I have just finished a large rust repair/proofing job on my 240D that included surface rust treatment and cutting out and welding of patches where the rust had gone through. During the job I used rust bullet, POR-15, Waxoyl, and Spray-Galv.

Most of the rust proofing was dome with POR-15. It sticks to skin quite well so be careful. I found the POR-15 application very time consuming with the cleaning with marine clean, etching with metal ready, rinsing of metal-ready, drying and applying 3 coats of POR-15 with 3 hours between coats. Although you are supposed to be able to paint directly over rust I still wire brushed the areas before applying it. Even with all the prep-work and following the instructions to a “t” I still had some problems with pealing and non-coating of some areas. The stuff will go on nicely, but while it is drying it seems to tend to thin out in some areas leaving holes in the coat, which is why several coats are needed.

I just used a tiny amount of rust bullet, so I don’t have too many comments about it.

Some of the welding work was in the passenger compartment side of the rocker panels. The rockers are coated with an anti-corrosive coating and waxy coating from the factory. To prevent contamination of the welds I removed these coatings in the area of the repair prior to welding. On the inside of my rocker patch and in any areas with overlapping metal I used spray-galv to as a rust treatment. It is also sometimes called weld-through primer, however I would not apply it within ¼” or so of the weld bead area. It is 90-something % ultra-fine zinc powder with a bonding agent and is supposed to equal hot-dipped galvanizing in rust prevention and can withstand a good amount of heat. I then sprayed Waxoyl into the rocker panels to replace the factory wax coating.

Out of all the products I used, the spray-galv seems to be the best if it works as well as it claims. I am doing some tests with both it and the POR-15 to see how they stand up over time.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine