What is a gypsum plasticiser?

01.09.2024 · Valerii Korolko · 3 min read

How plasticisers work

Plasticisers act at the microscopic level, reducing the cohesive forces between gypsum particles and water. This makes it possible to reduce the amount of water in the mixture without losing plasticity. Plasticisers also extend the working time of the mixture, improve its flowability and prevent cracking during drying.

Phosphates alter the crystallisation process, allowing better control of hydration. They help distribute water more evenly in the gypsum mixture, reducing the amount it needs while maintaining fluidity. As a result, the gypsum product is denser and stronger, with fewer air pockets and voids.

Sodium, potassium and ammonium phosphates are often used as plasticisers in low concentrations, usually less than 1% of the dry weight, to ensure optimal performance without adverse effects.

Benefits of use

Increased strength: they increase the final strength of products by promoting better crystallisation.
Improved workability: they improve the plasticity of the mixture, making it easier to shape and apply.
Reduced water demand: they help reduce the amount of water required in the mixture without compromising its workability.
Durability: gypsum products with phosphate additives are more resistant to wear, shrinkage and cracking.

Applications

Phosphates are commonly used in specialised gypsum applications:

– Casting and moulding: where strength and fine detail are required.

– Construction materials: to improve the strength and performance of building materials (plasterboard or plaster).

Application recommendations

When using phosphates as a plasticiser, it is important to measure and control the dosage carefully to avoid excessively accelerating the setting time, as this can lead to poor workability or structural defects.

Phosphates are a versatile and effective means of improving the properties of gypsum, especially where greater strength and durability are required.

How to choose the right plasticiser

Purpose – determine what you need the gypsum mortar for (moulding products, plaster, self-levelling floors, etc.).
Type – the plasticiser must be compatible with the specific type of gypsum.
Operating conditions – take into account the temperature and humidity of the environment in which the gypsum products will be used.

Defects caused by using low-quality phosphates as gypsum plasticisers

Uneven crystallisation: low-quality phosphates cause uneven hardening, resulting in cracks and voids.
Hardening that is too fast or too slow: an uncontrolled reaction accelerates or slows down the hardening process, which complicates the work and may lead to a loss of plasticity or make it impossible to give the product the required shape.
Reduced strength: instead of increasing strength, low-quality phosphates can weaken gypsum products, making them brittle and less resistant to mechanical loads.
Stains or discolouration: some low-quality phosphates may contain impurities that can cause stains or discolouration on the surface of products.
Impaired adhesion: improper interaction between the gypsum components and low-quality phosphates impairs bonding with other materials, which reduces the quality of finishing work.
Chemical instability: impurities in low-quality phosphates cause chemical instability in the gypsum mortar, which subsequently leads to its deterioration.

Thus, using low-quality phosphates can not only reduce the quality of gypsum products but also lead to significant financial losses due to the need to redo the work or replace the material.

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