Crusting Agents, Veneering and Surface Stabilisation Chemicals
There are a large range of different chemicals used for crusting / veneering and surface stabilisation. The purpose of these products is to bind the particles on the surface together to prevent them lifting off as dust. Some of the more common applications include, stockpile crusting, tailing dam crusting, embankment stabilisation, preventing erosion of rehabilitation areas and sealing asbestos contaminated building products.
These chemicals are typically polymer-based solutions as they bind the surface particles together with low application rates making them cost effective (low cost per square meter treated). The strength of the polymer bonds, their action with the surface material and their ability to withstand environmental conditions varies between polymer types, polymer quality and application rate. Polymer bonds are generally strong, but brittle. As a result the use of these products is usually limited to areas where there is no traffic as vehicles, human traffic and even animals can break the bonds and damage the surface crust. With many of the polymers once the surface is damaged, wind can get start lifting off dust particles which can expand the area of damage – think peeling of paint.
For all crusting agents the smoother and compact the surface the better the performance.
Most crusting agents have very little colour so it is common for a pigment or dye (usually green) to be added to assist with application and to show that the area has been crusted. Depending on the polymer type and supplier, the colour can be supplied in the crusting agent or purchased separately and added to the solution (polymer diluted in water) before it is sprayed on the ground.
Crusting agents have traditionally been applied with water carts using the rear sprays, top mounted monitors or hoses connected to the carts. Water carts provide a convenient way to get the crusting agent to where it is required, and they also provide a tank where the crusting agent (and colour dye) can be diluted and mixed. There are circumstances such as partly wet or unstable tailings dams where water carts can not access the area that needs to be treated. In these cases, helicopters or planes are used to apply the product and some companies have been trailing drone based application methods.
It is critical when applying crusting agents (regardless of the method) to ensure there is adequate solution (crusting agent diluted in water) applied per square meter. For materials that will absorb water which includes soils and most mineral ores, the depth of the crust is dependent on volume of solution applied. If there is not enough solution, the crust will be thin and easily damaged by weather events. For materials that do not absorb water such as building materials then a stronger solution is used, but less is applied per square meter as it only needs to coat the surface.
Crusting agent types
There are a number of companies selling crusting agents under a multitude of different brand names, but ultimately, they all fall under the following categories.
Hydromulching is simply a way of spraying a mulch onto the surface. Generally, the mulch will contain the crusting agent as well to help stabilise the surface and mulch. The actual crusting agent used in the Hydromulch is usually one of the polymers detailed below.
Hydromulching is also undertaken as part of a seeding process so may also include seed, fertiliser and soil conditioners. Hydromulching is significantly more expensive than using a crusting agent alone, but provides efficiencies and benefits as part of a seeding program. When used purely as a crusting agent it can provide additional protection from extreme weather events, but generally any increase in crust duration is offset by the increase in cost compared to pure use of crusting chemicals alone.
PVA based polymers
PVA polymer-based crusting chemicals are one of the oldest and due to their high availably, low cost crusting agents. The action of PVA is that it creates strong bonds with itself so it tends to create more of a film based crust. Compared to the other polymer it creates relatively weak bonds that when dry are brittle. PVA crusts will soften with water and lose their bond with the material. As a result they are generally only suitable for short terms applications in dry climates.
Acrylic / latex based polymersAcrylic based crusting agents have a similar action to PVA based crusting agents but have stronger bonds that do not soften when wet. As a result, they are suitable for long term crusting applications. Due to their ability to adhere to all materials and not release when wet they can use used on almost any material including non-porous material such as sand, stone and building products.
Acrylic based crusting agents give the longest dust suppression performance and can be used in almost all situations. Their primary limitation compared to the Gelling polymers and New Generation polymers is their cost.
There is significant variability in the acrylic based crusting agents on the market. Acrylic polymers can be long or short chain and single chain or cross linked and these factors impact their performance (long chain and cross-linked give better performance). Some products have virgin acrylic polymer made for this purpose and some suppliers use waste material from other process as their source of acrylic polymer (waste sources typically have 40% of the active polymer) which can give variable performance.
We recommend RST TGC (Total Ground Control) as a quality, virgin material, made for purpose acrylic polymer style crusting agent.
Gelling polymers have become popular in the Australian market due to their low application cost which is typically about 30% to 40% for the same coverage area compared to the acrylic / latex polymers. The gelling polymer crusting agents have a different action to acrylic polymers and while they do not quite have the same crusting life (up to 12 months) as the acrylics (up to 18 months) their flexibility when wet means they are more tolerant to weather. Due to the bonding method of the gelling polymer crusting agents they are only suitable for porous materials, so they are generally not used on stone or building products. The gelling polymers are difficult to dilute due to their gelling behaviour and this can limit their use. They also do not hold the green marking dye as long as the acrylic polymers which is important for some clients.
We recommend RST RT5 Superskin as a quality gelling polymer style crusting agent.
New generation polymers
Ongoing research and development has resulted in the release of our DustWorx GX crusting / veneering agent. DustWorx GX has the ease of dilution, lifespan and suitability for all materials of the acrylic polymers, but with the cost per square meter of the gelling polymer. The holding ability of the green marking dye with the DustWorx GX sits midway between the acrylic polymer and gelling polymer crusting agents.
If you have a particular dust control application you would like to discuss or would like more information on crusting agents and which is the most suitable for your application then please call us on +61 2 6062 3300 or send an email to email@example.com.