michael Sander’s Corrosionsschutzfett! (long word meaning rust prevention grease)

Now, I know this sounds a little beyond belief, but Herr Sander just happens to live in the next village to where we now to live in Schleswig-Holstein, and after a tour of his workshops and a look underneath two examples of customers’ cars which he had treated over ten years ago which were up on the ramps. The cars had both been treated underneath with only paint and his protective grease – it looked dirty for sure, but completely rust free. Without hesitation I sprayed 8kg of his grease into my Lancia Montecarlo in 1997, and another 8kg into my FIAT X1/9 in 2000 – both cars not famous for their anti-corrosion treatment from new. I can report that on both Italian cars I have seen ZERO deterioration in the areas that I treated. One box-section which I unfortunately missed on the Lancia was perforated within two years!

As for the test in ‘Autobild’, after FOUR YEARS of weather and salt spray, the testers showed what was left. Only the box section sprayed with Michael Sander could be removed from its stand without the steel disintegrating into a brown, crumbling mess. There was simply no competition. What more could you ask? I am a convert. And so are about 100 body shops in Germany.

So far it’s all good news, but of course there is a downside. These ‘greases’ are more or less hard at room temperature (with a consistency similar to lard) and need to be sprayed into the cavities at a temperature of at least 90° C. This not only requires special spraying equipment but also some understanding from the good lady as you heat up litres of ‘orrible grease on the hob of the newly fitted kitchen! I bought a purpose made spray pistol, thermometer and a variety of probe nozzles (including a brilliant 360 deg spray for those box sections) for about £100 and some peculiar apparatus made of cardboard tubes and an old hair-drier to pre-heat the nozzles and probes. It was fairly messy, and being hot grease you only have a few minutes per batch before it gets too hard to spray. Although having done it a few times I have plenty of helpful tips now (like, don’t do it on a cold day – it won’t work!)

Incidentally, before the hot spraying I scrubbed the wheel arches and floor clean with warm water and detergent using a variety of brushes or rags and allowed it to dry thoroughly before treating, taking care to clean up all the drain holes beforehand. Tip: always cover the entire floor area with decorator’s plastic sheeting, and tightly cover all brake discs with plastic bags and tape – I spent a lot of time on my hands and knees cleaning the garage floor with white spirit the first time!

However, a vital step before doing this work is to understand HOW the body is constructed and WHERE are the box sections. I am already planning for the later spraying of the 96 (once it is welded and painted) and due to the way the entire SAAB body is put together can only be described as strength itself, there are very few actual box sections compared to many other cars, but notably: