Full Underbody Rust Protection Guide [Seam Sealer, Underseal & Cavity Wax by Dinitrol] BMW E30 | 035

Full Underbody Rust Protection Guide [Seam Sealer, Underseal & Cavity Wax by Dinitrol] BMW E30 | 035

In this BMW E30 build update I do the messy job of applying seam sealer, Dinitrol underseal coating, and cavity wax to the underside of the car, around the floor pans, wheels wells and engine bay. If you're specifically looking for a detailed guide, I did a previous video which was a more in-depth review on the Dinitrol 447 and ML products when I tended to the rear end which you can find here:    • Dinitrol 447 Underseal & ML3125 Cavit...  

Here's what I used in this video:
Ranal Brushable Seam Sealer 1kg: https://ebay.us/Cget4u
Mipa PU 400 Seam Sealer Cartridge: https://ebay.us/62SVeH
Dinitrol 447 Grey Underseal x4: https://ebay.us/FNUGrh
Dinitrol ML 3125 Cavity Wax Brown: https://ebay.us/EHM15O
150L Compressor: https://ebay.us/xxiVq8
Schutz Gun with Cavity Nozzle: https://ebay.us/LWUZej
Troton Epoxy Primer: https://ebay.us/3M7Kuu

I was hoping to bring forward most of what I'd learned about undersealing cars from my previous experience forward and have an effortless time getting a perfect result. Alas it was just as challenging as last time, but again I learned a lot.

To begin with, I'd got the underside chassis of the car in grey etch primer to prevent flash rusting, especially on the areas I'd taken down to bare metal.

With that thoroughly dry, I applied seam sealer to all the areas that needed it such as seams and areas I'd welded patches in. To do this I started with a can of Ranal Brushable Seam Sealer, the same stuff I'd used on the rear. To be honest, when I purchased this seam sealer I did it because it was the best value brushable and over-paintable seamsealer I could find. But it turned out to be an excellent product I could wholeheartedly recommend. I've used the whole can up now.

When I'd tried on the rear end of the car with a brush I had some frustrations getting the finish to look like a high standard, but this time I used an old card, like a credit card, to apply it almost like a filler. I took a chunk of seam sealer on the card and pressed it into the seam, then smoothed it off. This technique is unorthodox, and I haven't seen it used with seam seal before, but it worked so well I think this will be my default method going forward.

From there I loaded the Mipa PU 400 seam sealer into my caulking gun and applied it to the more intricate areas which required seam sealer to be pumped in deeper. The trick with this one is to allow it 5 minutes to firm up, then smooth it off with a rubber-gloved finger. The Mipa PU 400 was also a pleasure to work with in this way.

Seam sealer can take a long time to properly set, and I'd recommend allowing it to completely dry before applying any top coats to it. I gave mine a few days to completely gas out and dry before I then returned to spray on some durable Troton Epoxy Primer on top of these areas and any areas which were to be masked and not sprayed with underseal. I then allowed this a couple more days to dry.

It was time to get the Dinitrol 447 underseal applied to the car, but first I needed to mask all of the studs and mounting faces, plus the fuel tank and rear end of the car to prevent spoiling the nice paint job I'd done on those previously. I did this with a combination of masking take and masking paper.

With the but 150L compressor charged up to 10bar, I dialled down the output pressure to around 3.5bar for spraying and mounted the first can on under seal on the schutz gun. I then climbed under the car and started spraying undercoat all over the place. I'd learned last time that it comes out very fast and can cause a run if you hold the gun too close, or spray for too long. I also learned that the schutz gun can block up very quickly, in particular between cans of Dinitrol 447. Both lessons did not prevent me repeating the issues.

Going forward I will definitely purchase an additional schutz gun or two, and then hot-swap them rather than getting frustrated and wasting time and products trying to clear the gun back out.

I gave it a week and returned to spray in the Dinitrol ML cavity wax using the cavity extension tube on the schutz gun. All in all the results were excellent and I'm extremely confident in the underside of the car in terms of corrosion protection and its ability to resist rust going forward. As this BMW E30 is likely to be a summer toy going forward, I suspect this is a permanent rust prevention.

For more helpful how-to guides and restorations: https://www.spannerrash.com/

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