CoatingsPro Magazine

MAY 2019

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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COATINGSPRO MAY 2019 63 Within one year, the paint was sponta- neously delaminating. Adhesion tests were performed, and all patched areas, which were numerous, failed. In every instance, it was noted that some of the patching material stayed adhered to the rear of the delaminated paint while some remained on the wall. e client called me in to investigate this failure. Testing, Testing My investigation involved several field tests. Painting contractors should perform these tests before starting a job to avoid expensive failures later on. Several standards from the Painting and Decorating Contractors of America (PDC A) provide guidance on painting tilt-up construction. PDC A P17, "Field Painting of Smooth-Faced Tilt-Up Concrete," states that prior to applying coatings, the painting and decorating contractor should deter- mine the pH of the surface of both the smooth-faced tilt-up concrete and the patching material. pH is a measure of the acidity or alkalinity of a substance. ASTM D4262 describes the proce- dure for pH measurement. A pH of 7 indicates neutrality, while readings below 7 indicate increasingly acidic conditions, and pH readings above 7 indicate increasingly alkaline conditions. e pH of properly cured cementitious products, like concrete or stucco, is in the range of 8 to 10. Higher numbers could indicate an improper mix or cure or the presence and migration of moisture. e pH on the surface of the concrete and patch should be determined by marking the area with a pH pencil, moistening the area with distilled water, and comparing the color to a pH chart. Coating application should not be initiated until the surface pH is within the manufacturer's recommended range for the specified coating system. If the pH is higher than 10, the concrete or patch may not be fully cured. High substrate pH can lead to paint failures such as alkali burn and saponifica- tion. Photo 4 shows a highly alkaline substrate in this particular case, which indicates that the patching compound had not completely cured. PDC A P4 states that while the contracting entity has the respon- sibility to determine that a surface is complete and that the "quality of appearance" is such that it is ready for finish painting or wallcovering, the painting and decorating contrac- tor is required to inspect surfaces to determine, by reasonable and visible evidence, that the finish coat will satis- factorily adhere to the surfaces and will perform as specified. One such visual means is a chalk test in which the stability of the patch- ing material is assessed in accordance with ASTM D4214. In this test, a black cloth is rubbed against the surface of the patching material. If a large amount of powder or dust is transferred to the cloth, then multiple chalk tests at the same location should be performed. If each successive test has high levels of chalk transfer, then the patching material is friable and dusting; it is not just superficial powder. If this occurs, do not prime or paint this surface! In my experience, the most Photo 2. A photomicrograph of a cross-section of delaminated paint, showing a layer of patch attached to the rear of the primer. Photo 3. Bubbling behind the paint is a coating failure that could be avoided if proper tests are performed before starting the job. Delaminating Exterior Paint

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