AS-3894.9-2003.pdf

1 AS 3894.92003 © Standards Australia Australian Standard TM Site testing of protective coatings Method 9: Determination of adhesion PREFACE This Standard was prepared by the Australian members of the Joint Standards Australia/Standards New Zealand Committee CH-003, Paints and Related Materials. After consultation with stakeholders in both countries, Standards Australia and Standards New Zealand decided to develop this Standard as an Australian Standard rather than an Australian/New Zealand Standard. FOREWORD The measurement of a coatings ability to adhere or bond to the surface to which it has been applied and the intercoat adhesion between subsequent layers of previously applied coatings are major factors when determining a maintenance schedule or writing a maintenance specification for a structure. The onsite measurement of adhesion will over a period help to determine the degree of urgency or programming of a maintenance processes when protecting a structure from atmospheric or other corrosive elements in its own environment. METHOD 1 SCOPE This Standard provides a method for evaluating and testing the adhesion of existing coating systems to their substrate while in their service environment. 2 DEFINITIONS For the purpose of this Standard, the definitions in AS 2310 apply. 3 REFERENCED DOCUMENTS The following documents are referred to in this Standard: AS 1580 Paints and related materialsMethods of test 1580.408.4 Method 408.4: Adhesion (cross-cut) 1635 Methods of test for pressure-sensitive adhesive tape 1635.3.1 Part 3.1: Adhesion strength AS 3894.9 Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 AS 3894.92003 2 Standards Australia www.standards.com.au AS 3894 Site testing of protective coatings 3894.3 Part 3: Determination of dry film thickness 3894.7 Part 7: Determination of surface temperature AS/NZS 2310 Glossary of paint and painting terms 4530 Coated abrasiveCloth rolls 4 APPLICATION 4.1 General Three methods of assessing the adhesion or bonding of a coating system to its substrate are referred to as Methods A, B and C described in Clauses 5, 6 and 7. Methods A and B are qualitative and Method C is quantitative. Because Methods A and B are analogous, the reliability of the test results will be confirmed if both methods are conducted and compared at the same time. Because Method C, Pull-off, may take several days for the test to stabilize under field conditions, it is not recommended that the test be used for routine quality control. All three test methods will damage the coating system. A repair specification should be available to repair the coating if it is to be placed back into service. Because the adhesion, hardness and flexibility of most coatings will vary with changes in temperature, testing is best performed within the temperature range of 1525°C. Should the operating temperature or the temperature at the time of testing be outside this range, the manufacturers advice should be sought. If adhesion fails between coats (inter-coat adhesion) in a multi-coat system, the adhesion of the coating system to the substrate cannot be determined with reliability. 4.2 Sampling plan This method recommends a number of randomly selected locations to be tested. It is further recommended that either Method A or B be conducted depending on the film thickness (see Clause 6.1). For structures (a) 10 m2 or less1 test site; (b) greater than 10 m2 and less than 30 m2 2 test sites; (c) greater than 30 m2 and less than 100 m2 3 test sites; and (d) exceeding 100 m23 test sites plus 1 test site for each additional 100 m2. 5 METHOD A KNIFE TEST 5.1 Principle The previously applied coating is cut through to the substrate surface in the manner described and the ease with which the coating can be removed is determined. Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 3 AS 3894.92003 www.standards.com.au Standards Australia 5.2 Apparatus 5.2.1 Knife blade A sharp edged, freshly honed knife blade having a sharpened point of 45° or less, for example, a scalpel or blade holder containing snap-off disposable blades. NOTE: A knife with a more substantial blade may be required for ultra-high-build coatings and some high-build coatings. 5.2.2 Surface temperature thermometer As specified in AS 3894.7. 5.2.3 Straightedge Approximately 100 mm long. 5.2.4 Film thickness gauge As specified in AS 3894.3. 5.3 Test conditions The test should be performed under normal operating conditions with details of the surface temperature and other environmental factors being recorded. 5.4 Intersecting cut method The procedure is as follows: (a) Determine the dry film thickness (DFT) of the target test area in accordance with an appropriate method from AS 3894.3. Record the DFT. (b) Hold the blade against the straightedge and at right angles to the coated surface. Incline the blade at an angle of 45° in the direction of the cut and using a single stroke, scribe a cut 25 mm long through to the substrate. (c) Make a second cut as in Step (b), intersecting the centre of the first cut to form two 30°45° vees. (d) Using the point of the blade, gently try to lift or prise the coating from the intersection of the vee. Do not apply force to the point of the blade. (e) Assess the adhesion by applying a rating from Table 1 and record the result. TABLE 1 ADHESION RATING OF COATING (INTERSECTING CUT) Rating scale Appearance 0 No removal 1 Slight trace of peeling or removal at intersection 2 Jagged removal of up to 1.5 mm at intersection 3 Jagged removal of up to 3.0 mm at intersection 4 Coating easily removed in the area up to 15 mm either side of the intersection of the cuts 5 Removal continues greater than 15 mm beyond the cut Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 AS 3894.92003 4 Standards Australia www.standards.com.au 5.5 Report The report shall include the following information: (a) Name of testing organization. (b) Date of testing and report number. (c) Identification and description of the test item and its coating system, substrate details and method of surface preparation of the substrate. (d) Dry film thickness of the coating system and its age. (e) Test Intersecting cut, description of blade and the location of the test. (f) Test conditions including surface temperature. (g) Rating and comments. (h) Reference to this Australian Standard, i.e., AS 3894.9. (i) Any deviations from this test method. 6 METHOD BCROSS-CUT 6.1 Principle The previously applied coating is cut through to the substrate surface in the cross-cut or cross-hatched manner described and the adhesion of the coating system is assessed by applying and removing a piece of pressure-sensitive tape from the cuts. The area of coating disturbed or disbonded by the tape is determined. The test is suitable for coatings with a dry film thickness in the 50 µm125 µm range. Tests performed on DFTs outside this range may be unreliable. 6.2 Apparatus 6.2.1 Knife blade or cross-cutter A sharp edged tool, e.g., a scalpel or blade holder containing snap-off disposable blades. NOTES: 1 One or more passes with a blade may be required for some high-build coatings. 2 Proprietary cross-hatch cutters that comply with this Standard and AS 1580.408.4 should be used. 6.2.2 Surface temperature thermometer As specified in AS 3894.7. 6.2.3 Straightedge Approximately 100 mm long. 6.2.4 Film thickness gauge As specified in AS 3894.3. 6.2.5 Tape Transparent, 24 mm wide pressure-sensitive tape tested in accordance with AS 1653.3.1 and having a minimum adhesion strength of 6.0 N/24 mm width and a maximum adhesion strength of 7.5 N/24 mm width. NOTE: Because the adhesive properties of the tape change over time, the tape should be freshly purchased with a shelf life not exceeding 18 months. Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 5 AS 3894.92003 www.standards.com.au Standards Australia 6.2.6 Brush A clean soft-haired brush. 6.3 Test conditions The test should be performed under normal operating conditions with details of the surface temperature and other environmental factors being recorded. The test surface has to be clean and free of all oil, grease, contaminants and other debris. 6.4 Cross-cut method The procedure shall be as follows: (a) Determine the dry film thickness (DFT) of the target test area in accordance with an appropriate method from AS 3894.3. Record the dry film thickness. (b) Hold the blade against the straightedge and at right angles to the coated surface. Incline the blade to an angle of 45° in the direction of the cut and using single strokes, scribe six (6) parallel cuts 2 mm apart and 25 mm long, through to the substrate. (c) Lightly brush the cut area to remove any detached flakes or ribbons of the coating. (d) Repeat the 6 cuts as in Step (b), but this time at 90° to and centred across the original cuts to form a grid. (e) Brush the surface to clear all debris from the cross-hatched area. (f) Remove outer layer of tape from the roll to expose fresh tape then carefully remove in one motion and apply a 75 mm length of tape across the grid and parallel to one of the cuts so that it protrudes equally on both sides of the grid. (g) Use the finger to press the tape smoothly onto the surface. This will be indicated by the wet-look colour change beneath the tape. (Refer Figure 1.) (h) After 90 ±15 s, remove the tap from the grid by rapidly pulling (0.51.0 s) a free end in a single smooth motion and at an angle of 60° to the direction of the pull. (Refer Figure 2.) (i) Inspect the grid for removal of the coating from the substrate or from a previous layer of the coating and classify in accordance with the scale in Table 2. (j) Repeat the test at two other sites. FIGURE 1 POSITION OF TAPE WITH RESPECT TO GRID Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 AS 3894.92003 6 Standards Australia www.standards.com.au FIGURE 2 POSITION OF TAPE IMMEDIATELY PRIOR TO REMOVAL FROM GRID TABLE 2 CLASSIFICATION OF TEST RESULTS (CROSS-CUT) Classification Description Appearance of surface at cross-cut 0 The edges of the cuts are completely smooth; none of the squares of the lattice is detached 1 Detachment of small flakes of the coating at the intersections of the cuts. A cross-cut area not distinctly greater than 5% is affected 2 The coating has flaked along the edges, at the intersections of the cuts, or at both locations. A cross-cut area distinctly greater than 5%, but not distinctly greater than 15% is affected 3 The coating has flaked along the edges of the cuts partly or wholly in large or different parts of the squares, or both have occurred. A cross-cut area distinctly greater than 15%, but not distinctly greater than 35% is affected 4 The coating has flaked along the edges of the cuts in large ribbons, some squares have detached partly or wholly, or both have occurred. A cross-cut area distinctly greater than 35%, but not distinctly greater than 65% is affected 5 Any degree of flaking greater than classification 4 6.5 REPORT The report shall include the following information: (a) Name of testing organization (b) Date of testing and report number. (c) Identification and description of the test item and its coating system, substrate details and method of surface preparation of the substrate. (d) Dry film thickness of the coating system and its age. (e) Test Intersecting cut, description of blade and the location of the test. Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 7 AS 3894.92003 www.standards.com.au Standards Australia (f) Test conditions including surface temperature. (g) Rating and comments. (h) Reference to this Australian Standard, i.e., AS/NZS 3894.9. (i) Any deviations from this test method. 7 METHOD C PULL-OFF TEST 7.1 Scope This test field test method quantifies the perpendicular force or tensile pull required to disbond or detach a coating system from a substrate. The test directly measures the tensile adhesion of the coating system to the substrate under operational conditions. The method is suitable for quantifying the adhesive or bonding qualities of a coating system to most rigid substrates including steel, aluminium, concrete and masonry. 7.2 Principle This method uses a mechanical or hydraulic pull-off adhesion tester or load cell connected to a dolly or thimble which has previously been glued to the test coating. A perpendicular force is applied by the adhesion tester to the dolly until (a) the coating disbonds from the substrate; (b) there is cohesive failure within the coating; (c) there is an intercoat adhesion failure; or (d) a specified force has been reached. The adhesive chosen to bond the dolly to the surface has to be fully cured and have a tensile bond strength greater than that anticipated between the coating and the substrate. 7.3 Apparatus 7.3.1 Adhesion tester Instruments, which include a supply of specialized dollies of known cross-sectional area, are commercially available and are designed to couple into the chuck of the tester. The tester has to be able to be reset to zero after each use and has to have an order of accuracy of ±15%. 7.3.2 Surface temperature thermometer As specified in AS 3894.7. 7.3.3 Adhesive A suitable high-strength solvent-free adhesive that does not interact with the coating and has a tensile bond strength greater than the test requirement. A typical adhesive is a solvent- free 2-pack high-strength epoxy adhesive. 7.3.4 Film thickness gauge As specified in AS 3894.3. 7.3.5 Circular hole cutter A tungsten-carbide-tipped keyhole cutter that has a slightly larger diameter than the dolly and is suitable for use in an electric hand drill. Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 20 May 2008 AS 3894.92003 8 Standards Australia www.standards.com.au 7.3.6 Abrasive cloth P220 emery cloth that complies with AS/NZS 4530, to smooth and abrade the surface to which the dolly is to be bonded. 7.3.7 Solvent A suitable solvent such as acetone, to degrease the test site prior to abrading the surface and bonding the dolly. 7.4 Test conditions The test should be performed under normal operating conditions with details of the surface temperature and other environmental factors being recorded. The surface should be clean, to ensure it is free of all debris and contaminants. 7.5 PROCEDURE 7.5.1 Adhesion tester The procedure is as follows: (a) Select the adhesion tester that has a scale of force values most appropriate for the coating system to be tested. (b) Determine the dry film thickness (DFT) of the target test area in accordance with an appropriate method from AS 3894.3. Record the DFT. (c) Degrease the target surface with solvent, then thoroughly abrade the surface of the coating to remove all gloss using emery cloth. Again swab the surface with solvent using a clean cotton wipe. (d) Prepare the adhesive in accordance with the manufacturers directions and apply to the test dolly. If using a two-pack