Technical - ASTM D 4541 & ISO 4624 Adhesive adhesion tester

This presentation explains about the Pull-Off adhesion test for testing the strength of the adhesive used for the installation of tile / stones. This test method covers a procedure for evaluating the pull-off strength (commonly referred to as adhesion) of a coating system from metal substrates.

The test determines either the greatest perpendicular force (in tension) that a surface area can bear before a plug of material is detached, or whether the surface remains intact at a prescribed force (pass/fail). Failure will occur along the weakest plane within the system comprised of the test fixture, adhesive, coating system, and substrate, and will be exposed by the fracture surface. This test method maximizes tensile stress as compared to the shear stress applied by other methods, such as scratch or knife adhesion, and results may not be comparable.

Watch the video for testing procedure:

Many thanks to google.com and doc88.com from where the details have been collected.

What does standard says – about how should be the bond strength?

1. For tile adhesive, as per Indian standard IS 15477 – 750N - 0.13 N/Sqmm.
2. For tile adhesive, as per BS EN 12004 – 0.5 N/Sqmm.
3. For tile adhesive, , Australian Standards 2358 "Adhesive for Ceramic Wall Tile" which fixes a minimum tensile bond strength of cement based adhesives after seven days.  This bond strength requirement is a minimum of 0.15 MPa (22 psi).
4. ASTM F 1147-05 – Adhesion to substrate shall be >20 Mpa
5. CSA A23.1 gives a minimum bond strength for toppings of 1.0 MPa (145 psi)
6. Tensile adhesion strength as per Singapore HDB method shall be of - average strength  > 0.80 N/Sqmm and individual strength  > 0.60 N/Sqmm
7. BS EN 1015

ASTM D4541, “Pull-off Strength of Coatings Using Portable Adhesion Testers” - Different testers may yield different pull-off values

1. Annex A1: Fixed Alignment Type II (mechanical)
2. Annex A2: Self Aligning Type III (hydraulic)
3. Annex A3: Self Aligning Type IV (pneumatic)
4. Annex A4: Self Aligning Type V( hydraulic)
5. Annex A5: Self Aligning Type VI (hydraulic)

Do we need to test the bond strength?

1. Thicker material may give the value of cohesive strength (Inner-strength of a material) not the bond strength of material with the substrate.
2. May produce misleading pull-off values (false, high).
3. Scoring through material (down to the surface) and value may be of cohesive strength of surface.
4. Test specimen may get disturbed while fixing dolly OR at the time of fixing the machine attachments and reading may vary.
5. Force / load application in un-uniform way may vary the readings.
6. Since all surface are not homogeneous, reading will vary and the dolly shall be larger in size.
7. The readings may be of bond strength of surface not of the material.
8. In general, if the surface has high compressive strength will have low surface tensile strength… readings will be very low.
9. Readings will be of min value, but actual bond strength of material will remain unknow.
10. Pull-off strength / bond strength data is not typically a predictor of subsequent application performance.
11. No industry is having adhesion acceptance value.
12. Pull-off adhesion (resistance to perpendicular pull), requires specialized equipment and value cannot comparable, since testing mechanisms are different than the site level.