Ensuring that your classic is properly protected against corrosion should be an ongoing process.
Once a year, check the condition of the underseal. If it’s starting to flake away, you need to reapply it. Cavity wax can also start to dry up and crack over time, so this will need repeat applications.
The good news with wax is that, once you’ve sorted out access holes, it’s an easy process. In an ideal world, you’d raise the car on a two- or four-post ramp, using air-fed guns to apply the wax and larger areas of underseal. Not everyone has those luxuries, however.
We sourced an aerosol kit that included rust converter, underseal and cavity wax, and raised the car on small ramps when needed. This gave us enough clearance.
Bear in mind that rust converter will work on surface corrosion only, and the other treatments that are supplied are for prevention rather than cure. It sounds obvious, but if you find any serious rot, you’ll need to deal with it before applying anything over that area.
There will be times when you’re spraying products upwards, so make sure that you protect your eyes by wearing goggles, and it’s also advisable to don gloves and a mask.
STEP 1: RAISE AND SUPPORT
Start with the wheelarches. Raise the car and securely support it on axle stands. Remove the road wheel and cover the hub and braking components – you want to keep the latter free from anything waxy. If you do accidentally get overspray on a disc or caliper, wipe it off using brake cleaner.
STEP 2: OFF WITH THE OLD
Use a wire brush to remove loose underseal or dirt. You need a good surface for the underseal to adhere to, but you don’t need to worry about going back to bare metal. Jet-washing the arches before you start is a good idea, and should leave you with minimal dirt to remove at this stage.
STEP 3: APPLY CONVERTER
If there are any sections with surface rust, make sure you spray them with rust converter before proceeding any further. Where this is needed, you’ll need to wait for it to flash off before starting to apply the underseal. Check whether a converter is part of the kit before buying.
STEP 4: PROTECT THE ARCH
Begin by loading up any seams to guarantee good coverage on those areas, then apply the underseal to the rest of the wheelarch. Ensure that you spray under the lip of the arch. Immediately wipe off any overspray that gets on to external paintwork. Keep shaking the can to achieve the best atomisation.
STEP 5: CREATE ACCESS HOLES
If you don’t have access points in your sills for the application of cavity wax, create your own. The Rustbuster kit comes with a 10mm drill bit and a supply of plugs for this reason. On a medium-sized classic, one hole in the middle of the sill should be enough for the probe to reach either end.
STEP 6: APPLY THE WAX
Insert the extension probe, start spraying the wax, and smoothly withdraw the probe. Repeat this in the other direction. Choose a nozzle that gives fine atomisation and a 360º ‘cloud’ of wax so that you achieve the best coverage. If necessary, dab underseal around the access hole and plug it.
STEP 7: DOORS AND POSTS
You might have to drill access holes in the doors and posts, too. Mask the area with tape and use a centre-punch to mark the exact point you want to drill. This prevents the bit slipping. Fully insert the probe and, again, withdraw it smoothly while spraying. Then plug the hole.
STEP 8: UNDERBODY PROTECTION
The final stage is to coat the floorpans and other major underbody areas. A ramp is obviously ideal for this but, however you gain access, make sure that you have adequate ventilation. Wipe off any excess underseal that finds its way on to the exhaust system.