How do I test for embedded dust contamination on my blasted surface?
Any dust which remains on blasted surfaces may reduce coating adhesion and subsequently the life of your coatings. Dust naturally accumulates in corners and on horizonal surfaces. Inspection of these areas and other cavities should be undertaken before proceeding with painting. The International Standard – ISO8502-3 "Part 3 assessment of dust on steel surfaces prepared for painting – pressure-sensitive tape method" follows the prescribed method.
The Test Procedure
Apply an 8” (200mm) piece of tape to a representative test site. Starting at one end of the tape, maintaining a firm pressure and at a constant speed, move the thumb along the tape 3 times in each direction (each stroke should take 5-6 seconds).
Remove the tape from the test surface, place on display board and adhere tape to board.
Assess the quantity of dust on the tape by visually comparing an area of the tape with equivalent sized areas of the pictorial reference guide. Record the rating (0-5) that closely corresponds to the reference.
Kits designed for measuring surface contamination are available for sale from Blast-One here.
There is much talk in the industry about different abrasives and their effect on coating life. Blast-One has performed extensive testing using different abrasives, and slag abrasive embedment has been proven to be detrimental to coating adherence.
A report written by AW Momber (Author of 'Surface preparation standards for steel substrates - a critical review') in November 2004 stated “There is a significant reduction in adhesion when a slag abrasive is used”. Read the full review here.
Note the impurities, when using slag, that have adhered to the masking tape on the left are only some of the particles that have been captured on the steel. Compare the embedment levels on the sample on the right. This example was blasted using Blast-One SpeedBlast Garnet.