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Technology, old cars, & other stuff...


Saturday 28 January

Rust Preventative Coatings

A few years back, I had some anti-rust coatings left over from various projects so I decided to try an experiment into their effectiveness. I simply applied the coatings to some scrap steel and nailed the samples to a fence post and left them there, checking every now and again for detrioration and taking some photos. The samples were exposed to wind, sun, rain, sleet, snow but were never immersed.

The samples were made with some scrap steel from old TR7 panels. I ground away some of the original paint & primer ready for the coating but left some of the original 30+ year old British Leyland paint finish intact - interesting to compare how this performs to the coatings under test.


The coatings I had available were as follows:

Category Product
Cavity Wax

Dinitrol 4941

Rustbusters MIL-SPEC


Rustin's Water-Based Anti-Rust Paint

Hammerite Smooth

Aldi's Metal Paint


Tetrosyl Tetro Schutz

Dinitrol 3125


Rustbusters Phos-Kleen B

Taylor McClure SCALE-X 42% Phosphoric Acid

The treatments are phosphoric acid based solutions that are mainly used to remove rust, clean and prepare the metal for paint but can have some long-term rust prevention properties. Phosphoric acid based products are not a complete rust prevention solution on their own but I included these just to check the extent of any rust inhibitor properties. And in fairness to the cavity waxes, I'd guess they're not designed to be exposed, so this test is probably not representative of their performance in their intended environment. However, this does seem to be a fair test of underseals and paints.

Here's  the result after 7 years:

 September 2013 (3 months since start)  July 2020 (85 months since start)
2013 2020 
2013  2020
 2013  2020


After 3 months, all of the bare metal samples had rusted over and, as expected, the rust penetrated deeper as the years passed. The samples coated with Phos Kleen B seemed to take longer for rust to develop.

Of the paints, the Aldi Metal Paint seems to have deteriorated more than either Hammerite Smooth and Rustin's Water Based paints - but note that the Aldi paint is around half the price of Hammerite. Rustin's appears to be the most sound.

All of the cavity waxes seem to have deteriorated badly after 7 years - but as noted above, this may be an unrepresentative test as they are not normally exposed to all the elements. But it's worrying nevertheless.

Of the underseals, Dinitrol 3125 seems to have broken down badly in a very similar way as Dinitrol 4941. Pretty shocked by this. Tetrosyl Tetroschutz, on the other hand, still seems sound.


The next step is to clean off all the coatings and have a look at the metal underneath. Watch this space!



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