Frequently Asked Questions

AS3799 is an Australian Standard titled "Specification and Supply of Concrete Curing Compounds." This standard provides guidelines and requirements for the certification of curing compounds used in concrete construction.

Key Points of AS3799:

Purpose: The standard sets out specifications for curing compounds that help retain moisture in freshly placed concrete, which is essential for the proper hydration of cement, leading to improved strength and durability.

Types of Curing Compounds: AS3799 covers various types of curing compounds, including water-based, solvent-based, and membrane-forming compounds. 

Each type has specific requirements regarding their composition, application, and performance.

Performance Criteria: The standard specifies performance criteria that curing compounds must meet. 

This includes the ability to reduce water loss from the concrete surface and ensure proper curing.

Certification: To comply with AS3799, curing compounds must retain a min. of 90% of the original concrete moisture and be tested and certified to meet the standard's requirements. 

This certification ensures that the products used in construction are effective and reliable for the intended purpose.

Application: The standard provides guidelines on the correct application of curing compounds, including the timing, method of application, and coverage rate of 5m2/L, to ensure optimal performance.

Environmental Considerations: AS3799 also considers the environmental impact of curing compounds, particularly the use of volatile organic compounds (VOCs) in solvent-based products.

Importance:

Certification under AS3799 is important for ensuring that the curing compounds used in concrete construction meet the necessary standards for performance, safety, and environmental impact. This helps in achieving the desired quality and longevity of concrete structures.

Selecting the correct concrete curing compound for your project is crucial to ensure the concrete achieves its desired strength, durability, and surface finish. 

Here are the key factors to consider when choosing a curing compound:

1. Type of Project

Large Structural Elements: For bridges, dams, or large slabs, where extended curing is critical, consider high-efficiency curing compounds like membrane-forming types.

Small or Residential Projects: For smaller projects like driveways, footpaths, or residential slabs, a standard water-based PVA (non-Australian Standard) or hydrocarbon resin to meet Australian Standards AS3799 curing compound may suffice.

2. Curing Compound Type

Water-Based Compounds: These are environmentally friendly, low in volatile organic compounds (VOCs), and easy to apply. Suitable for most general applications.

Solvent-Based Compounds: These offer excellent curing performance but have higher VOC content. Suitable for industrial applications like bitumen or eco friendly concrete.

Membrane-Forming Compounds: Create a physical barrier on the surface, reducing water loss. Ideal for large exposed surfaces like roads and runways.

Wax-Based Compounds: Effective in preventing water loss but may need removal before applying subsequent coatings or finishes and are typically used as a debonding agent.

3. Environmental Conditions

Temperature and Humidity: In hot, dry, or windy conditions, choose a curing compound with high moisture retention (min. 90% to meet AS3799) to prevent rapid water loss from the concrete.

Exposure to Sunlight: For projects with high exposure to sunlight, use curing compounds with UV resistance.

Freezing Conditions: In cold climates, select a curing compound that provides protection against freezing and thawing cycles.

4. Surface Finish Requirements

Textured or Decorative Finishes: Ensure the curing compound does not interfere with the final appearance. Some curing compounds can leave a residue that affects the aesthetic of colored or stamped concrete.

Subsequent Treatments: If the concrete will receive further treatments like sealers, coatings, or flooring, choose a curing compound that is compatible or easily removable.

5. Compliance with Standards

Certification: Ensure the curing compound meets relevant standards, such as AS3799 in Australia, to guarantee its performance.

VOC Content: If environmental regulations or indoor air quality are concerns, choose low-VOC or VOC-free curing compounds.

6. Application Method

Ease of Application: Consider the method of application—spraying, brushing, or rolling—and choose a compound that is easy to apply with the equipment available.

Coverage Rate: Ensure the curing compound can be applied at the recommended coverage rate of 5m2/L for the project to achieve the desired curing effect.

7. Cost and Availability

Budget: Balance performance with cost, ensuring that the chosen curing compound provides the necessary benefits within the project’s budget.

Availability: Ensure the selected curing compound is readily available in the required quantity and timeframe.

8. Manufacturer’s Recommendations

Technical Support: Consult with the manufacturer for recommendations based on your specific project conditions and needs.

Product Data Sheets: Review the technical data sheets provided by manufacturers for detailed information on performance, application instructions, and compatibility.

Conclusion

Choosing the right curing compound involves assessing the project’s specific needs, environmental conditions, and compliance with relevant standards. 

Proper selection ensures the concrete cures effectively, leading to a durable and high-quality final product.

Removing a hydrocarbon resin curing compound from concrete surfaces is important, especially if you plan to apply a subsequent coating, sealer, or finish. 

Here’s a step-by-step guide on how to remove it effectively:

1. Identify the Curing Compound Type

Hydrocarbon Resin-Based: This type of curing compound forms a film on the concrete surface that can be difficult to remove. It’s important to confirm that the compound is indeed hydrocarbon resin-based before proceeding.

Some hydrocarbon resin curing compounds are formulated to oxidise with exposure to UV sunlight, generally speaking this can take anywhere from 6-8 weeks pending the exposure to UV and original application rate has been followed. Refer to manufacturers technical data sheets.

2. Mechanical Removal

Grinding: Use a concrete grinder with a suitable abrasive pad to mechanically grind off the curing compound. This method is effective for large areas or where complete removal is necessary.

3. Chemical Removal

Solvent-Based or Water-Based removers: Apply a chemical remover designed to break down the hydrocarbon resin curing compounds. 

Follow the manufacturer’s instructions carefully regarding application and dwell time.

Application: Use a brush, roller, or sprayer to apply the remover evenly over the surface.

Dwell Time: Allow the remover to sit for the recommended time, depending on the product and the thickness of the curing compound.

Agitation: After the remover has softened the curing compound, use a scrubbing machine or a stiff-bristle brush to remove the residue.

Alkaline Cleaners: In some cases, a strong alkaline cleaner can be effective. These cleaners break down the hydrocarbon resin and can be used in combination with a scrubbing machine.

Dilution: Follow the manufacturer’s instructions to dilute the cleaner appropriately.

Application: Apply the cleaner and agitate the surface with a stiff brush or a floor machine with a scrubbing pad.

Rinse: Thoroughly rinse the surface with water to remove any remaining cleaner and dissolved curing compound.

4. Pressure Washing

After applying a chemical remover or alkaline cleaner, use a pressure washer to remove the remaining residue and cleaning solution.

Pressure Setting: Use a pressure washer set to around 3,000 PSI. Higher pressures can damage the concrete, so adjust accordingly.

Nozzle Type: Use a fan tip nozzle to avoid gouging the concrete surface.

5. Rinsing and Neutralizing

Thorough Rinse: After mechanical or chemical removal, rinse the concrete thoroughly with clean water to remove all residues.

Neutralization: If you used a chemical remover or alkaline cleaner, neutralize the surface with a mild acid solution (like diluted vinegar or a commercial neutralizer) if required by the product’s instructions.

6. Drying

Allow the concrete surface to dry completely before applying any further coatings, sealers, or finishes.

7. Surface Inspection

Inspect the surface to ensure that all traces of the curing compound have been removed. Look for any glossy areas or residue that may indicate remaining compound.

8. Final Preparation

Depending on the next step (e.g., applying a sealer or coating), you may need to lightly sand or etch the surface to ensure good adhesion.

Safety Precautions

Protective Gear: Wear appropriate personal protective equipment (PPE) such as gloves, safety glasses, and respirators when handling chemical strippers or operating mechanical equipment.

Ventilation: Ensure good ventilation when using chemical strippers, especially indoors, to avoid inhaling fumes.

By following these steps, you can effectively remove hydrocarbon resin curing compounds and prepare the concrete surface for the next phase of your project.

Yes, you can use a surface hardener in freshly poured concrete, but it's important to follow proper procedures to ensure the best results. Surface hardeners, also known as dry-shake hardeners, are typically applied to freshly placed concrete to enhance surface durability, abrasion resistance, and in some cases, improve the aesthetic finish.

Steps to Apply a Surface Hardener to Freshly Poured Concrete:

Timing:

Initial Setting: Wait until the concrete has set to the point where the bleed water (excess water rising to the surface) has evaporated, but the concrete is still plastic and workable. The surface should be firm enough to support light foot traffic without significant indentation.

Test the Surface: Lightly press your fingers into the surface. If it leaves only a slight impression without bringing up moisture, it's the right time to apply the hardener.

Application Process:

First Application:

Distribute the Hardener: Broadcast the surface hardener evenly over the concrete surface. The typical method involves applying two-thirds of the total hardener amount in the first pass.

Let it Absorb Moisture: Allow the hardener to absorb the moisture from the concrete. The hardener will darken as it draws in moisture.

Troweling: Once the hardener has absorbed sufficient moisture, use a trowel (either by hand or power trowel) to work it into the surface. This helps integrate the hardener with the concrete matrix.

Second Application:

Apply the Remaining Hardener: Evenly distribute the remaining one-third of the hardener on the surface.

Troweling Again: After the second application has absorbed moisture, trowel the surface again. This step ensures uniform distribution and enhances surface finish and durability.

Finishing:

Final Troweling: Conduct final troweling passes to achieve the desired surface finish, whether it's a smooth, textured, or decorative finish.

Control Joints: If control joints are required, cut them as needed to prevent random cracking.

Curing:

Proper Curing: After finishing, it's crucial to properly cure the concrete to ensure the hardener bonds well and the concrete achieves its full strength. This can be done using curing compounds (as per AS3799) or by maintaining moisture using wet coverings.

Considerations:

Consistency: Ensure the surface hardener is evenly distributed to avoid areas of varying hardness or color. Inconsistent application can lead to a patchy finish.

Compatibility: Verify that the chosen surface hardener is compatible with the concrete mix and any other treatments (e.g., sealers) that will be applied later.

Environmental Conditions: Wind, temperature, and humidity can affect the application. Hot and windy conditions can accelerate drying, making it challenging to apply the hardener properly. Consider adjustments or additional curing methods in extreme weather.

Benefits of Using a Surface Hardener:

Increased Durability: Provides a tougher, more wear-resistant surface, ideal for high-traffic areas.

Enhanced Aesthetics: Some surface hardeners can add color or a polished finish to the concrete.

Improved Surface Strength: Enhances resistance to abrasion, impact, and, in some cases, chemical exposure.

Conclusion:

Using a surface hardener on freshly poured concrete is an effective way to enhance its surface properties, but careful attention to timing, application, and curing is essential for success.

The recommended application rate for concrete curing compounds to meet the Australian Standard AS3799 depends on the specific product being used and its type. However, AS3799 provides general guidelines to ensure that the curing compound is applied adequately to achieve effective curing. Below are some typical recommendations:

1. General Application Rate:

Water-Based Curing Compounds:

Coverage Rate: Typically, water-based curing compounds should be applied at a rate of 5 square meters per liter (m²/L).

Membrane-Forming Curing Compounds:

Coverage Rate: For membrane-forming compounds, the rate is often 5 square meters per liter (m²/L).

2. Manufacturer’s Recommendations:

Always check the specific product’s technical data sheet provided by the manufacturer. The application rate might vary depending on the product’s formulation, intended use, and specific performance requirements.

The manufacturer’s guidelines should align with AS3799 but may include additional instructions for optimal performance based on the product's characteristics.

3. Factors Influencing Application Rate:

Surface Texture: Rough or porous surfaces may require a higher application rate to ensure full coverage and effective moisture retention.

Environmental Conditions: Hot, dry, or windy conditions may necessitate a slightly higher application rate or even reapplication to counteract accelerated evaporation.

Concrete Type: High-performance or dense concrete mixes might require different curing strategies or rates to ensure effective curing.

4. Compliance with AS3799:

AS3799 specifies that the curing compound should form a continuous, unbroken film on the concrete surface to effectively reduce water loss.

The standard requires that the curing compound be applied uniformly and at a rate that ensures complete coverage, without leaving gaps or thin spots that could compromise the curing process.

5. Application Method:

Spraying: The most common method of applying curing compounds is by spraying. Ensure that the spray equipment is calibrated to deliver the compound at the recommended rate.

Rolling or Brushing: These methods can be used for smaller areas or when a spray application is not feasible, but care must be taken to achieve uniform coverage.

6. Verification:

Field Test: To verify compliance with AS3799, conduct a field test by applying the compound at the recommended rate over a measured area and checking the coverage.

Conclusion:

To meet the requirements of AS3799, ensure that you apply the curing compound at the manufacturer’s recommended rate, typically 5 square meters per liter, depending on the type of compound. Always follow the specific instructions provided by the manufacturer and adjust for environmental conditions and surface texture to ensure adequate curing.

Aliphatic alcohol, commonly referred to as an evaporation retarder, is a liquid compound used during the finishing process of concrete to control the rate of surface moisture evaporation. It is particularly useful in conditions where rapid evaporation can lead to problems such as plastic shrinkage cracking. Here's how and why it is used:

Purpose of Aliphatic Alcohol/Evaporation Retarder:

Reduce Evaporation Rate:

Aliphatic alcohol forms a thin, temporary film on the surface of freshly placed concrete. This film slows down the rate of water evaporation from the concrete surface, which is crucial in hot, windy, or dry conditions where evaporation can occur too quickly.

Minimize Plastic Shrinkage Cracking:

Rapid moisture loss from the surface of fresh concrete can cause plastic shrinkage cracking. By using an evaporation retarder, you help maintain surface moisture and reduce the risk of these cracks forming before the concrete has had a chance to properly set.

Aid in Finishing:

It can make finishing operations easier by maintaining a workable surface longer, allowing for better timing and quality of finishing processes like floating, troweling, and texturing.

When to Use Aliphatic Alcohol:

Hot Weather: In hot conditions, evaporation rates are higher, increasing the risk of rapid drying. Aliphatic alcohol helps retain moisture on the surface.

Windy Conditions: Wind accelerates the evaporation of water from the concrete surface, which can lead to drying out before proper finishing can occur. The use of an evaporation retarder is beneficial in such conditions.

Low Humidity: In low humidity environments, water evaporates faster from the surface of the concrete, which can cause similar issues as hot and windy conditions.

Large Surface Areas: When working with large concrete pours, the finishing process can take longer, increasing the risk of uneven drying. Applying an evaporation retarder can help maintain a uniform moisture level across the entire surface.

How to Apply Aliphatic Alcohol:

Mixing:

Aliphatic alcohols usually come as concentrated liquids that need to be diluted with water before application. Follow the manufacturer’s instructions for the correct dilution ratio.

Timing:

Apply the aliphatic alcohol immediately after screeding and before finishing operations begin. This is usually when the concrete has just begun to lose its sheen, and the surface is starting to dry.

Application Method:

Spraying: The most common method of application is by spraying. Use a fine mist sprayer to apply the evaporation retarder evenly across the surface of the concrete. Avoid over-application, which can cause the film to become too thick, leading to problems with finishing.

Reapplication:

Depending on environmental conditions and the time required for finishing, you may need to reapply the aliphatic alcohol. This can be done as needed to maintain the moisture level, but be sure to follow the manufacturer's guidelines to avoid issues.

Limitations and Considerations:

Temporary Effect: Aliphatic alcohol is only a temporary measure to slow evaporation. It is not a substitute for proper curing methods like water curing or curing compounds, which are necessary to ensure long-term hydration and strength development.

Compatibility: Ensure that the evaporation retarder is compatible with other concrete admixtures or surface treatments that may be used in the project.

Environmental Conditions: While aliphatic alcohol can help manage evaporation, it’s still essential to consider other protective measures like wind breaks or shading in extreme conditions.

Conclusion:

Aliphatic alcohol, or evaporation retarder, is an effective tool for managing surface moisture loss during the concrete finishing process, particularly in challenging environmental conditions. By controlling evaporation rates, it helps prevent plastic shrinkage cracking and allows for better finishing, ultimately contributing to a higher-quality concrete surface.