Shot Blasting
Shot Blasting and Painting
The Importance of Shot Blasting: Protecting Your Boat for the Long Term
What is Mill Scale?
Mill scale is a type of iron oxide that forms on the surface of steel during the hot rolling process. While it may appear as a smooth, bluish-grey coating, it is actually porous, brittle, and poorly adhered. Despite its appearance, mill scale is not a suitable protective barrier – and it can cause serious issues if not properly removed before painting.
Why Must Mill Scale Be Removed?
Although it may seem convenient and less expensive to paint over mill scale, doing so severely compromises the effectiveness and longevity of the paint system. Paint applied over unprepared or inadequately cleaned steel is prone to cracking, delamination, and premature failure. Once the mill scale lifts or “pops off,” it allows moisture to penetrate, triggering a galvanic reaction that leads to pitting corrosion of the underlying steel.
This corrosion can quickly spread beneath the coating, causing further cracking, flaking, and more widespread damage – ultimately shortening the lifespan of the boat’s protective finish and steelwork.
All mill scale must be removed to present a uniform and clean surface.
This shot blasting video has had an impressive 113,000 views. Subscribe today over at https://www.youtube.com/@bluewaterboatbuilder
Our Process
At Bluewater Boats, we remove all mill scale using abrasive shot blasting, preparing the steel to a Sa 2.5 surface profile. This not only ensures a clean, uniform surface free from contaminants, but also creates the ideal profile for paint adhesion – critical to achieving the durability and protection your boat deserves.
At Bluewater Boats, we’ve been shot blasting hulls for over 20 years. Many of our previous builds return to us for re-coating as part of their long term maintenance, and we’re proud to say that we have yet to find any pitting on a hull originally shot blasted by us. This is a testament to the thoroughness and quality of our surface preparation process.
We also carry out restoration work through our sister company, Awlworks Limited, which specialises in shot blasting and applying two-pack epoxy blacking to older hulls. In most cases we encounter boats with significant pitting caused by inadequate preparation or poor quality coatings from when originally built. Where necessary, we also undertake re-plating work to restore structural integrity as well as deep pit welding.
Awlworks offer a choice of comprehensive shot blasting and coating packages to give your boat the highest level of care and long-lasting protection:
Option 1 – Hull Protection
- Shot blasting of hull sides and base plate
- Application of a two-pack epoxy blacking
Option 2 – Full Boat Protection
- Shot blasting of hull sides, base plate, and superstructure
- Application of a two-pack epoxy blacking to the hull
- Application of a two-pack paint system to the superstructure
Both options ensure your boat is fully prepared, protected, and finished to the highest standards — preserving its condition and value for years to come.
Building New or Restoring Old
Whether building new or restoring old, we approach every project with the same commitment to quality and detail – ensuring every hull is properly protected for years to come.
Painting over mill scale may seem like a shortcut – but in reality, it’s a false economy. Proper surface preparation is key to the longevity and performance of your boat’s protective coatings.
With our rigorous attention to detail, you can be confident that every Bluewater boat is built to stand the test of time.
Painting
Two Pack Superstructure Paint Systems and Two Pack Epoxy Blacking
At Bluewater Boats, we are proud to be leading the way in professional shot blasting for boat hulls. With over two decades of experience, our shot blasting process is not just a step in the build - it's a critical foundation for the long term protection and performance of your boat. We don’t cut corners. Every hull we build is shot blasted to the industry leading Sa 2.5 standard, ensuring the surface is perfectly prepared for the application of high performance coatings. This meticulous preparation is what sets us apart from others. In fact, we’re yet to see pitting on any of our own shot blasted hulls - even years after launch. That level of durability speaks volumes. Following this process, we apply a premium two pack epoxy blacking system, as well as a full two pack multi stage coating system for all external areas of the boat.
Hull Protection – Below the Waterline
After shot blasting, we apply Jotun Jotamastic 90 — a high-performance, two-pack epoxy blacking — to the hull up to the top rubbing strake. The base plate is excluded as standard, although we can also shot blast and apply the same two-pack epoxy blacking to the base plate if required. This system provides outstanding durability and long-lasting protection, helping to safeguard your boat against corrosion and wear for many seasons ahead.
Why Jotun Jotamastic 90?
- Exceptional durability in both atmospheric and immersed environments
- Surface-tolerant, high solids, and abrasion-resistant
- Provides excellent corrosion protection in both salt and fresh water
- Harder-wearing than conventional blacking products
- If scratched, the blast profile prevents the damage from spreading
- Note: When exposed to direct sunlight, chalking may occur—this is normal and cosmetic only
Superstructure – Above the Waterline
We follow a multi stage, professional two pack paint system to ensure longevity, protection, and a superior finish:
- Shot blasting to Sa 2.5
- Two pack high build epoxy primer
- Two pack epoxy finishing primer
- Non-slip coatings on gunnels, bow deck and stern deck
- Two pack acrylic topcoats – including metallic colour options
Topside Finish – Alexseal Acrylic Topcoat X
For a premium finish above the waterline, we use Alexseal Acrylic Topcoat X, a high-gloss, two-pack acrylic system developed for the yachting industry.
Benefits of Alexseal Topcoat X:
- Combines acrylic and polyester technology for exceptional gloss and depth
- Easily sanded and polished for future maintenance
- Excellent UV resistance, colour stability, and abrasion resistance
- Withstands saltwater exposure and fuel contact
Why Choose a Shot Blasted & Two-Pack Paint System?
- Superior adhesion and corrosion resistance
- Increased lifespan compared to traditional paint systems
- Lower maintenance over time
- Professional grade finishes both above and below the waterline
Bluewater Boats are committed to protecting your investment with industry leading materials and processes. Whether you’re commissioning a new build or looking to restore and repaint your boat, our team ensures the highest standards every step of the way.