4 min read

Substrate Repair Differences

Written by
Kirk Carlisle
Published on
November 14, 2022

If you manage any type of collision repair operation, then there is no doubt you have a collection of hats you have to wear each day.

Manager, trainer, customer service; most days, you will wear several of them.  How about a metallurgist?  That is probably one that you never considered needing, but there are several good reasons for understanding this discipline and how it relates to collision repair.

Ten years ago, most panels on a vehicle were mild steel and served no true structural purpose.

The Insurance Institute for Highway Safety stated, “Previous IIHS testing in 1987 and again in 2000 illustrated that cosmetic parts have no influence on crashworthiness, so their origin is irrelevant.”  Just to clarify, by cosmetic parts, they are referring to quarters, roofs, hoods, etc.

Technician using a shrinking hammer on a vehicle repair.

So when it comes to exterior panel repair, does the substrate matter?

Absolutely.  Most manufacturers now consider many of the exterior panels to be structural.  At a minimum, these panels interact with the structure beneath them. So what are some of the more common panel substrates?  The MOTOR Guide to Estimating has a fantastic reference to get you started, but we will look at some common substrates you will encounter.  Most importantly, before beginning any repair, always refer to the manufacturer’s guidelines for substrate and panel repair.

Shiny new aluminum car frame and panels only.


We’ve seen aluminum in shops for years, but what is new is how common it has become.  Unlike many other substrates, aluminum has no memory.  One does not simply ‘pop a dent’ out of aluminum.  Typically the repair process involves heating the repair area to prevent the panel from cracking, but heat limits must be observed to prevent annealing.  If the heat tolerance of the panel is exceeded, it must be replaced.

Stacked unfinished sheets of high-strength steel in a warehouse.

High-strength Steel

High-strength steel is becoming more commonly used, especially in door panels.  As the name indicates, this substrate is stronger than the mild steels used in the past.  This higher strength complicates the repair as the damage is prone to displacing or ‘walking’ during the repair process.  High-strength steels are also more prone to tearing.

Ultra-High-Strength Steel

Traditionally, ultra-high-strength steels were reserved for inner structure components.  However, with decreasing vehicle weight being a major goal in current-generation vehicles, this substrate is now making its way to the outside of the vehicle.  Like high-strength steel, damage to these components will displace during repair, and the substrate is prone to tearing.  Furthermore, many manufacturers do not allow repairs to ultra-high strength steel panels.

Small pile of magnesium shavings.

Magnesium & Boron Steel

While not used on exterior panels, magnesium and boron steel are worth mentioning.  These substrates are listed as replace only.  Magnesium is very hard and prone to microfractures that compromise its strength if damaged.  It is also flammable and requires a type D extinguisher to put out.  Boron steel is exceptionally strong and should not be repaired due to the high heat used in its formation.

What do these different substrates mean to your operation?  

They influence liability and repair profitability.  Not only do we have to correctly identify the substrate and then repair it with appropriate methods, but we also have to document it.  Our repairs are called into question whenever a vehicle we touch is involved in another collision.  Documentation protects you, your techs, your shop, and your customer.

The other big factor is repair profitability.  If you are accepting the same three hours of repair time on every substrate, then your repair costs you money.  There is nothing wrong with getting paid appropriately for your work, and you do more work on a high-strength steel panel than on a mild steel panel.  So how can you both help document your repair and be paid accordingly?  Certainly, manufacturer procedure pages help, but they can be lengthy and complicated.

How can I be fairly compensated for repairing these more challenging materials?

iPhone screenshots of the app in action.

This is where the Damage Appraisal App can help.  With precise damage measurement, substrate-based repair time calculation, and professional reporting tools, you can quickly and easily document a damaged area. Reports highlight the damage with a 3D depth map and suggest a repair time, based on the damaged area and provided substrate information.

You’re the metallurgist, you know what the repair needs.  Make sure you are documenting it and getting paid appropriately for it.  You can get started and schedule your live demo today at

Schedule Your Demo

1.  Insurance Institute for Highway Safety. “OEM vs. aftermarket parts and Honda Fit crash tests”. 15 Feb. 2018,

2.  CCC One. “MOTOR Guide to Estimating”. 2020-2021 Current CCC/MOTORS GTE Guides,

No spam. Just the latest releases and tips, interesting articles, and exclusive interviews in your inbox.
Read about our privacy policy.
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.
Share this post
Just click on the links below to share this post with your friends and colleagues.

Ready to learn more?

Click the button below to schedule a 1-on-1 demo with a member of our team.

Start your 10-Day free trial

Get started for free and cancel anytime, but we don't think you'll want to!