If there is one thing that’s feared, loathed and hated by car people more than Federal regulations, insurance company rules and premiums and even fuel costs, it’s rust. Rust has destroyed more classic muscle cars than anything else out there. Sure collisions have claimed their share but rust doesn’t require poor driving to take out a valuable muscle car. Just a little air and water and a bit of time is all that’s needed. No action on the owner’s part is required. Rust happens all by itself.

Sure there are some things that can be done to limit it and automakers have for decades made efforts to combat the problem, some more effective than others, but none have completely succeeded at stopping it.

So, automotive rust repair has been around almost as long as there have been cars.  And muscle car restorations have been a thing since these highly desirable models have needed extensive repairs because of it.

The benefit of a professional restoration over simple rust repair is that during a restoration the car is typically stripped down to bare metal and every rust damaged part of the car is either repaired or replaced. Also, more time it spent sealing everything against water intrusion to keep that part of the rust equation out of the picture.

One of the areas that are given extra attention are the sheet metal seams; that is anywhere two pieces of sheet metal are joined together, usually with spot welds. Moisture loves to get in between two pieces of metal where it can sit for longer periods of time before it evaporates giving the oxidation process more time to get started.

Muscle Car Restorations has long given extra attention to properly sealing all the seams on their projects but recently they have taken the process to a new level with the introduction of a weld through seam sealer product from 3M. This urethane product is designed to be applied between the two pieces of sheet metal instead of just being applied over the top of the seam. The product also allows the parts to be spot welded together to duplicate the factory assembly process. The obvious benefit is that the seam is sealed from the inside so that there is literally no place for any moisture to go to collect between the parts.

Does this spell the end of rust in muscle cars? It would seem that is very likely the case.

This Camaro is getting a custom firewall. This is the final mock up ready to be welded in place.
In this case there are three layers involved, the upper cowl, lower cowl and the new custom firewall. This will be a great test of the new sealer as the welds will have to join three layers instead of the usual two.
The gold in between the panels seen here is a coat of Copperweld Weld-Through Primer. This is standard practice at MCR. Any place two pieces of metal are joined into a seam, this coating is applied between them to prevent rust. Copperweld is a rust preventative that, as the name implies, can be welded though.
A strip of masking tape is placed above the seam to keep any excess sealer off of the cowl. This will of course make the final clean up easier.
The Sealer is a 3M product – Urethane Seam Sealer black, item number 08367. It is approved for bare metal sealing applications.
The sealer is generously applied between the parts. The masking tape will keep any excess off of the cowl.
As there are three panels involved, a second application of the sealer is needed to seal both seams.
After tweaking the spot welder adjustments a little and some successful test welds, the first welds are applied to join all three panels.
As the welds continue, the sealer is squeezed out indicating that the panels are being tightly joined together. The sealer is performing as advertised and is not interfering with producing good quality spot welds.
A variety of welder arm lengths are needed to reach all the areas.
With the welding complete, the excess can be wiped off leaving behind a clean seam.
The welds are tight and the finished seam looks great. The sealer has about a five to ten minute working time and can be painted in 30-45 minutes or so. It is permanently flexible so it won’t shrink or crack over time. The usual seam sealers can be applied over this if the factory look is desired.