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Welcome to Bluewater Boats Ltd

Shot Blasting

When you purchase a Bluewater Boats hull we offer our shot blasting service, unlike many other hull builders.

Shot blasting removes the mill scale.  Mill scale is a type of iron oxide that is formed on the surface of the steel during the hot rolling process and is porous.  The very high surface temperature combined with high roller pressures result in a smooth, bluish grey surface.  If mill scale were a uniformly well-adhered covering to the steel section, then it would make an ideal protective barrier.  Unfortunately, mill scale is not uniform, nor is it well-adhered. 

This latter item is of concern in that many projects have had high quality, expensive protective coatings applied directly over mill scale and inadequately prepared steel only to have the entire structure and coating system fail within a very short period of time.

The mill scale is fact looks like a scale and it can “pop off” the surface, cracking the coating and allowing moisture to penetrate.  This allows a galvanic reaction to occur which results in pitting corrosion (rust) to the base steel.  This will result in a growth of the corrosion under the scale and produce further cracking to the coating and expose greater areas and thus more corrosion. 

All mill scale must be removed to present a uniform and clean surface.

At Bluewater Boats our steel surfaces are cleaned with to a SA 2.5 profile with an abrasive blast.  This will remove the mill scale and provide a surface profile that will give the paint system its design requirements.

Painting over mill scale, however tempting, is a futile exercise, as the presence of mill scale on the steel surface accelerates the corrosion of the underlying steel.