Most cars used in wet or snowy areas have some kind of under body treatment in the form of Tectyl, Mercasol or similar that they got when they were new. If used on salted roads they are very prone to rust. Tectyl on a new, spotless car works well for many years. But eventually it dries out and rust creeps underneath, especially along seams and joints. Applying new Tectyl will not help. You can remove old Tectyl and sandblast, but will still have areas where you don’t reach with sandblasting, such as in seams.
On old cars it is better to use a non hardening product. Various types of oil have been used for many years, and recently lanolin, Fluid Film (FF) has become popular.
I have used FF on my 1994 Land Cruiser 80 since 2010, and thus have pretty long experience with the product.
The car was Tectyl treated when I took it over, and had very little rust. But the Tectyl was starting to get pretty stiff so something had to be done. So I googled a bit and found several tests of FF on German websites. Not so common in Norway then. In this test FF was voted fifth best for cavity treatment after a five-year test, but as the best product for do-it-yourself treatment as it does not require special equipment. Mike Sanders Grease came as number two and can also be used so do-it-yourself, but is much harder to work with since it must be heated to 120 degrees, and was not to be found in Norway at the time
Test (German only): oldtimer-markt.de/rostschutztest
To paint and rust protect read here: Painting and rust protection
Read about welding here: Welding sheet metal
My experience with FF
FF is available in several types. NAS is the most widely used. It is like ketchup in consistency and penetrates and creeps up to 15 cm. That is, it creeps in between rusty joints. It can be used everywhere on the car, but is rather easily worn off by water splash. NAS is easy to work with when you have the right gun. If it is cold then warm the syringe in warm water. Since the NAS is quite thick in consistency, a high-pressure gun is needed. The one I use has a loose handle for general spraying, and a 6mm wand that is nice to use inside the frame. See film below.
Fluid Film Gel BN is like regular fat in consistency. The advantage of it is that it does not wear away so quickly, so it is nice to use in exposed places such as wheelhouses and canals. I use a spreader to apply and then a broom to distribute outwards.
Fluid Film Liquid AR is a new product with consistency somewhere in between NAS and Gel BN. It can be sprayed or brushed on. I have not tried it yet, but should be fine to use in places exposed to splashing.
I think the combination of Tectyl and NAS seems to work well. NAS softens the Tectyl and it creeps into cracks. The NAS wears away relatively quickly, but the Tectyl will protect it. Tectyl also provides better protection against stone chips.
But. after about 5 years, the Tectyl became so soft that it falls off in places when I high pressure wash the car. There I now use Gel BN first. It must be applied before spraying with NAS, otherwise it will not sit.
Alternatively, you can re-apply Tectyl in these places to get better protection against stone chips.
I treat the under-body in the autumn every year. A high pressure wash first is an advantage, but not absolutely necessary if the car is not very dirty. It is more important to wash in the spring to get rid of salt. But it is an advantage that the car is dry, even if the NAS displaces water. I flush the inside of the frame every three years with a crawler nozzle, but spray with NAS every year.
Cavities, i.e. ducts, wheel arches, posts, doors I spray every four years. But NB!, one thing you have to be careful with is rubber. It swells on contact with the NAS.
The picture shows the door gasket on an LC 80 after 7 years of using the NAS. The problem is that the gasket is attached with clips to the door, and through the holes the NAS creeps into the gasket. It will be expensive in the long run to replace gaskets. On cars with glued gaskets this should not be a problem.
Instead, I use Gel BN at the bottom of the doors. It is possible Liquid AR is even better for this use. Fortunately, it does not look like FF affects the hard rubber in the bushings.
Right after treatment, the car smells strongly of sheep, but it goes away quickly. It may also drip a little for a while. On very hot days, it may start to drip and run again. You can easily see how well FF crawls on a dirty car when it creeps upwards from the chassis. But it is easy to wash off with soap or degreaser.
Status after 10 years is:
No new rust. Old rust does not develop further. FF prevents oxygen supply and then it can not rust. It is not the case that if you have any rust then it will “grow” further. Rust must have air.
Disclaimer
Inditravel.org is not commercial and the only reason I mention product names here is because I have personal experience with them
