I. Why do anti-corrosion coatings develop cracks?
① Cracks typically appear during the curing and drying of the coating. If the coating experiences large temperature variations during drying, the cohesive forces between the inner and outer layers of the coating become inconsistent, which can lead to cracking.
② The coating film thickness is significantly excessive. For example, with a standard inorganic zinc silicate primer, if the coating thickness exceeds 120 μm after a single application, the coating is in a high color and gloss state, with high internal stress, making it prone to cracking.
③ Incorrect coating system design. For example, if the first layer is a soft coating and relatively thick, the subsequent layer should be a hard coating.
④ The hydrolysis and polymerization reaction of the inorganic zinc-based primer is incomplete.
⑤ The roughness after sandblasting or shot blasting is insufficient, or the peaks and edges of the surface profile do not meet the requirements of special coatings.
⑥ Insufficient mixing. If the inorganic zinc-rich primer contains a high zinc powder content, improper mixing during application can cause the zinc powder to settle, resulting in uneven coating and potential cracking of the coating film.
II. How to prevent corrosion coatings from cracking
① Strictly manage film thickness, controlling wet film and preventing coating from becoming excessively thick. once the coating is sufficiently thick, it should be allowed to fully dry before applying a second coat. If the subsequent coating dries quickly, control the application interval. If the required film thickness is high and it is difficult to control the application, apply two coats instead.
② Design the coating system correctly. It is not permissible to apply rigid coatings over flexible, extensible coatings.
③ Carefully master the key construction points for inorganic zinc silicate coating: Ensure the coating thickness does not exceed the specified limit, but also ensure complete hydrolysis and polymerization reactions to prevent the formation of fine cracks. During the curing period, increase the ambient humidity or use the spraying method on the coating surface to prevent fine cracks or heal them. If the coating is too thick, it will cause excessive stress during drying, leading to cracking. Therefore, it is essential to strictly control the wet film thickness. High ambient temperatures during construction can cause the coating to dry too quickly, leading to cracking. When spraying, appropriate dilution can be used to reduce the rate of volatilization and drying.
Three. How to deal with cracks in heavy-duty anti-corrosion coatings.
① For coatings with minor cracks, it is necessary to repair them as soon as possible to prevent further development into large-scale cracking.
② For fine cracks, use sandpaper to smooth the surface. For cracks and fissures, use abrasive tools to smooth and level the surface. After treating the cracked surface, repainting is required. If the cracking is caused by a hard exterior paint, use a softer exterior paint and repaint after smoothing.