It bears repeating: steel is today’s bargain boatbuilding material. If possible, you should choose pre-shot blasted and primed materials. The terms sandblasting, grit blasting, and shot blasting have similar meanings. The process for all three involves blasting the steel plate and bar stock with a grit to remove the impurities from the surface and preparing the material to receive the prime coating (see Chapter 9, Grit blasting and Priming). If you’re building outdoors, you’ll lose some of the percolating. But the benefits of pre-prime-coating are so positive that it’s worth your consideration. Pre-primed steel not only provides a cleaner working environment, but it will encourage you to arrange a temporary cover. When you’re welding prime-coated steel, you should wear a protective mask to avoid inhaling the fumes released as the prime coating is burned off around the weld. If you use a kit that is coated with Sigmaweld MC primer, there are very few fumes; it is always advisable to wear a protective mask and other protective gear when building any boat.

   One of the main benefits of using shot blasted and primed materials is that when you have completed the hull and deck, you should not need to shot blast or grit blast the interior. This part of the blasting process is the most time consuming and expensive. If you can avoid it by using primed, painted steel, it’s worth the cost and effort of obtaining this material and keeping your project under cover. You may wish to consider using self-applied shot blasting and priming your metal before you start construction. Make sure you use weld primer that is specially formulated for use on the plate to be welded. One brand is Sigmaweld MC primer; other manufacturers should have similar products.

    We used to think that building outdoors and using unprepared steel was a good idea; the theory was that the weather removed some of the mill scale and other surface impurities. But, as you will have gathered, we’ve changed our mind. It may take longer than originally planned to build a boat with unprepared steel, and the wastage of metal through rusting could be a sizable factor in its life expectancy. Our advice: NEVER allow your boat to get rusty during construction.