Slowing the Setting Time of Plaster

Methods to delay the setting time of plaster for various applications.

Introduction

The setting time of plaster can be crucial in different applications, especially for intricate work or large surfaces where extended workability is desired. There are several methods to achieve this by using various additives or techniques.

Using Retarders

Retarders are chemical additives that can be added to plaster to slow down its setting time. Common retarders include citric acid and trisodium citrate. These retarders, when mixed with water, make the plaster set slower and offer more time for application and manipulation.

Citric acid is particularly effective, and small amounts will significantly extend the setting time, allowing for a harder and more durable finish.

Traditional Methods: Glue Size

One traditional method involves using glue size, a gelatine-based material made from animal bones. Here's a step-by-step process:

1. Mix the glue size with water and a handful of lime to keep it in a liquid form.
2. Boil the liquid material in a bucket, then allow it to cool.
3. Test the strength by adding one capful of size to the water before adding plaster.
4. Time the set to ensure the desired delay before application.

Considerations

Always ensure that the mixing equipment is clean to avoid contamination, which could adversely affect setting times. Fresh contamination is more problematic than old, so washing equipment immediately after mixing is recommended.

Over-mixing plaster can also waste time and energy and deteriorate workability, making it challenging to achieve a flat finish.

Conclusion

Using these methods, you can effectively manage and slow the setting time of plaster to suit your specific needs. Understanding the role of retarders and traditional techniques can help you achieve a smoother and more manageable plastering process.

For detailed information and more plastering tips, visit the Plastering FX Academy website.