Causes of Cracking and Spalling in Putty Powder and Corresponding Remedial Measures
Release Time:
2020-10-23
Source:
Causes of Cracking and Spalling in Putty Powder and Corresponding Remedial Measures
Putty cracking
Phenomenon: Cracking on the surface of the putty after a period of application.
Cause:
1. Construction shall not commence until the substrate has been thoroughly dried; the substrate moisture content must be ≤10%.
2. If the base putty is not fully dry before applying the finish coat, the surface layer will dry first while the underlying layer is still in the drying process, resulting in uneven shrinkage between layers and making cracking more likely.
3. During substrate preparation, if the joint-filling and leveling materials are not completely dry before applying a harder interior wall putty, cracking is likely to occur.
4. If the coating is applied too thickly, the interior dries more slowly while the surface dries more quickly, which can also lead to cracking.
Solution:
1. Cracked putty must be removed. If the cracks are relatively small, a flexible putty can be used for the first coat, followed by application in accordance with the relevant construction specifications.
2. Each coat of application should not be too thick, and the interval between successive coats must be at least 4 hours. Only after the previous coat of putty has completely dried may the subsequent coat be applied.
Putty detachment
Phenomenon: Poor bond strength between the putty and the substrate, resulting in direct detachment from the substrate.
Causes:
1. The existing wall surface is very smooth (e.g., tempered putty, polyurethane, or other oil-based paints), resulting in poor adhesion between the putty powder and the surface.
2. The new wall surface was cast using formwork, resulting in a smooth finish that contains a large amount of release agent (waste engine oil or silicone-based compounds).
3. When putty is applied directly to non-mortar substrates such as wood-based and metal substrates (e.g., plywood, multilayer board, particleboard, solid wood), differences in surface expansion and contraction combined with the high water absorption of these materials can prevent rigid interior wall putty from accommodating such movement, typically resulting in delamination after about three months.
4. If the putty has exceeded its shelf life, its bond strength will decrease.
Solution:
1. Remove the loose layer and address it specifically according to the following situations:
2. Sand the existing wall surface to increase its roughness, then apply a bonding agent (prepared by mixing 10% eco-friendly adhesive or a dedicated interface agent).
3. Use an oil-removal cleaning agent to remove release agents or other oily residues from the surface before applying the putty.
4. Apply a two-component or dedicated plywood filler for construction.
5. For exterior wall surfaces such as marble, mosaic, and ceramic tiles, please use exterior renovation putty as the primer.
6. Use within the putty’s shelf life.
