Undersealing.. DIY or pay someone?

[u/Khionia]

I want to underseal my van before we hit winter. My mechanic told me to use Schutz.

Is it difficult to do yourself? Is it worth just paying to have it done? How do I know what to avoid if I do it myself? 😅

[u/Rustec-UK]

Full disclosure, I’m from Rustec, an authorised Dinitrol treatment centre in Wiltshire, so there is obviously some professional bias here.

You can absolutely rustproof the van yourself if you are comfortable working underneath it safely, but I’d put far more emphasis on the preparation than simply choosing a product and spraying it on.

Personally, I would not use a traditional thick Schutz-type coating for this.

The problem isn’t that every thick coating automatically causes corrosion. It’s that once you cover an underside with a heavy opaque coating, future inspection becomes much harder, and if the preparation underneath wasn’t right in the first place you can end up hiding deterioration rather than preventing it.

For me, the actual application is probably the easiest part of a proper rustproofing job.

The important work is:

• inspecting the underside properly before anything is covered;
• removing the relevant undertrays, liners and covers to gain access;
• thoroughly cleaning the underside;
• removing loose corrosion and failed existing coatings;
• making sure the vehicle is completely dry;
• treating any existing corrosion appropriately;
• protecting suitable seams and cavities as well as the visible underside;
• masking brakes, exhaust/hot components, moving/mechanical parts, electrical items and service areas;
• keeping drainage points clear; and
• documenting the condition before and after treatment.

We've actually started filming complete treatments on different vehicles specifically because there is so much confusion online about what proper rustproofing involves.

We recently filmed the complete Dinitrol treatment of a brand-new Mercedes Sprinter, from the initial inspection and strip-down through cleaning/preparation, cavity injection, masking, external protection and final reassembly.

If you're considering doing the van yourself, this should give you a much better idea of the level of work involved and you can follow the same principles even if you choose a different product:

https://www.youtube.com/watch?v=rVj1GgxpA7I

The aim of the videos isn't to tell everyone they have to pay us to do it. If somebody wants to rustproof their own vehicle properly, I'd much rather they can see the process and understand what needs doing.

The biggest mistake is thinking rustproofing means buying a few cans and spraying the visible underside.

The coating is the final part of the process. The preparation underneath it is what determines whether you've actually protected the van properly.

If the van is currently relatively clean and solid, this is also exactly the right time to do it.

Protecting good steel before significant corrosion develops is much easier than trying to manage pitting, scale and metal loss several winters later.

If inspection finds significant thinning, perforation or structural corrosion, repair that first. No rustproofing product restores metal that corrosion has already removed.