Page 352 - Construction Waterproofing Handbook

8.12 CHAPTER EIGHT

FIGURE 8.9 Abrasive (shot-blast) cleaning process. (Courtesy
of Devcon)

tip. Water pressure then directs the aggregate against a substrate. This method operates
under lower pressures than compressed air-blasting equipment and also wets the aggre-
gate, keeping airborne contaminants to a minimum.
With all abrasive cleaning, some portion of a substrate surface will be removed. Careful
testing should be completed to analyze the process before complete substrate cleaning.
Additionally, because of potential damage and safety concerns, only highly experienced
mechanics should be employed in these cleaning processes.
By using extremely small aggregates, substrate damage is lessened but still produces
desired cleaning results. A very fine powdered sand referred to as flour sand because it has
the consistency of baking flour, is available. By using this sand with low pressures, satis-
factory results with insignificant substrate damage are possible.
Sanding and mechanical wheel grinders are used to remove paint and corrosion from
metal substrates. Grinders also have limited usage on concrete substrates for removing
small contaminated areas of oil, grease, and other accumulations, which pressure cleaning
will not remove. This cleaning also removes portions of the substrate and should be used
only when other alternatives are not available. (See Table 8.2.)

TABLE 8.2 Abrasive Cleaning Properties
Advantages Disadvantages
Removes paint layers easily Can damage substrate excessively
Flour sand reduces damage Safety concerns
Variable pressures Equipment required