"Cavity Wax Injection 911/912
Introduction and Principle.
When applying cavity wax it needs to be kept in mind that the car’s metal needs protecting in the following areas:
Anywhere that has been welded. ‘Weld Thru’ primers burn off directly around each weld pool, and despite claims to the contrary ‘E’ Coat type finishes do not completely penetrate welded seams. Both scenarios leave the metal bare, and in the case of welded joints, often acidic compounds are formed during the welding.
Any area that is known to rust on your particular model of car: even if your example has not yet rusted there. These include ‘mystery’ rust areas that are often as a result of the internal structure trapping condensation causing rust that is hard to explain just looking at the problem externally.
All lower cavities however difficult to reach.
Equipment, Materials and Method.
Whilst cavity wax is available in aerosol form, these are best regarded as a ‘back up’ to the main waxing process. These tend to have very good penetration, however, so are excellent in areas that the main wax cannot reach.
The main waxing ideally should be carried out with a compressor and air fed gun. These can come as an accessory for a ‘Shultz’ type gun. These are cheap enough, but the lance provided tends to be rather large (8-10mm diameter) and not very long (450-600mm). However they do enable a good coverage of the car’s internals if they can be reached, as the wax can be injected at very high pressure, and so can be flung some distance. These require at least one ‘Shultz’ type canister, ideally of wax, or at a push a cleaned out underseal canister to load the wax into.
The absolute ideal is a dedicated cavity wax gun. These come with a variety of flexible and solid lances of various lengths, some of the flexible lances reaching several feet. Perfect for the job, although require filling often.
There are a number of cavity waxes sold; Waxoyl and Dinitrol are probably the best known in the U.K. although Wurth and many car paint factors will have other brands. These have not been tested, but it is probably safe to say that any brand of wax is far better than no wax at all. Waxoyl at least is available in 5L cans, and the 911/912 will use at least this, with 10L being possible, perhaps with a small reserve left over.
Both of the air-fed methods are more successful if the wax is well pre-heated. I use a single ring electric cooking hob (£14) left on it’s lowest setting (you can almost hold your hand on this hob at this setting). The lid of the wax drum is left off, and the can sat on the ‘warm’ plate. A health and safety friendly alternative is to stand the wax in very, very hot water. The water will need to be changed often though, as ideally the wax needs to have melted to an engine oil-like consistency. It’s worth shaking the can regularly to assist the warming process (lid on!).
Finally, when using high pressure injection, the wax produces a lot of vapour: it is essential to use a good quality breathing protection whilst using the wax. When the process is finished, the mask will be found to have a thin sticky layer of wax over it: much better than rust-free lungs. It may also be worth covering the external paint/glass of the car for the same reason. Whilst the wax may protect the paint, it is a little tedious to remove, and it encourages small particles to stick, risking scratching upon removal.
If the car is in use, it may be beneficial to have the underside steam cleaned, or at least pressure washed before starting work, especially should underside treatment be desired. It is also important to make sure the car is well dried before starting. This means the ideal time for this work is during the summer, but in the real world try to garage the car for a while before treatment, ideally with a de-humidifier running.
Areas for Waxing: 911/912:
This list is not exhaustive: it was arrived at by past experience of waxing, coupled with areas that have required rust repairs on a number of cars. Many of the points will require holes to be drilled, and then plugged with grommets after treatment. Remember to paint the raw edges of fresh holes. They are best drilled with a stepped drill or dedicated sheet metal drill. A conventionally ground twist drill tends to snatch, distorting the metal and leaving a less than round hole"
