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COATINGSPRO SURFACEPREP 2015 13 Concrete and Steel dependent on the t y pe of sur face to be prepared, as well as the t y pe of coating system to be insta lled. (T hinner coatings may only require something such as acid etching, but thicker, high-build systems t y pica lly need ag gres- sive mechanica l methods to achieve proper adhesion). "Regard less of the method selected or the tools employed, the substrate must prov ide a sur face that w ill accept the coating system to be applied and a llow for a secure mechan- ica l bond," said Rupnick i of Shot Blast Inc. Jason Stanczyk of Equipment Development Co. (EDCO) agrees. "W hile some coatings and substrates only require a clean surface for adhesion, most applications require mechan- ical surface preparation, which opens, levels, textures, and/or cleans the surface to be coated," said Stanczyk. Another surface prep issue that contractors may encoun- ter on concrete is laitance. In the concrete curing process (hydration) water migrates to the surface and carries sand and cement with it. W hen the water evaporates a weak layer of this sand and cement, known as laitance, is left on the surface. Tis layer is not stable and should be removed before coatings are applied. Laitance can be removed by acid etching, abrasive blasting (nozzle or centrifugal), water jetting, and using mechanical methods, such as scarifers or grinders. If the laitance is not removed the surface tension created by coatings, especially those that cross link, will cause the laitance to release, taking the coatings of with it. Tools of the Trade: Shot Blasters, Grinders, Scarifiers So what exactly are shot blasters, grinders, and scarifers, and how do they difer? According to Paul Robb of Blast Pro, shot blasters propel media, most often steel shot, at a high velocity toward the surface to be treated. Te media fractures the surface layer of the concrete, taking with it any dirt, coatings, or other contaminants. With the aid of a connected dust collector, the media and debris from the surface are rebounded up and through the separator. Te separator removes the debris back to the dust collector while the media is circulated back into the system for reuse. Blast Pro manufactures portable shot blasting equipment as well as large, ride-on models for use on larger jobs, such as bridge decks, runways, and roads. Blastrac is another company that manufactures shot blast equipment for both large and small jobs. According to Rippman of Blastrac, shot blasting is a cost-efective and environmentally friendly method for preparing concrete surfaces. Shot blasters can achieve surface profles that range from light etching or scratching to the aggressive removal of surface aggregate. "Tis labor- and time-saving process strips, cleans, and profles simultaneously. Diferent surface profles can be achieved by varying shot size, shot fow rate, and machine travel speed. Shot blasting produces excellent bonding characteristics that promote maximum foor life and reduced coating failure," said Rippman. Blastrac ofers a full line of walk-behind and ride-on shot blasting equipment, as well as grinders, scarifers, and dust collectors. When preparing substrates, such as the grinding shown here by Blastrac, you may consider a dust collector. This can collect the rebounded material and possibly separate the media out to be recycled and reused. "Proper preparation is like an affordable insurance policy. Contractors and facility owners can sleep a little better at night knowing that their coating or overlay system has the best chance for success," said Jonn Rippman of Blastrac.

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