HPMC, also known as hydroxypropyl methylcellulose, is a commonly used additive in various industries. In the construction industry, HPMC is widely used in cement-based materials such as putty powder, gypsum, and cement mortar. HPMC plays an important role in improving the performance of putty powders by imparting good workability, cohesive strength and water retention properties. However, when HPMC is applied to putty powder, a phenomenon called “foaming” occurs. In this article, we explore the causes of blisters and discuss ways to prevent them.
What is blistering and why does it happen?
Blistering is the phenomenon of air bubbles or blisters on the surface of putty powder after construction. This may happen immediately after application or after some time, depending on the underlying cause. Blistering can be caused by a number of factors including poor substrate preparation, application under adverse environmental conditions or use of incompatible materials. The reasons for the foaming of HPMC and putty powder are as follows:
1. Incompatibility between HPMC and other additives: HPMC is often used in conjunction with other additives such as superplasticizers, retarders, and air-entraining agents. However, if these additives are incompatible with each other, foaming can result. This occurs because the additives interfere with each other’s ability to perform their intended function, resulting in an unstable mixture and poor adhesion to the substrate.
2. Insufficient mixing: When HPMC is mixed with putty powder, proper mixing is very important. Inadequate mixing can cause the HPMC to clump together and form islands in the mixture. These islands create weak spots on the surface of the putty powder, which can cause blisters.
3. Water retention: HPMC is famous for its water retention, which is good for putty powder. But if the putty powder gets too much moisture, it will cause blistering. This usually happens when putty powder is used in high humidity conditions or on surfaces that have not cured properly.
4. Poor application technique: Poor application technique can also cause blistering. For example, if putty is applied too thickly, it may trap air pockets beneath the surface. These air bubbles can then expand and cause foaming. Likewise, if putty is applied too quickly or with too much force, it will form a weaker bond with the substrate, which can also cause blistering.
How to Prevent Blistering
Preventing foaming when using HPMC and putty powders requires careful attention to the materials, techniques and environmental conditions involved. Here are some tips for preventing blisters:
1. Choose compatible additives: When using HPMC, it is important to choose additives that are compatible with each other. This helps ensure that the mixture is stable and that each additive performs its intended function without interfering with the others.
2. Stir evenly: HPMC should be fully mixed with putty powder to ensure even distribution. This helps prevent lumps and weak spots on the surface of the putty powder.
3. Moisture control: Moisture control is crucial when using HPMC and putty powder. Make sure that the putty powder does not come into contact with excessive moisture during construction, and avoid construction under high humidity or wet conditions. If necessary, use a dehumidifier to reduce the moisture content in the air.
4. Use Proper Application Technique: Proper application technique will also help prevent blistering. Apply the putty powder in a thin, even layer and apply it to the substrate with a trowel or other suitable implement. Avoid applying putty powder too thickly, too quickly or with too much force.
5. Consider the substrate: The substrate on which the putty powder is applied also affects the risk of blistering. Make sure the substrate is properly cured, cleaned and prepared before applying putty powder. If necessary, a primer can be used to improve the bond between the substrate and the putty powder.
In conclusion, blistering can be a frustrating and unsightly problem when working with HPMC and putty powder. However, this situation can be prevented with due attention to the materials, techniques and environmental conditions involved. By choosing compatible additives, mixing well, controlling moisture, using proper application techniques, and considering the substrate, you can ensure a smooth, bubble-free finish every time. As a leading HPMC manufacturer, we are committed to providing high-quality products that meet our customers’ needs. We hope this article has been helpful in understanding why HPMC and putty powder foam and how to prevent it.