Some of you may remember my ordeal with the floor on my 240d last summer.

After welding the new plates in and applying seam sealer, I painted it with Miracle Paint, a rust preventative coating similar to POR-15, but better. Then I did what everybody warned me against and used a spray undercoating.

"Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so."

  • -Douglas Adams

Now I'm pretty diligent with keeping my car clean through the winter, using a touchless car wash that also sprays the undercarriage. Well, after what was hopefully the last winter wash I decided to take a look underneath and see how my repairs were holding up.


  • "Lets just take a gander here.....




  • the next few days.


Now my potential solution. I've used this product before when installing my wheel well liner 2 years ago, and noticed that it has not been affected in the slightest by road salt. I contacted the company and they informed me they have a brush grade version sold as a roof repair/sealant called "Through the Roof", though they wouldn't say if it would withstand my proposed application. So I am performing an experiment to test both Through the Roof's and Miracle Paint's resistance to rust.

As visible in the lead picture I have three test pieces.

  1. small piece of untreated steel
  2. small piece coated in Miracle Paint
  3. larger piece, half of which is coated in MP, then about two thirds covered in Through the Roof, with the bottom third exposed steel


I have them in a small tub and will be applying a water and rock salt mixture every few days. I'll do updates periodically, and if anyone has suggestions of any kind please let me know.