BlastOne

Test for Dust Contamination on a Blasted Surface

Any dust which remains on blasted surfaces may reduce coating adhesion and the life of your coatings

Dust naturally accumulates in corners and on horizontal surfaces. Inspection of these areas and other cavities should be undertaken before proceeding with painting.

The best cleaning method is to blow down any blasted surface using compressed air (many contractors will turn the abrasive off and use the blast hose/nozzle). Then some contractors will use small vacuum wands (not unlike household vacuum lances) to perform ‘fine cleaning’ prior to painting. A good method we have seen is to use the large vacuum you may use for bulk abrasive collection and split the large 4” - 8” vacuum hose down into multiple 2” vacuum lines by using a special vacuum hose splitter.

When ‘fine cleaning’ is completed, the surface should be tested for dust in multiple areas The International Standard – ISO8502-3 "Part 3 assessment of dust on steel surfaces prepared for painting – pressure-sensitive tape method" follows the prescribed method.

Kits designed for measuring surface contamination are available here.

The Test Procedure

STEP 1

Dust Test Procedure Step 1

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).

STEP 2

Dust Test Procedure Step 2

Remove the tape from the test surface, place on display board and adhere tape to board.

STEP 3

Dust Test Procedure Step 3

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.


Surface Impurities: Slag Abrasive vs. Garnet Abrasive

There is much talk in the industry about different abrasives and their effect on coating life. After 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”.

Garnet to Slag Test
Steel plate blasted with Coal Slag (left) and GMA Garnet (right).

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 SpeedBlast Garnet.