Discover effective ways to increase plaster setting times easily and adapt your project to your needs. Explore our guide for better results today.
Plastering is an essential part of the construction process that requires skill, patience and precision. For trade plasterers, understanding the nuances of plaster setting time is critical and can significantly increase the efficiency of jobs.
While fast-setting plaster might seem like a time-saving solution, slowing down the setting process can often be better. From laying more on at one time, to not rushing on the more intricate areas, there are several reasons why slower setting times are advantageous.
This article explores how to increase plaster setting times, factors that influence the process, and practical tips to slow down setting times effectively.
The Science of Plaster Setting
Gypsum Plaster is primarily calcium sulphate hemihydrate which is combined with water before application. When mixed with water a slurry is formed and a chemical reaction occurs, causing the plaster to begin to harden and eventually set hard.
The setting process is divided into two stages:
Initial Setting: The plaster begins to harden but remains workable (typically 2 hours from hydrating to set)
Final Setting: The plaster has solidified completely and requires time to fully set and dry (can be many hours, or days depending on the conditions)
For the purposes of this blog we will focus on the initial setting time.
While modern plastering materials often promote faster drying times for efficiency, there are significant benefits to slowing this process.
Why Slower Plaster Setting is Better
Why should you slow down plaster setting? Well, there are very good reasons for it. Here they are:
1. Improved Workability
Slower setting times give plasterers more time to work with the material. This is particularly beneficial for:
Large Areas: Covering extensive areas without rushing
Complex Projects: Achieving intricate finishes like curved edges, angles, or decorative details
2. Reduced Cracking
Rapid setting can cause the plaster to dry unevenly, increasing the risk of cracks. Slower setting times allow the material to dry more uniformly, minimising stress on the surface. This is particularly important for:
Older Walls: Where structural movement or settling might occur
High-Humidity Areas: Such as bathrooms and kitchens, where rapid drying could lead to shrinkage and cracks
A smoother and crack-free surface not only looks better but also lasts longer.
3. Enhanced Adhesion
Slower drying allows the plaster to bond more effectively to the underlying surface. This ensures a strong and stable plaster application, reducing the likelihood of:
Delamination: When the plaster separates from the substrate
Peeling or flaking: Common issues with improperly adhered plaster
For areas that require a durable finish, such as ceilings or high-traffic walls, slower setting times are a critical factor.
4. Better Finish Quality
Plaster that sets too quickly can become difficult to manipulate, leading to rough textures or visible seams. With slower setting times, there's ample opportunity to:
Achieve seamless edges:Â Blend plaster layers for a uniform appearance
Perfect the texture: Whether aiming for a smooth finish or decorative pattern
A flawless finish is essential for both aesthetics and functionality, especially in visible areas like living rooms or commercial spaces.
5. Increased Control for Beginners
For novice or less experienced plasterers, a slower setting time can be a lifesaver. It provides:
More time to correct mistakes: Whether it's adjusting thickness, smoothing out bumps, or reshaping edges
A less stressful experience: Rushing through the process often leads to frustration and subpar results
By allowing more time for adjustments, slower plaster setting times make the learning curve less steep.
Factors That Influence Plaster Setting Times
Several variables affect how quickly plaster sets. Understanding these factors can help you take steps to control the process.
Type of Plaster
Fast-Setting Plaster: Designed for quick jobs, often sets within 60 - 90 minutes.
Standard Finishing Plaster: Takes 120 minutes to set.
Specialty Plaster: Some types, like lime-based plaster, set much slower.
Temperature
High temperatures accelerate the setting process. Cool environments slow it down, giving you more working time.Â
Humidity
Low humidity causes plaster to dry faster. Higher humidity levels extend setting times.
Mixing Proportions
Using less water leads to faster setting. Adding extra water slows down the process but may weaken the plaster if overdone.
Additives
Retarders like Extratime Please Retarder can slow the setting process predictably without causing any issues with the finish plaster. Accelerators like Halftime Plaster Accelerator speed it up.Â
Substrate Type
Porous surfaces absorb water from the plaster, causing it to set faster. Non-porous surfaces slow down the drying process.
Tips to Increase Plaster Setting Times
If you're looking to slow down the setting process, here are practical tips to help. They will ensure better plaster workability as well.
1. Control the Environment
Work in a cool, shaded area to avoid heat accelerating the process. Use a humidifier to maintain higher moisture levels in the air.
2. Use Retarders
Additives like Extratime Plaster Retarder are effective at slowing down the chemical reaction. They not only slow the setting time but can improve the strength and adhesion properties.Â
3. Add More Water to the Mix
Using slightly more water in the mixture can extend setting times. However, ensure you don't compromise the strength of the plaster by overwatering.
4. Prepare the Substrate
Preparing the substrate with PVA, SBR or commercially available pre-grit products before applying plaster will reduce water absorption and control the setting process.
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When Faster Setting Times Might Be Necessary
While slower setting times have numerous advantages, there are scenarios where quick setting is more practical.
Time-Sensitive Projects: Deadlines or emergencies may require fast-setting plaster
Small Areas: For repairs or touch-ups, quick drying can save time without compromising quality
Cold Weather: When working in cold conditions, fast-setting plaster can counteract the slower drying caused by low temperatures
In such cases, using accelerators or fast-setting materials is a better choice.
Increase Plaster Setting Times To Improve Plaster Workability
Whether you're a seasoned contractor or a DIY beginner, understanding how to increase plaster setting times is a valuable skill that pays off in better outcomes and reduced stress. If you need help with slowing down plaster setting, check out plaster retarder products from Eazymix.Â
Our products are created by the trade for the trade. Both plaster retarder and accelerator options are available for your plastering job. Check out our online catalog and see which product works best for you.